Highway Capacity Manual 2000
TWSC - UNSIGNALIZED INTERSECTIONS WORKSHEET
Worksheet 1
General Information
Analyst
Agency or Company
Date Performed
Analysis Time Period
Site Information
______________________
______________________
______________________
______________________
Intersection
Jurisdiction
Analysis Year
________________________
________________________
________________________
Geometrics and Movements
grade = ______
Street
v12 v11 v10
Show North
STOP
grade = ______
v6
v5
v4
v16
v13
S2
v1
v2
v3
S5
v14
v15
grade = ______
STOP
Street
v7 v 8 v9
grade = ______
Length of study period = _____ h
Worksheet 2
Vehicle Volumes and Adjustments
Vehicle Volumes and Adjustments
Movement
1
2
3
4
5
6
7
8
9
10
11
Volume (veh/h)
Peak-hour factor, PHF
Hourly flow rate (veh/h)
Proportion of heavy vehicles, PHV
Pedestrian Volumes and Adjustments
Movement
Flow, Vx (ped/h)
Lane width, w (ft)
Walking speed,1 Sp (ft/s)
Percent blockage, fp (Equation 17-11)
1. Default walking speed = 4.0 ft/s
Chapter 17 - Unsignalized Intersections
13
14
15
16
12
Highway Capacity Manual 2000
TWSC - UNSIGNALIZED INTERSECTIONS WORKSHEET
Worksheet 3
General Information
Project Description _________________________________________________________________________________
Lane Designation
Movements
Lane 1
Lane 2
Lane 3
Grade, G
Right Turn
Channelized?
1, 2, 3
4, 5, 6
7, 8, 9
10, 11, 12
Flared Minor-Street Approach
Movement 9
q Yes
q No
Storage space, n
________________
(number of vehicles)
Movement 12
q Yes
q No
Storage space, n
________________
(number of vehicles)
Median Storage*
* Includes raised or striped median (RM), or two-way left-turn lane (TWLTL)
Type
Movements 7 and 8
q Yes
_____
q No
Storage space, m
________________
(number of vehicles)
Movements 10 and 11
q Yes
_____
q No
Storage space, m
________________
(number of vehicles)
Upstream Signals
Movements
S2
Distance to
Signal, D (ft)
Prog Speed,
Sprog (mi/h)
Cycle
Length, C (s)
Green Time,
geff (s)
protected LT
Arrival
Type
Saturation Flow Progressed Flow,
Rate, s (veh/h)
Vprog (veh/h)
3
TH
S5
protected LT
3
TH
Computing Delay to Major-Street Vehicles
Data for Computing Effect of Delay to Major-Street Vehicles
Shared-lane volume, major-street through vehicles, vi1, blocked by LT
Shared-lane volume, major-street right-turn vehicles, vi2, blocked by LT
Saturation flow rate, major-street through vehicles, si1
Saturation flow rate, major-street right-turn vehicles, si2
Number of major-street through lanes
Length of study period, T (h)
S2 Approach
S5 Approach
Chapter 17 - Unsignalized Intersections
Highway Capacity Manual 2000
TWSC - UNSIGNALIZED INTERSECTIONS WORKSHEET
Worksheet 4
General Information
Project Description _________________________________________________________________________________
Critical Gap and Follow-Up Time
tc = tc,base + tc,HV PHV + tc,G G - tc,T - t3,LT
Major LT
Movement
Minor RT
Minor TH
Minor LT
1
4
9
12
8
11
7
10
-
-
0.1
0.1
0.2
0.2
0.2
0.2
tc,base (Exhibit 17-5)
tc,HV
PHV (from Worksheet 2)
tc,G
G (from Worksheet 3)
t3,LT
tc,T
single stage
two stage
tc (Equation 17-1)
single stage
two stage
tf = tf,base + tf,HV PHV
Major LT
Movement
tf,base (Exhibit 17-5)
tf,HV
1
Minor RT
4
9
Minor TH
12
8
Minor LT
11
7
10
PHV (from Worksheet 2)
tf (Equation 17-2)
Worksheet 5a
Time to Clear Standing Queue (Computation 1)
Movement 2
VT,prog
Movement 5
VL,prot
VT,prog
VL,prot
Effective green, geff (s)
Cycle length, C (s)
Saturation flow rate, s (veh/h)
Arrival type
vprog (veh/h)
Rp (from Chapter 16)
Proportion of vehicles arriving
on green, P (Equation 17-17)
gq1 (Equation 17-18)
gq2 (Equation 17-19)
gq (Equation 17-20)
Chapter 17 - Unsignalized Intersections
3
3
1.00
1.00
Highway Capacity Manual 2000
TWSC - UNSIGNALIZED INTERSECTIONS WORKSHEET
Worksheet 6
General Information
Project Description _________________________________________________________________________________
Impedance and Capacity Calculation
Step 1: RT from Minor Street
v9
v12
Conflicting flows (Exhibit 17-4)
vc,9 =
vc,12 =
Potential capacity (Equation 17-3 or 17-29)
cp,9 =
cp,12 =
Ped impedance factor (Equation 17-12)
pp,9 =
pp,12 =
Movement capacity (Equation 17-4)
cm,9 = cp,9 pp,9 =
cm,12 = cp,12 pp,12 =
Prob of queue-free state (Equation 17-5)
p0,9 =
p0,12 =
Step 2: LT from Major Street
v4
v1
Conflicting flows (Exhibit 17-4)
vc,4 =
vc,1 =
Potential capacity (Equation 17-3 or 17-29)
cp,4 =
cp,1 =
Ped impedance factor (Equation 17-12)
pp,4 =
pp,1 =
Movement capacity (Equation (17-4)
cm,4 = cp,4 pp,4 =
cm,1 = cp,1 pp,1 =
Prob of queue-free state (Equation 17-5)
p0,4 =
p0,1 =
Major left shared lane prob of queue-free state (Equation 17-16)
* =
p0,4
* =
p0,1
Step 3: TH from Minor Street (4-leg intersections only)
v8
v11
Conflicting flows (Exhibit 17-4)
vc,8 =
vc,11 =
Potential capacity (Equation 17-3 or 17-29)
cp,8 =
cp,11 =
Ped impedance factor (Equation 17-12)
pp,8 =
pp,11 =
Capacity adjustment factor due to impeding movement
(shared lane use p*) (Equation 17-13)
f8 = p0,4 p0,1 pp,8 =
f11 = p0,4 p0,1 pp,11 =
Movement capacity (Equation 17-7)
cm,8 = cp,8 f8 =
cm,11 = cp,11 f11 =
Prob of queue-free state
p0,8 =
Step 4: LT from Minor Street (4-leg intersections only)
Conflicting flows (Exhibit 17-4)
p0,11 =
v10
v7
vc,7 =
vc,10 =
Potential capacity (Equation 17-3 or 17-29)
cp,7 =
cp,10 =
Ped impedance factor (Equation 17-12)
pp,7 =
pp,10 =
Major left, minor through impedance factor
p''7 = p0,11 f11 =
'' = p f =
p10
0,8 8
Major left, minor through adjusted impedance factor
(Equation 17-8)
p'7
' =
p10
Capacity adjustment factor due to impeding movements
(Equation 17-14)
f7 = p7' p0,12 pp,7 =
' p p
f10 = p10
0,9 p,10 =
Movement capacity (Equation 17-10)
cm,7 = f7 cp,7 =
cm,10 = f10 cp,10 =
=
Step 5: LT from Minor Street (T-intersections only)
v7
v10
Conflicting flows (Exhibit 17-4)
vc,7 =
vc,10 =
Potential capacity (Equation 17-3 or 17-29)
cp,7 =
cp,10 =
Ped impedance factor (Equation 17-12)
pp,7 =
pp,10 =
Capacity adjustment factor due to impeding movement
(shared lane use p*) (Equation 17-13)
f7 = p0,4 p0,1 pp,7 =
f10 = p0,4 p0,1 pp,10 =
Movement capacity (Equation 17-7)
cm,7 = cp,7 f7 =
cm,10 = cp,10 f10 =
Notes
1. For 4-leg intersections use Steps 1, 2, 3, and 4.
2. For T-intersections use Steps 1, 2, and 5.
Chapter 17 - Unsignalized Intersections
Highway Capacity Manual 2000
TWSC - UNSIGNALIZED INTERSECTIONS WORKSHEET
Worksheet 8
General Information
Project Description _________________________________________________________________________________
Shared-Lane Capacity
cSH =
∑vy
y
∑ vy
y cm,y
(Equation 17-15)
( )
v (veh/h)
Lane
cm (veh/h)
Movement 7
Movement 8
Movement 9
Movement 7
Movement 8
Movement 9
Movement 10
Movement 11
Movement 12
Movement 10
Movement 11
Movement 12
cSH (veh/h)
1
2
3
1
2
3
Worksheet 9
Effect of Flared Minor-Street Approaches
Lane _________
Movement 7
csep (from Worksheet 6 or 7)
volume (from Worksheet 2)
delay (Equation 17-38)
Qsep (Equation 17-34)
Qsep + 1
round (Qsep + 1)
nmax (Equation 17-35)
cSH
csep
n
cact (Equation 17-36)
Chapter 17 - Unsignalized Intersections
Movement 8
Lane _________
Movement 9
Movement 10
Movement 11
Movement 12
Highway Capacity Manual 2000
TWSC - UNSIGNALIZED INTERSECTIONS WORKSHEET
Worksheet 10
General Information
Project Description _________________________________________________________________________________
Control Delay, Queue Length, Level of Service
Lane
v (veh/h)
1 7
8
9
2 7
8
9
3 7
8
9
cm (veh/h)
v/c
Queue Length Control Delay
LOS
(Equation 17-37) (Equation 17-38) (Exhibit 17-2)
Delay and LOS
1 10 11 12
2 10 11 12
3 10 11 12
Movement
v (veh/h)
cm (veh/h)
v/c
Queue Length
(Equation 17-37)
Control Delay
(Equation 17-38)
LOS
(Exhibit 17-2)
1
4
Worksheet 11
Delay to Rank 1 Vehicles
S2 Approach
p0,j (Equation 17-5)
S5 Approach
p0,1 =
p0,4 =
p*0, 1 =
p*0, 4 =
vi1, volume for Stream 2 or 5
vi2, volume for Stream 3 or 6
si1, saturation flow rate for Stream 2 or 5
si2, saturation flow rate for Stream 3 or 6
* (Equation 17-16)
p0,j
dmajor left, delay for Stream 1 or 4
N, number of major-street through lanes
dRank 1, delay for Stream 2 or 5 (Equation 17-39)
Chapter 17 - Unsignalized Intersections
2/18/2020
Un‐signalized Intersections
• TWSC
• AWSC
• Roundabouts
1
TWSC
2
1
2/18/2020
LOS
3
Traffic Streams
Rank
1.
2.
3.
4.
Sub‐script
i.
j.
k.
l.
4
2
2/18/2020
Traffic Streams
5
Conflicting Flows
• See handout
6
3
2/18/2020
Critical Gap
• tc
– The minimum time interval in the major‐street
traffic stream that allows intersection entry for a
minor‐street vehicle
7
Critical Gap
8
4
2/18/2020
Critical Gap
• tc,T
– Only for movements 7, 8, 10 and 11
• Base factors for six‐lane major street are
assumed to be same for four lane street
9
Follow Up Time
• tf
– The time between the departure of one vehicle
from the minor street and the departure of the
next vehicle
• Same major‐street gap
• Continuous queueing
10
5
2/18/2020
Follow Up Time
11
Potential Capacity
12
6
2/18/2020
Potential Capacity
• Assumptions
– Traffic from nearby intersections does not back up
into subject intersection
– A separate lane is provided on the minor street for
exclusive use of each movement
– An upstream signal does not affect the arrival
pattern of the major‐street traffic
– No other Rank 2, 3 or 4 movements to impeded
the subject movement
13
14
7
2/18/2020
15
Impedance Effects
• See Handout
16
8
2/18/2020
Pedestrian Impedance
17
Pedestrian Impedance
18
9
2/18/2020
Shared Lane Capacity
• Minor‐Street Approaches
19
Shared Lane Capacity
• Major‐Street Approaches
20
10
2/18/2020
Upstream Signals
• Flow Regimes
1.
2.
3.
4.
No Platoons
Platoon from left only
Platoon from right only
Platoons from both directions
21
Upstream Signals
22
11
2/18/2020
Two‐Stage Gap Acceptance
23
Flared Minor‐Street Approaches
24
12
2/18/2020
Estimating Queue Lengths
25
Only when T = 0.25 (15‐min period)
26
13
2/18/2020
Control Delay
27
Control Delay for 15‐min period
28
14
2/18/2020
Delay to Rank 1 vehicles
• Occurs in shared lanes of major‐street
approaches when left turning vehicles block
through (and right turning) vehicles.
29
Approach Delay
30
15
2/18/2020
Intersection Delay
31
AWSC
32
16
2/18/2020
AWSC
• Two, One‐Way Streets
33
AWSC
• Two, Two‐Way Streets
34
17
2/18/2020
AWSC
• Based on the probability of the degree of
conflict for the number of lanes per approach
35
Roundabouts
36
18
2/18/2020
Roundabouts
37
Roundabouts
38
19
2/18/2020
Roundabouts
39
Homework
• Use worksheets
40
20
2/18/2020
Homework
• You will also need the following
– Use PHF = 1.00
41
21
Highway Capacity Manual 2000
EXHIBIT 17-4. DEFINITION AND C OMPUTATION OF CONFLICTING F LOWS
The following footnotes
apply to Exhibit 17-4:
[a] If right-turning traffic
from the major street is
separated by a triangular
island and has to comply
with a yield or stop sign,
v6 and v3 need not be
considered.
[b] If there is more than
one lane on the major
street, the flow rates in
the right lane are
assumed to be v 2/N or
v5/N, where N is the
number of through lanes.
The user can specify a
different lane distribution
if field data are available.
Subject and Conflicting Movements
Conflicting Traffic Flows, vc,x
Subject
Movement
16
4
2
6
Major LT
(1, 4)
3
5
15
1
vc,1 = v5 + v6[a] + v16
vc,4 = v2 + v3[a] + v15
12
14
2
Minor RT
(9, 12)
[c] If there is a right-turn
lane on the major street,
v3 or v6 should not be
considered.
[d] Omit the farthest
right-turn v3 for Subject
Movement 10 or v6 for
Subject Movement 7 if
the major street is
multilane.
[e] If right-turning traffic
from the minor street is
separated by a triangular
island and has to comply
with a yield or stop sign,
v9 and v12 need not be
considered.
[f] Omit v9 and v12 for
multilane sites, or use
one-half their values if
the minor approach is
flared.
16
6
15
3
13
5
9
v2[b]
vc,9 =
N
+ 0.5v3[c] + v14 + v15
vc,12 =
v5[b]
+ 0.5v6[c] + v13 + v16
N
Stage I
11
1
2
3
15
6
5
4
16
8
Minor TH
(8, 11)
vc,I,8 = 2v1 + v2 + 0.5v3[c] + v15
Stage II
vc,I,11 = 2v4 + v5 + 0.5v6[c] + v16
16
6
5
4
1
2
3
vc,II,8 = 2v4 + v5 + v6[a] + v16
15
vc,II,11 = 2v1 + v2 + v3[a] + v15
Stage I
10
1
2
3
15
6
5
4
16
7
Minor LT
(7, 10)
vc,I,7 = 2v1 + v2 + 0.5v3[c] + v15
Stage II
vc,I,10 = 2v4 + v5 + 0.5v6[c] + v16
12 11
1
2
3
6
5
4
13
14
8
9
v5
v
vc,II,7 = 2v4 +
+ 0.5v6[d] + 0.5v12[e,f] + 0.5v11 vc,II,10 = 2v1 + 2 + 0.5v3[d] + 0.5v9[e,f] +
N
N
+ v13
0.5v8 + v14
Chapter 17 - Unsignalized Intersections
Methodology - TWSC Intersections
17-6
Highway Capacity Manual 2000
EXHIBIT 17-7. POTENTIAL CAPACITY FOR FOUR-LANE STREETS
2000
LT Major
RT Minor
TH Minor
LT Minor
Potential Capacity, cp,i (veh/h)
1500
1000
500
0
0
500
1000
1500
2000
2500
3000
Conflicting Flow Rate, vc,x (veh/h)
Impedance Effects
Vehicle Impedance
Vehicles use gaps at a TWSC intersection in a prioritized manner. When traffic
becomes congested in a high-priority movement, it can impede lower-priority movements
(i.e., streams of Ranks 3 and 4) from using gaps in the traffic stream, reducing the
potential capacity of these movements.
Major traffic streams of Rank 1 are assumed to be unimpeded by any of the minor
traffic stream movements. This rank also implies that major traffic streams are not
expected to incur delay or slowing as they travel through the TWSC intersection.
Empirical observations have shown that such delays do occasionally occur, and they are
accounted for by using adjustments provided in the procedures.
Minor traffic streams of Rank 2 (including left turns from the major street and right
turns from the minor street) must yield only to the major-street through and right-turning
traffic streams of Rank 1. There are no additional impedances from other minor traffic
streams, and so the movement capacity of each Rank 2 traffic stream is equal to its
potential capacity as indicated by Equation 17-4.
c m,j = cp,j
(17-4)
Compute c p,j using
Equation 17-3
where j denotes movements of Rank 2 priority.
Minor traffic streams of Rank 3 must yield not only to the major traffic streams, but
also to the conflicting major-street left-turn movement, which is of Rank 2. Thus, not all
gaps of acceptable length that pass through the intersection will normally be available for
use by Rank 3 traffic streams, because some of these gaps are likely to be used by the
major-street left-turning traffic. The magnitude of this impedance depends on the
probability that major-street left-turning vehicles will be waiting for an acceptable gap at
the same time as vehicles of Rank 3. A higher probability that this situation will occur
means greater capacity-reducing effects of the major-street left-turning traffic on all Rank
3 movements.
17-9
Chapter 17 - Unsignalized Intersections
Methodology - TWSC Intersections
Highway Capacity Manual 2000
What is of interest to the analyst, therefore, is the probability that the major-street
left-turning traffic will operate in a queue-free state. This probability is expressed by
Equation 17-5:
If major-street through
and left-turn movements
are shared, use Equation
17-16. Also use
Equation 17-5 to
compute the probability
of queue-free state for
Rank 3 movements.
p0, j = 1 −
vj
c m, j
(17-5)
where j = 1, 4 (major-street left-turn movements of Rank 2).
The movement capacity, c m,k, for all Rank 3 movements is found by calculating a
capacity adjustment factor that accounts for the impeding effects of higher-ranked
movements. The capacity adjustment factor is denoted by fk for all movements k and for
all Rank 3 movements and is given by Equation 17-6.
f k = ∏ p0, j
(17-6)
j
where
p0,j
k
= probability that conflicting Rank 2 movement j will operate in a
queue-free state, and
= Rank 3 movements.
The movement capacity for the Rank 3 movements is computed using Equation 17-7.
c m,k = (cp,k)fk
Also account for
pedestrian impedance, if
significant
(17-7)
Rank 4 movements (i.e., only the minor-street left turns at a four-leg intersection)
can be impeded by the queues of three higher-ranked traffic streams:
• Major-street left-turning movements (Rank 2),
• Minor-street crossing movements (Rank 3), and
• Minor-street right-turning movements (Rank 2).
If the intersection has three legs, then the minor-street left turn is a Rank 3 movement and
should be evaluated using Equations 17-5 through 17-7.
The probability that each of these higher-ranked traffic streams will operate in a
queue-free state is central to determining their overall impeding effects on the
minor-street left-turn movement. At the same time, it must be recognized that not all of
these probabilities are independent of each other. Specifically, queuing in the
major-street left-turning movement affects the probability of a queue-free state in the
minor-street crossing movement. Applying the simple product of these two probabilities
will likely overestimate the impeding effects on the minor-street left-turning traffic.
Exhibit 17-8 can be used to adjust for the overestimate caused by the statistical
dependence between queues in streams of Ranks 2 and 3. The mathematical
representation of this curve is given by Equation 17-8.
p ′ = 0.65 p ′′ −
p ′′
+ 0.6 p ′′
p ′′ + 3
(17-8)
where
p'
p"
p0,j
p0,k
Chapter 17 - Unsignalized Intersections
Methodology - TWSC Intersections
= adjustment to the major-street left, minor-street through impedance
factor;
= (p0,j)(p0,k);
= probability of a queue-free state for the conflicting major-street
left-turning traffic; and
= probability of a queue-free state for the conflicting minor-street
crossing traffic.
17-10
Highway Capacity Manual 2000
EXHIBIT 17-8. ADJUSTMENT TO IMPEDANCE FACTORS FOR
MAJOR LEFT TURN, MINOR T HROUGH
1
0.9
0.8
0.7
p'
0.6
0.5
0.4
0.3
0.2
0.1
0
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
p" = (P0,j)(P0,k)
The capacity adjustment factor for the Rank 4 minor-street left-turn movements can
be computed by Equation 17-9:
f l = (p')(p0 ,j)
(17-9)
where
l
j
= minor-street left-turn movement of Rank 4 (Movements 7 and 10 in
Exhibit 17-3), and
= conflicting Rank 2 minor-street right-turn movement (Movements 9
and 12 in Exhibit 17-3).
The variable p0,j should be included in Equation 17-9 only if movement j is identified as a
conflicting movement. Refer to Exhibit 17-4 and the associated notes.
Finally, the movement capacity for the minor-street left-turn movements of Rank 4
can be determined from Equation 17-10:
c m,l = (fl )(cp,l)
(17-10)
Compute c p,l using Equation
17-3
where l indicates movements of Rank 4 priority.
Rank 4 movements occur only at four-leg intersections. Equations 17-8 to 17-10 are
only required when evaluating four-leg intersections.
Pedestrian Impedance
Minor-street vehicle streams must yield to pedestrian streams. Exhibit 17-9 shows
the relative hierarchy between pedestrian and vehicular streams used in this methodology.
A factor accounting for pedestrian blockage is computed by Equation 17-11 on the basis
of pedestrian volume, the pedestrian walking speed, and the lane width.
f pb =
(v x ) Sw
p
3600
(17-11)
17-11
Chapter 17 - Unsignalized Intersections
Methodology - TWSC Intersections
1/22/20
Colonial Era Transportation
• Coastline and Inland Waterways
– Ferris for hire
• Primitive Roads / English tradition
– Planning, building and maintaining roads rested
with local jurisdictions
– Travel free of charge
– Maintained primarily by statute labor
• All men over 16 required to perform road work on
appointed days
Turnpikes
• Post: War of Independence
• Challenges: Topography and Finance
– War debt, states not in a position to finance
needed, new roads
– Private companies permitted to build
transportation linkages
• English tradition, again
– Chartered by the states
• Regulated Monopolies
Turnpikes
• Role of Federal Government
– Building military roads, only
• New US Constitution
– Strict interpretation
• Recognize sovereignty of the states
– Transportation is a matter of ‘local’ concern
1
1/22/20
Turnpikes
• Albert Gallatin
– Secretary of Treasury
– 1807, First Federal Survey of National
transportation resources
– First to recognize the importance of a good,
national transportation network to the growth
and unity of the nation.
Turnpikes
• One notable exception to Fed ‘hands off
policy’
– First ‘national’ road
• The Cumberland Road
– Presently US 40
– DC to Chicago (MD, VA, PA, OH, IN, IL)
• The Lincoln Highway
– Presently US 30
– Philadelphia to Chicago
» Lancaster Avenue/Lancaster Pike
2
1/22/20
3
1/22/20
Turnpikes
• Original pavement
– Heavy stone structural foundation
• French
– Wooden Planks
• By 1820, using ‘MacAdam’ method
– John MacAdam, Scottish engineer
– Small, tightly packed stones, over native soil
• Tar or oil added later
4
1/22/20
Rural Highways
• By 1880s, urban streets in pretty good shape
• …but rural roads in ‘bad’ shape
• Federal Government began extending aid to
states and municipalities
• First State Highway Plan
– Massachusetts
• 1894, Commonwealth Highway Plan
Rural Highways
• 1896
– US Congress approves designated Mail Routes
• $$ Incentives to states to maintain roads on Mail
Routes
– US Department of Agriculture
• ORI
– Office of Road Inquiry
Rural Highways
• ORI becomes…
• ….OPRI (1899), which becomes…
• Office of Public Road Inquiry
• …OPR, (1905), which becomes…
• Office of Public Roads
• …BPR, which is merged into the…
• Bureau of Public Roads
• FHWA (1966)
– Part of the newly formed US DOT
5
1/22/20
Rural Highways
• ORI
– Good Roads National Map
• 1912
– US Mail experiment/testing
• 1914
– AASHO formed
• Federal Road Act of 1916
– First Federal Aid Highway Bill
– 50/50 split (construction only)
• Like Federal Railway Act of 1916
Rural Highways
• Federal Aid Highway Act of 1921
– Each state required to designate 7% of their total
mileage to a national system eligible for federal
aid
• Great Depression, 1930s
– WPA builds roads
• Hayden-Cartwright Act, 1934
– Can spend up to 1.5% of Fed Highway $$ on
design
Rural Highways
• Federal Aid Highway Act of 1944
– First bill to start the concept of a ‘national’ interstate
system
– Extended federal aid to urban areas
• Federal Aid Highway Act of 1948
– First to look at a national system from a defense
perspective
– Identified many deficiencies
– Gave rise to the modern, publically owned, toll road
movement until…
6
1/22/20
Rural Highways
• Federal Highway Act – 1956
– Companion Highway Revenue Act
– Redefined the role of Fed and State governments
in highway planning
Federal Highway Act – 1956
• Allowed Federal funding of the secondary
system
• Mandated the construction of a national
interstate system
• Established the Highway Trust Fund and the
90/10 funding split
• Formalized the planning process, required
planning studies and public hearings.
7
1/22/20
8
1/22/20
Development of Formal Planning
• Federal Aid Highway Act of 1962
– By 1965, eligibility for federal aid in urban areas
based on the existence of long range plans based
on a:
• Continuing
• Comprehensive
– Transportation planning process carried out
• Cooperatively
– By states and local communities
3C Planning Process
• Federal Highway Act of 1968
– TOPICS
• Traffic Operations Program to Increase Capacity and
Safety
• ADA, 1990
– Transportation and buildings
9
1/22/20
Toward a Systems Approach
• 1975
– Metropolitan Planning Organizations (MPOs)
• Long Range (20 year) Plan
• TSM
• TIP
ISTEA 1991
I. Surface Transportation (Highways)
II. Highway Safety
III. Federal Transit Act Amendments of 1991
IV. Motor Carrier Act of 1991
V. Intermodal Transportation
VI. Research
VII. Air Transportation
VIII.Extended Highway-related taxes & the Highway
Trust Fund
10
1/22/20
ISTEA 1991
1. Mandated by 1995, the NHS
– 155,000 miles of highways
– All interstates
– Most urban and rural principal arterials
2. Funded research and development of IVHS
and renamed it…ITS
ISTEA 1991
3. Mandated statewide planning process
–
–
–
–
–
–
Pavement management
Bridge management
Highway safety
Traffic congestion
Public transportation
Intermodal transportation
11
1/22/20
ISTEA 1991
4. MPOs must integrate long range plans and
TIPs
5. Allowed fed highway funds to be used for
transportation related environmental
projects
Wetlands
Habitat protection
Air quality improvement
Highway beautification
–
–
–
–
ISTEA 1991
6. Strengthened Fed support for Toll facilities
7. Renamed UMTA, FTA
– Added rural and intercity services
8. Extended Trust Fund to FY 1999
– Fed share
•
•
•
Interstates: 90%
Other Roads: 80%
Transit Operating Assistance: 50%
TEA-21
• ISTEA expired 1997, extended to 1998
– 217 Billion appropriation
– Through 2003
– “No states return less than 90.5%”
12
1/22/20
SAFETEA-LU
• Safe, Accountable, Flexible, Efficient
Transportation Equity Act: A Legacy for Users
• TEA-21 expired 2003
• Passed 2005
• 244.1 Billion
– Largest transportation bill in US History
• Moved the 90.5% to 92% by 2008
• Since 2009
– Continuing resolutions
Transportation Funding
Pennsylvania
The issue
• TAC Report: $3.5 billion annual
funding gap
• PA to spend less on highways this
year than in 2007
• Last PA gas tax increase – 1997
• Last federal gas tax increase – 1993
• Gas tax revenue does not increase
with gas price
• Federal energy policy encourages
conservation
• Act 44 was a two-edged sword
13
1/22/20
• 20,000 miles of Pennsylvania highways were
expected to last 40 years when built more than
40 years ago (we now expect longer life). To
prevent more from passing the 40-year mark,
we aim to reconstruct 300 to 500 miles per year.
In the past 20 years we have fallen well short of
this target. The recent focus on bridges has
nearly ended the pavement reconstruction
program.
14
1/22/20
15
1/22/20
Supporting research
•American Road & Transportation Builders Association
• 50,000 additional jobs, mostly non-construction
•The Road Information Program
• Average PA motorist pays up to $1,500/yr. in additional operating
costs
•Texas Transportation Institute
• Some PA commuters waste an entire work week and
$1,000/yr.
•Nat’l Surface Transportation Policy & Revenue Commission
• U.S. should spend $225 billion/yr., not $80 billion
•Pacific Institute for Research & Evaluation
• Roadway condition contributes in 52.7% of 42,000 deaths/yr.
PA’s Aging Transportation System
Capacity Adding Projects
30%
25%
Statewide Percent of Transportation Improvement Programs (TIPs)
adopted by metropolitan and rural planning organizations
25%
23%
20%
20%
13%
15%
10%
5%
5%
13
3.7%
0%
2001-2004
2003-2006
2005 - 08
2007 - 10
2009 - 12
2011 - 14
16
1/22/20
17
2/1/18
Traffic Stream Flow Models
• Vehicle Following concept
• Uninterrupted Flow
– The only interference a single vehicle experiences
is that of other vehicles
Vehicle Following
• v = initial speed of two
vehicles
• dl = deceleration rate of
lead vehicle
• df = deceleration rate of
following vehicle
• PRT = perception-reaction
time
• xo = margin of safety after
stop
• L = length of vehicle
• N =number of vehicles in
‘train’
• Under constant
deceleration, Braking
Distance of the leading
vehicle:
xl = v2/2dl
1
2/1/18
Vehicle Following
• v = initial speed of two
vehicles
• dl = deceleration rate of
lead vehicle
• df = deceleration rate of
following vehicle
• PRT = perception-reaction
time
• xo = margin of safety after
stop
• L = length of vehicle
• N =number of vehicles in
‘train’
• Distance covered by
following vehicle:
xf = vPRT + v2/2df
Vehicle Following
• v = initial speed of two
vehicles
• dl = deceleration rate of
lead vehicle
• df = deceleration rate of
following vehicle
• PRT = perception-reaction
time
• xo = margin of safety after
stop
• L = length of vehicle
• N =number of vehicles in
‘train’
• Taking into account the
initial spacing (s):
xf = s + xl - NL - xo
Vehicle Following
• Solving for s and substituting for xl and xf:
s = vPRT + v2/2df - v2/2dl + NL + xo
• To use: Need to specify anticipated deceleration
of the lead vehicle and the desired deceleration
of the following vehicle
2
2/1/18
Defining Deceleration
• A matter of safety
– dn = normal deceleration
– de = emergency deceleration
– ∞ = instantaneous stop
• Usually as a result of striking an object
3
2/1/18
Traffic Stream Variables
• Spacing (s) &
Concentration (k)
– Concentration also
referred to as density
– Expressed as vehicles/
length of highway
• Vehicles/mile
s = 1/k
– Since spacing and speed
is rarely uniform or
constant; s = average
spacing
Traffic Stream Variables
• Headway (h) and flow (q)
– Headway is the period of
time subsequent
vehicles pass a
stationary point
(observer)
– Flow also known as
volume
h = 1/q
• Vehicles/unit time
– Vehicles/hour
– Flow also measured at a
stationary point
4
2/1/18
Traffic Stream Equations
• Two vehicles traveling at spacing (s) and speed
(u); headway (h) = s/u.
• Substituting:
q = uk
• The fundamental traffic stream equation
– Flow equals mean speed over concentration
– Volume equals average speed over density
Traffic Stream Equations
• Flow (q), speed (u) and concentration (k) vary
constantly and simultaneously
– Cannot simply solve the equation for the missing
variable or hold one of the three variables
constant
5
2/1/18
Traffic Stream Equations
• Uniform Flow Equation
Traffic Stream Equations
• Free Flow Speed
– Free-flow conditions
• Low concentration & high speed
– At max speed and zero concentration
• FREE FLOW SPEED
6
2/1/18
Traffic Stream Equations
• Multiply both sides of the uniform flow
equation by the mean speed
Traffic Stream Equations
• Maximum Flow = Capacity
– Capacity also measured in vehicles/hour
– In certain safety regimes, capacity occurs at some
intermediate speed, not at maximum
• Up to the intermediate speed, increasing speed
increases capacity
• Beyond the intermediate speed, increased speed can
only be achieved by decreasing flow
7
2/1/18
Traffic Stream Equations
• Flow vs. Concentration
– Solve the uniform flow equation for speed in
terms of concentration
q = k u(k)
Traffic Stream Equations
• Congestion (traffic jam, flow breakdown)
occurs where there is no flow, but high
concentration
• Capacity occurs at the top of the curve
• Free flow occurs near origin
• The slope of a straight line starting at the
origin to any point on the curve = q/k, which is
speed (u)
8
2/1/18
Traffic Shock Wave
• Whenever traffic streams of varying stream
conditions meet
– A ‘Platoon’ of higher speed meets a ‘Platoon of
lower speed
• Think hydrodynamics
– Water hammer
9
2/1/18
Shock Wave Equation
10
2/1/18
11
Signalized Intersections
LOS
Methodology
Input Data Needs
Arrival Types
Arrival Types
• Best determined from field observations
• But…
Arrival Types
Pedestrian Timing
• 15th percentile pedestrian speed = 4 fps
Lane Grouping
Peak15 Flow
RTOR
• Subtract the RTOR volume for the right turn
volume
Saturation Flow Rate
Adjustment Factors
• See handout
Capacity
v/c Ratio
Delay
Progression Adjustment Factor
Progression Adjustment Factor
Uniform Delay
• Assumptions
– Uniform Arrivals
– Stable Flow
– No Initial Queue
Uniform Delay
Incremental Delay
• Non-uniform arrivals
• Temporary Cycle Failures (Random Delay)
• Sustained Periods of Over-saturation
(Saturation Delay)
Incremental Delay
Incremental Delay
Incremental Delay
• T is in ‘hours’. Evaluation period is (typically)
15 minutes. Therefore, T = 0.25
• I = 1.0 for isolated intersections
– Otherwise
Approach Delay
Vehicle Delay
LOS
Compare calculated dl to LOS table
Types of Analyses
Example
• See Handout
2/21/19
Traffic Signals
Traffic Signals
• MUTCD
– Warrants, Location of Heads, quantity, colors, visibility
• HCM
– Level of Service, Capacity, Basis of overall timing
• Construction, Operation, Maintenance
–
–
–
–
ITE Traffic Engineering Handbook
FHWA Manual of Signal Timing
PennDOT Traffic Engineering Manual (Pub. 46)
PennDOT Traffic Signal Design Handbook, (Pub. 149)
1
2/21/19
NEMA Phasing
2
2/21/19
Ring & Barrier Diagram
Protected/Prohibited
Consider Protected/Permitted Left Turn Phasing When:
• A separate turn lane is NOT present and:
– One opposing lane exists; then two or more one-hour period conflict factors (CF) need
to be greater than 35,000.
– Two opposing lanes exist; then two or more one-hour period conflict factors (CF) need
to be greater than 45,000.
• A separate turn lane present and:
– One opposing lane exists; then two or more one-hour period conflict factors (CF) need
to be greater than 50,000.
– Two opposing lanes exist; then two or more one-hour period conflict factors (CF) need
to be greater than 65,000.
Consider Protected/Prohibited Left Turn Phasing (must have a separate turn lane) When:
• One opposing lane exists; then two or more one-hour period conflict factors (CF) need to be
greater than 67,500.
• Two opposing lanes exist; then two or more one-hour period conflict factors (CF) need to be
greater than 90,000.
For dual left turn lanes Protected/Prohibited is mandatory.
Lead/Lag
• Lead/Lead Left Turn Phasing
– As a part of the standard NEMA phase rotation,
turning vehicles get the left turn arrow before the
opposing through traffic gets a circular green.
Typically, simultaneous left turn arrow indications
may be present for non-conflicting left turn
movements (e.g., Phase 1+5 or Phase 3+7).
• Lead/Lag Left Turn Phasing
– Lead/lag left turn phasing allows left turn traffic to get
a green arrow before or after opposing traffic gets a
circular green depending on traffic demand or a
progression analysis.
3
2/21/19
Yellow Trap
Motorists turning left during the permitted period may
encounter a phenomenon called the “yellow trap.” The
yellow trap occurs when a motorist making a permitted
left turn from the approach that is opposite the lag phase
observes the signal heads on their side of the intersection
turning yellow. Seeing the yellow, the motorist may
assume that the opposing through traffic is also receiving
a yellow and is in the process of stopping whereas, in
reality, the opposing through traffic still has a circular
green that is running concurrently with the lagging left
turn. This set of circumstances could induce the motorist
to turn left into an oncoming vehicle.
Phasing
• Split Phasing
• Overlap
– Right Turn Overlap
Phasing
•
•
•
•
Two Phase
Three Phase
Four Phase
Five to eight phase
4
2/21/19
Cycle Length
•
•
•
•
45 to 120 seconds (PA preference)
Fixed time
Semi actuated
Fully actuated
Minimum Green Times
Passage
5
2/21/19
Maximum Green Time
Volume Density
Dilemma Zone
6
2/21/19
Loop Setback
Operation & Phasing
7
2/21/19
Visors
8
2/21/19
9
2/21/19
Control
•
•
•
•
Time Based Coordination (TBC)
Interconnection
Centralized/Closed Loop System
Traffic Adaptive
10
Signalized Intersections
LOS
Methodology
Input Data Needs
Arrival Types
Arrival Types
• Best determined from field observations
• But…
Arrival Types
Pedestrian Timing
• 15th percentile pedestrian speed = 4 fps
Lane Grouping
Peak15 Flow
RTOR
• Subtract the RTOR volume for the right turn
volume
Saturation Flow Rate
Adjustment Factors
• See handout
Capacity
v/c Ratio
Delay
Progression Adjustment Factor
Progression Adjustment Factor
Uniform Delay
• Assumptions
– Uniform Arrivals
– Stable Flow
– No Initial Queue
Uniform Delay
Incremental Delay
• Non-uniform arrivals
• Temporary Cycle Failures (Random Delay)
• Sustained Periods of Over-saturation
(Saturation Delay)
Incremental Delay
Incremental Delay
Incremental Delay
• T is in ‘hours’. Evaluation period is (typically)
15 minutes. Therefore, T = 0.25
• I = 1.0 for isolated intersections
– Otherwise
Approach Delay
Vehicle Delay
LOS
Compare calculated dl to LOS table
Types of Analyses
Example
• See Handout
Highway Capacity Manual 2000
EXHIBIT 16-7. ADJUSTMENT FACTORS FOR SATURATION FLOW RATE a
Factor
Lane width
Formula
f w = 1+
Heavy
vehicles
Grade
f HV =
fp =
f bb =
Lane
utilization
Left turns
30
(
%G
200
Pedestrianbicycle
blockage
18Nm
3600
N
N−
14.4NB
3600
N
fa = 0.900 in CBD
fa = 1.000 in all other areas
fLU = vg/(v g1N)
Protected phasing:
Exclusive lane:
fLT = 0.95
Shared lane:
f LT =
Right turns
)
100 + %HV E T − 1
N − 0.1−
Bus blockage
Type of area
(W − 12)
100
f g = 1−
Parking
Definition of Variables
W = lane width (ft)
% HV = % heavy vehicles for
lane group volume
Input Parameters
Notes
W ≥ 8.0
If W > 16, a two-lane analysis
may be considered
ET = 2.0 pc/HV
% G = % grade on a lane
group approach
-6 ≤ % G ≤ +10
Negative is downhill
N = number of lanes in lane
group
Nm = number of parking
maneuvers/h
N = number of lanes in lane
group
NB = number of buses
stopping/h
0 ≤ Nm ≤ 180
fp ≥ 0.050
fp = 1.000 for no parking
Lane Grouping &
Demand Flow
Rate
Saturation Flow
- Adjustment
Factors
Capacity & v/c
Performance
Measures
0 ≤ NB ≤ 250
fbb ≥ 0.050
vg = unadjusted demand flow
rate for the lane group,
veh/h
vg1 = unadjusted demand flow
rate on the single lane in
the lane group with the
highest volume
N = number of lanes in the
lane group
P LT = proportion of LTs in
See Exhibit C16-1, Appendix
C, for nonprotected phasing
lane group
alternatives
1
1.0 + 0.05PLT
Exclusive lane:
fRT = 0.85
Shared lane:
fRT = 1.0 – (0.15)PRT
Single lane:
fRT = 1.0 – (0.135)PRT
LT adjustment:
fLpb = 1.0 – PLT(1 – ApbT)
(1 – PLTA)
RT adjustment:
fRpb = 1.0 – PRT (1 – ApbT)
(1 – PRTA)
P RT = proportion of RTs in
lane group
fRT ≥ 0.050
P LT = proportion of LTs in lane Refer to Appendix D for stepby-step procedure
group
A pbT = permitted phase
adjustment
P LTA = proportion of LT
protected green over
total LT green
P RT = proportion of RTs in
lane group
P RTA = proportion of RT
protected green over
total RT green
Note:
See Chapter 10, Exhibit 10-12, for default values of base saturation flow rates and variables used to derive adjustment factors.
a. The table contains formulas for all adjustment factors. However, for situations in which permitted phasing is involved, either
by itself or in combination with protected phasing, separate tables are provided, as indicated in this exhibit.
16-11
Chapter 16 - Signalized Intersections
Methodology
Highway Capacity Manual 2000
EXAMPLE PROBLEM 1
The Intersection
The intersection of Third Avenue (NB/SB) and Main Street (EB/WB)
is located in the central business district (CBD) of a small urban area. Intersection
geometry and flow characteristics are shown on the Input Worksheet.
The Question
What are the delay and peak-hour LOS of this intersection?
The Facts
√ EB and WB HV = 5 percent,
√ NB and SB HV = 8 percent,
√ PHF = 0.90,
√ Two-phase signal,
√ NB-SB green = 36 s,
√ EB-WB green = 26 s,
√ Yellow = 4 s,
√
√
√
√
√
√
√
Third Avenue has two lanes, one in each direction,
Main Street has four lanes, two in each direction,
No parking at intersection,
Pedestrian volume = 100 p/h, all approaches,
Bicycle volume = 20 bicycles/h, all approaches,
Movement lost time = 4 s, and
Level terrain.
Comments
√ Assume crosswalk width = 10 ft for all approaches,
√ Assume base saturation flow rate = 1,900 pc/h/ln,
√ Assume ET = 2.0,
√ No buses, and
√ 70.0-s cycle length, with green times given.
Steps
p
1h
*
* 70 s = 1. 944 p
h 3,600 s
1.
Pedestrians/cycle.
2.
Minimum effective green time
required for pedestrians (use
Equation 16-2).
Gp = 3.2 +
3.
Compare minimum effective
green time required for
pedestrians with actual
effective green.
Gp (Main) = 26 s, which is >11.2 s
4.
Proportions of left and right
turns.
Proportions of left- and right-turn traffic are found by
dividing the appropriate turning volumes by the total
lane group volume.
65
PLT (EB) =
= 0.090
65 + 620 + 35
5.
Lane width adjustment factor
(use Exhibit 16-7).
(W − 12)
30
(11− 12)
f w (EB) = 1+
= 0. 967
30
6.
Heavy-vehicle adjustment
factor (use Exhibit 16-7).
fHV =
100
L
+ 0.27Nped
4.0
30
Gp (Main) = 3.2 +
+ 0.27(1.944) = 11.2 s
4.0
44
Gp (Third) = 3.2 +
+ 0.27(1.944) = 14.7 s
4.0
Gp (Third) = 36 s, which is >14.7 s
f w = 1+
100
100 + % HV(E T − 1)
fHV (EB) =
7.
Chapter 16 - Signalized Intersections
Example Problems
Percent grade adjustment
factor (use Exhibit 16-7).
16-38
100
= 0. 952
100 + 5(2.0 − 1)
0% grade, fg = 1.000
Highway Capacity Manual 2000
8.
Parking adjustment factor
(use Exhibit 16-7).
No parking maneuvers, fp = 1.000
9.
Bus blockage adjustment
factor (use Exhibit 16-7).
No buses stopping, fbb = 1.000
10. Area type adjustment factor
(use Exhibit 16-7).
For CBD, fa = 0.900
11. Lane utilization adjustment
factor (use Exhibit 16-7).
Refer to Exhibit 10-23. This factor is applied to
establish the conditions in the worst lane within each
lane group. Otherwise, the results would reflect the
average of all lanes of the defined lane groups. Use
fLU = 0.950 for EB and WB approaches, and fLU =
1.000 for NB and SB approaches.
12. Left-turn adjustment factor.
The left turn is permitted, hence a special procedure
is needed. The EB and WB left turns are opposed
by multilane approaches. The supplemental
worksheet for multilane approaches is used. The
NB and SB left turns are opposed by single-lane
approaches. The supplemental worksheet for a
single-lane approach is used.
13. Right-turn adjustment factor
(use Exhibit 16-7).
For NB and SB single-lane approaches: fRT = 1.0 –
0.135PRT
For EB and WB shared-lane approaches: fRT = 1.0–
0.150PRT
14. Left-turn pedestrian/bicycle
adjustment factor.
Supplemental worksheet for pedestrian-bicycle
effects is used.
15. Right-turn pedestrian/bicycle
adjustment factor.
Supplemental worksheet for pedestrian-bicycle
effects is used.
16. Saturation flow.
s = so N fw fHV fg fp fbb fLU fa fLT fRT fLpb fRpb
s(EB) = 1900 * 2 * 0.967 * 0.952 * 1.000 * 1.000 *
1.000 * 0.900 * 0.950 * 0.716 * 0.993 * 0.997 * 0.992
= 2103 veh/h
17. Lane group capacity.
c = s(g/C)
18. v/c ratio.
c(EB) = 2103(0.371) = 780 veh/h
800
v/c(EB) =
= 1.026
780
19. Determine critical lane group
in each timing phase.
20. Flow ratio of critical lane
groups.
The lane group with the highest v/c ratio in a phase
is considered the critical lane group. In this case,
EB and SB lane groups are critical in Phases 1 and
2, respectively.
800
v/s(EB) =
= 0.380
2103
667
v/s(SB) =
= 0.410
1625
21. Sum of critical flow ratios.
Yc = 0.380 + 0.410 = 0.790
22. Critical flow rate to capacity
ratio.
Xc =
Yc * C
C–L
0.790(70.0)
Xc =
= 0.892
70.0 – 8
16-39
Chapter 16 - Signalized Intersections
Example Problems
Highway Capacity Manual 2000
2
23. Uniform delay.
g
0. 50C 1−
C
d1 =
g
1− min(1, X)
C
0. 50(70.0)(1− 0. 371)2
d1(EB) =
= 22.015 s/veh
1− 0. 371(1.0)
24. Incremental delay.
d2 = 900T (X − 1) + (... )
[
[
]
]
d2 (EB) = 900(0. 25) (1.026 − 1) + (... ) =
25. Progression adjustment factor
(use Exhibit 16-12).
39.011 s/veh
PF (EB) = 0.926
d = d1PF + d2 + d3
d (EB) = 22.015(0.926) + 39.011 + 0 = 59.4 s/veh
∑ (d A )(v A )
dI =
∑ vA
26. Lane group delay.
27. Intersection delay.
dI =
(59.4 * 800) + (31.0 * 833) + (14.4 * 466) + (21.9 * 667)
(800 + 833 + 466 + 667)
= 34.2 s/veh
28. LOS by lane group,
approach, and intersection.
LOS (EB lane group) = E
LOS (EB approach) = E
LOS Intersection = C
The calculation results are summarized as follows.
Direction/
LnGrp
EB/LTR
WB/LTR
NB/LTR
SB/LTR
v/c
Ratio
g/C
Ratio
Unif
Delay d1
1.026 0.371
22.015
0.842 0.371
20.138
0.561 0.514
11.617
0.799 0.514
14.028
Intersection Delay = 34.2 s/veh
Progr
Fact PF
0.926
1.111
1.000
1.000
Lane
Grp
Cap
780
989
830
835
Cal
Term k
0.5
0.5
0.5
0.5
Incr
Delay d2
Lane
Lane
Grp
Grp
Delay
LOS
39.011
59.4
E
8.647
31.0
C
2.734
14.4
B
7.882
21.9
C
Intersection LOS = C
Delay
by App
LOS by
App
59.4
31.0
14.4
21.9
E
C
B
C
Alternatives
Two alternatives are considered: a new lane utilization adjustment factor and new
signal timing.
The purpose of the lane utilization adjustment factor (fLU) is to account for uneven
distribution of traffic in multilane roadways, and it is reflected in saturation flow rates.
Typically, traffic volume is evenly distributed between lanes at high v/c ratios, and the
lane utilization adjustment factor is close to 1.000. In this analysis, f LU is only applicable to
Main Street because it has multiple lanes. v/c ratios of 1.026 and 0.842 are considered
high, and it is assumed that traffic volume is evenly distributed, with f LU = 1.000.
The performance is reassessed using fLU = 1.000 and the results are summarized as
follows.
Direction/
Ln Grp
v/c
Ratio
g/C
Ratio
Unif
Delay d1
EB/LTR
WB/LTR
NB/LTR
SB/LTR
0.945
0.798
0.561
0.799
0.371
0.371
0.514
0.514
21.323
19.671
11.617
14.028
Intersection Delay = 27.7 s/veh
Chapter 16 - Signalized Intersections
Example Problems
16-40
Progr
Factor
PF
0.926
1.111
1.000
1.000
Ln Grp
Capacity
847
1044
830
835
Cal
Term k
Incr
Delay d2
Ln Grp
Delay
Ln Grp
LOS
Delay
by App
LOS
by App
0.5
0.5
0.5
0.5
20.134
6.365
2.734
7.882
39.9
28.2
14.4
21.9
D
C
B
C
39.9
28.2
14.4
21.9
D
C
B
C
Intersection LOS = C
Highway Capacity Manual 2000
The assumption of fLU = 1.000 has reduced the delay from 34.2 s/veh to 27.7 s/veh.
The other alternative is to optimize the operation by reallocating green times without
changing fLU.
As shown in the calculation results, currently the v/c ratios between critical lane
groups are not balanced. The v/c ratio of the EB lane group is much higher than that of
the SB lane group. This imbalance results in much higher delay experienced by one
critical lane group than by the other.
A new signal timing is introduced by reallocating 1.0 s to the east-west phase from the
north-south phase. The resulting signal timing is 27.0 s for the east-west phase and 35.0 s
for the north-south phase.
The intersection operation is reassessed with the new timing, and the results are
summarized as follows.
Direction/
Ln Grp
v/c
Ratio
g/C
Ratio
Unif
Delay d1
EB/LTR
WB/LTR
NB/LTR
SB/LTR
0.972 0.386
21.118
0.807 0.386
19.165
0.578 0.500
12.307
0.821 0.500
14.843
Intersection Delay = 29.8 s/veh
Progr
Factor
PF
Ln Grp
Cap
Cal
Term k
Incr
Delay
d2
0.926
1.111
1.000
1.000
823
1032
806
812
0.5
0.5
0.5
0.5
25.265
6.766
3.011
9.132
Ln Grp
Delay
Ln Grp
LOS
44.8
D
28.1
C
15.3
B
24.0
C
Intersection LOS = C
Delay
by App
LOS by
App
47.9
28.1
17.3
34.0
D
C
B
C
After reallocation of green times, v/c ratios for critical lane groups are more balanced,
and the overall intersection performance (in terms of delay) has improved from 34.2 s/veh
to 29.8 s/veh.
16-41
Chapter 16 - Signalized Intersections
Example Problems
Highway Capacity Manual 2000
Example Problem 1
INPUT WORKSHEET
General Information
Analyst
Agency or Company
Date Performed
Analysis Time Period
Site Information
WLL
_______________________________
CEI
_______________________________
4/12/99
_______________________________
4-6 PM
_______________________________
Intersection
Area Type
Jurisdiction
Analysis Year
Third Avenue/Main Street
_____________________________
X CBD
q
q Other
_____________________________
1999
_____________________________
Intersection Geometry
15 ft
= Pedestrian Button
Street
0%
Third Avenue
grade=
= Lane Width
Show North Arrow
grade=
11 ft
grade=
100(20)
100(20)
11 ft
= Through
0%
100(20)
11 ft
= Right
11 ft
= Left
= Through + Right
100(20)
0%
= Left + Through
Main Street
Street
= Left + Right
grade=
15 ft
= Left + Through + Right
0%
Volume and Timing Input
EB
Volume, V (veh/h)
% heavy vehicles, % HV
Peak-hour factor, PHF
Pretimed (P) or actuated (A)
Start-up lost time, l1 (s)
Extension of effective green time, e (s)
Arrival type, AT
Approach pedestrian volume,2 vped (p/h)
Approach bicycle volume,2 vbic (bicycles/h)
Parking (Y or N)
Parking maneuvers, Nm (maneuvers/h)
Bus stopping, NB (buses/h)
Min. timing for pedestrians,3 Gp (s)
LT
65
5
TH
620
5
0.90
P
WB
RT1
35
5
4
100
20
N
0
0
11.2
LT
30
5
TH
RT1
700 20
5
5
0.90
P
NB
LT
30
8
2
100
20
N
0
0
11.2
TH
370
8
0.90
P
SB
RT1
20
8
3
100
20
N
0
0
14.7
LT
40
8
TH
510
8
0.90
P
3
100
20
N
0
0
14.7
Signal Phasing Plan
D
I
A
G
R
A
M
Timing
Ø1
Ø2
Ø3
Ø4
G = 26.0
Y = 4.0
G = 36.0
Y = 4.0
G=
Y=
G=
Y=
Protected turns
Ø5
G=
Y=
Permitted turns
Pedestrian
Ø6
G=
Y=
Notes
1. RT volumes, as shown, exclude RTOR.
2. Approach pedestrian and bicycle volumes are those that conflict with right turns from the subject approach.
3. Refer to Equation 16-2.
Chapter 16 - Signalized Intersections
Example Problems
16-42
Ø7
G=
Y=
Ø8
G=
Y=
70.0 s
Cycle length, C = _____
RT1
50
8
Highway Capacity Manual 2000
Example Problem 1
VOLUME ADJUSTMENT AND SATURATION FLOW RATE WORKSHEET
General Information
Example Problem 1
Project Description______________________________________________________________________________________
Volume Adjustment
EB
Volume, V (veh/h)
LT
TH
65
620
Peak-hour factor, PHF
Adjusted flow rate, vp = V/PHF (veh/h)
WB
689
SB
RT
LT
TH
RT
LT
TH
RT
LT
TH
RT
35
30
700
20
30
370
20
40
510
50
0.90
72
NB
0.90
39
33
778
0.90
22
33
411
0.90
22
44
567
56
Lane group
Adjusted flow rate in lane group, v (veh/h)
Proportion1 of LT or RT (PLT or PRT)
800
0.090
-
833
0.049 0.040
-
466
0.027 0.071
-
667
0.048 0.067
-
0.083
Saturation Flow Rate (see Exhibit 16-7 to determine adjustment factors)
Base saturation flow, so (pc/h/ln)
1900
1900
1900
1900
2
2
1
1
Lane width adjustment factor, fw
0.967
0.967
1.100
1.100
Heavy-vehicle adjustment factor, fHV
0.952
0.952
0.926
0.926
Grade adjustment factor, fg
1.000
1.000
1.000
1.000
Parking adjustment factor, fp
1.000
1.000
1.000
1.000
Bus blockage adjustment factor, fbb
1.000
1.000
1.000
1.000
Area type adjustment factor, fa
0.900
0.900
0.900
0.900
Lane utilization adjustment factor, fLU
0.950
0.950
1.000
1.000
Left-turn adjustment factor, fLT
0.716
0.901
0.937
0.951
Right-turn adjustment factor, fRT
0.993
0.996
0.994
0.989
Left-turn ped/bike adjustment factor, fLpb
0.997
0.998
0.999
0.998
Right-turn ped/bike adjustment factor, fRpb
0.992
0.995
0.996
0.994
2103
2665
1614
1625
Number of lanes, N
Adjusted saturation flow, s (veh/h)
s = so N fw fHV fg fp fbb fa fLU fLT fRT fLpb fRpb
Notes
1. PLT = 1.000 for exclusive left-turn lanes, and PRT = 1.000 for exclusive right-turn lanes. Otherwise, they are equal to the proportions
of turning volumes in the lane group.
16-43
Chapter 16 - Signalized Intersections
Example Problems
Highway Capacity Manual 2000
Example Problem 1
SUPPLEMENTAL WORKSHEET FOR PERMITTED LEFT TURNS
OPPOSED BY SINGLE-LANE APPROACH
General Information
Example Problem 1
Project Description _____________________________________________________________________________________
Input
EB
Cycle length, C (s)
WB
NB
SB
70.0
Total actual green time for LT lane group,1 G (s)
36.0
Effective permitted green time for LT lane group,1 g (s)
36.0
36.0
Opposing effective green time, go (s)
36.0
36.0
1
36.0
Number of lanes in LT lane group,2 N
1
Adjusted LT flow rate, vLT (veh/h)
33
44
Proportion of LT volume in LT lane group, PLT
0.071
0.067
Proportion of LT volume in opposing flow, PLTo
0.067
0.071
Adjusted flow rate for opposing approach, vo (veh/h)
667
466
Lost time for LT lane group, tL
4
4
Computation
LT volume per cycle, LTC = vLTC/3600
Opposing flow per lane, per cycle,
volc = voC/3600 (veh/C/ln)
Opposing platoon ratio, Rpo (refer to Exhibit 16-11)
0.629
gf ≤ g (except exclusive
gf = G[e–0.860(LTC )] – tL
left-turn lanes)3
Opposing queue ratio, qro = max[1 – Rpo(go/C), 0]
0.642
0.856
12.969
9.061
1.00
1.00
14.779
12.505
0.486
0.486
12.201
8.328
gu = g – gf if gq < gf
21.221
23.495
n = max[(gq – gf)/2, 0]
0
0
PTHo = 1 – PLTo
0.933
0.929
EL1 (refer to Exhibit C16-3)
2.7
2.2
gq = 4.943volc0.762qro1.061 – tL
gq ≤ g
gu = g – gq if gq ≥ gf, or
EL2 = max[(1 – PTHon)/PLTo, 1.0]
1.0
1.0
fmin = 2(1 + PLT)/g
0.060
0.059
gdiff = max[gq – gf, 0] (except when left-turn volume
is 0)4
0
0
0.937
0.951
fLT = fm = [gf/g] +
(fmin ≤ fm ≤ 1.00)
gdiff/g
gu/g
1 + PLT(EL1 – 1) + 1 + PLT(EL2 – 1)
Notes
1. Refer to Exhibits C16-4, C16-5, C16-6, C16-7, and C16-8 for case-specific parameters and adjustment factors.
2. For exclusive left-turn lanes, N is equal to the number of exclusive left-turn lanes. For shared left-turn lanes, N is equal to the sum of
the shared left-turn, through, and shared right-turn (if one exists) lanes in that approach.
3. For exclusive left-turn lanes, gf = 0, and skip the next step. Lost time, tL, may not be applicable for protected-permitted case.
4. If the opposing left-turn volume is 0, then gdiff = 0.
Chapter 16 - Signalized Intersections
Example Problems
16-44
Highway Capacity Manual 2000
Example Problem 1
SUPPLEMENTAL WORKSHEET FOR PERMITTED LEFT TURNS
OPPOSED BY MULTILANE APPROACH
General Information
Example Problem 1
Project Description _____________________________________________________________________________________
Input
EB
Cycle length, C (s)
WB
NB
SB
70.0
Total actual green time for LT lane group,1 G (s)
26.0
26.0
Effective permitted green time for LT lane group,1 g (s)
26.0
26.0
Opposing effective green time, go (s)
26.0
26.0
Number of lanes in LT lane group,2 N
2
2
Number of lanes in opposing approach, No
2
2
Adjusted LT flow rate, vLT (veh/h)
72
Proportion of LT volume in LT lane group,3 PLT
0.090
Adjusted flow rate for opposing approach, vo (veh/h)
833
Lost time for LT lane group, tL
4
33
0.040
800
4
Computation
LT volume per cycle, LTC = vLTC/3600
1.400
0.642
Opposing lane utilization factor, fLUo (refer to Volume
Adjustment and Saturation Flow Rate Worksheet)
0.950
0.950
8.525
8.187
4.461
9.684
Opposing flow per lane, per cycle
volc =
voC
3600NofLUo
(veh/C/ln)
0.717
gf = G[e–0.882(LTC
left-turn lanes)1, 4
)]
– tL gf ≤ g (except for exclusive
Opposing platoon ratio, Rpo (refer to Exhibit 16-11)
0.67
1.33
Opposing queue ratio, qro = max[1 – Rpo(go/C), 0]
0.751
0.506
11.303
8.027
gu = g – gf if gq < gf
14.697
16.316
EL1 (refer to Exhibit C16-3)
3.3
volcqro
gq = 0.5 – [volc(1 – qro)/go] – tL, volc(1 – qro)/go ≤ 0.49
(note case-specific parameters)1
gu = g – gq if gq ≥ gf, or
PL = PLT
(N – 1)g
1+
(gf + gu/EL1 + 4.24)
(except with multilane subject approach)5
fmin = 2(1 + PL)/g
fm = [gf/g] + [gu/g]
1
1 + PL(EL1 – 1)
, (fmin ≤ fm ≤ 1.00)
fLT = [fm + 0.91(N – 1)]/N (except for permitted left
turns)6
3.2
0.268
0.095
0.098
0.084
0.521
0.892
0.716
0.901
Notes
1. Refer to Exhibits C16-4, C16-5, C16-6, C16-7, and C16-8 for case-specific parameters and adjustment factors.
2. For exclusive left-turn lanes, N is equal to the number of exclusive left-turn lanes. For shared left-turn lanes, N is equal to the sum of the
shared left-turn, through, and shared right-turn (if one exists) lanes in that approach.
3. For exclusive left-turn lanes, PLT = 1.
4. For exclusive left-turn lanes, gf = 0, and skip the next step. Lost time, tL, may not be applicable for protected-permitted case.
5. For a multilane subject approach, if PL ≥ 1 for a left-turn shared lane, then assume it to be a de facto exclusive left-turn lane and redo the
calculation.
6. For permitted left turns with multiple exclusive left-turn lanes fLT = fm.
16-45
Chapter 16 - Signalized Intersections
Example Problems
Highway Capacity Manual 2000
Example Problem 1
SUPPLEMENTAL WORKSHEET FOR PEDESTRIAN-BICYCLE EFFECTS
ON PERMITTED LEFT TURNS AND RIGHT TURNS
General Information
Example Problem 1
Project Description _____________________________________________________________________________________
Permitted Left Turns
Effective pedestrian green time,1,2 gp (s)
Conflicting pedestrian volume,1 vped (p/h)
vpedg = vped (C/gp)
OCCpedg = vpedg/2000 if (vpedg ≤ 1000) or
OCCpedg = 0.4 + vpedg/10,000 if (1000 < vpedg ≤ 5000)
Opposing queue clearing green,3,4 gq (s)
Effective pedestrian green consumed by opposing
vehicle queue, gq/gp; if gq ≥ gp then fLpb = 1.0
OCCpedu = OCCpedg [1 – 0.5(gq/gp)]
Opposing flow rate,3 vo (veh/h)
OCCr = OCCpedu [e–(5/3600)vo]
Number of cross-street receiving lanes,1 Nrec
Number of turning lanes,1 Nturn
ApbT = 1 – OCCr if Nrec = Nturn
ApbT = 1 – 0.6(OCCr) if Nrec > Nturn
Proportion of left turns,5 PLT
Proportion of left turns using protected phase,6 PLTA
fLpb = 1.0 – PLT(1 – ApbT)(1 – PLTA)
EB
WB
NB
26.0
100
269
26.0
100
269
36.0
100
194
SB
36.0
100
194
0.135
0.135
0.097
0.097
11.303
8.027
12.201
8.328
0.435
0.309
0.339
0.231
0.106
833
0.114
800
0.081
667
0.086
466
0.033
1
1
0.038
1
1
0.032
2
1
0.045
2
1
0.967
0.962
0.981
0.973
0.090
0.040
0.071
0.067
0
0.997
0
0.998
0
0.999
0
0.998
Permitted Right Turns
Effective pedestrian green time,1,2 gp (s)
Conflicting pedestrian volume,1 vped (p/h)
Conflicting bicycle volume,1,7 vbic (bicycles/h)
vpedg = vped(C/gp)
OCCpedg = vpedg/2000 if (vpedg ≤ 1000), or
OCCpedg = 0.4 + vpedg/10,000 if (1000 < vpedg ≤ 5000)
Effective green,1 g (s)
vbicg = vbic(C/g)
OCCbicg = 0.02 + vbicg/2700
OCCr = OCCpedg + OCCbicg – (OCCpedg)(OCCbicg)
Number of cross-street receiving lanes,1 Nrec
Number of turning lanes,1 Nturn
ApbT = 1 – OCCr if Nrec = Nturn
ApbT = 1 – 0.6(OCCr) if Nrec > Nturn
Proportion of right turns,5 PRT
Proportion of right turns using protected phase,8 PRTA
fRpb = 1.0 – PRT(1 – ApbT)(1 – PRTA)
26.0
26.0
36.0
36.0
100
20
269
100
20
269
100
20
194
100
20
194
0.135
0.135
0.097
0.097
26.0
54
0.040
0.170
1
1
26.0
54
0.040
0.170
1
1
36.0
39
0.034
0.128
2
1
36.0
39
0.034
0.128
2
1
0.830
0.830
0.923
0.923
0.049
0
0.992
0.027
0
0.995
0.048
0
0.996
0.083
0
0.994
Notes
1. Refer to Input Worksheet.
2. If intersection signal timing is given, use Walk + flashing Don't Walk (use G + Y if
no pedestrian signals). If signal timing must be estimated, use (Green Time – Lost
Time per Phase) from Quick Estimation Control Delay and LOS Worksheet.
3. Refer to supplemental worksheets for left turns.
4. If unopposed left turn, then gq = 0, vo = 0, and OCCr = OCCpedu = OCCpedg.
Chapter 16 - Signalized Intersections
Example Problems
16-46
5. Refer to Volume Adjustment and Saturation Flow Rate Worksheet.
6. Ideally determined from field data; alternatively, assume it equal to
(1 – permitted phase fLT)/0.95.
7. If vbic = 0 then vbicg = 0, OCCbicg = 0, and OCCr = OCCpedg.
8. PRTA is the proportion of protected green over the total green, gprot/(gprot
+ gperm). If only permitted right-turn phase exists, then PRTA = 0.
Highway Capacity Manual 2000
Example Problem 1
CAPACITY AND LOS WORKSHEET
General information
Example Problem 1
Project Description _____________________________________________________________________________________
Capacity Analysis
Phase number
Phase type
1
P
1
P
2
P
2
P
Lane group
Adjusted flow rate, v (veh/h)
Saturation flow rate, s (veh/h)
Lost time, tL (s), tL = l1 + Y – e
Effective green time, g (s), g = G + Y – tL
Green ratio, g/C
Lane group capacity,1 c = s(g/C), (veh/h)
v/c ratio, X
Flow ratio, v/s
Critical lane group/phase (√)
Sum of flow ratios for critical lane groups, Yc
Yc = ∑ (critical lane groups, v/s)
Total lost time per cycle, L (s)
Critical flow rate to capacity ratio, Xc
Xc = (Yc)(C)/(C – L)
800 833 466
2103 2665 1614
4
4
4
26.0 26.0 36.0
0.371 0.371 0.514
780 989 830
1.026 0.842 0.561
0.380
√
667
1625
4
36.0
0.514
835
0.799
0.410
√
0.790
8
0.892
Lane Group Capacity, Control Delay, and LOS Determination
EB
WB
NB
SB
Lane group
Adjusted flow rate,2 v (veh/h)
Lane group capacity,2 c (veh/h)
v/c ratio,2 X = v/c
Total green ratio,2 g/C
0.50 C [1 – (g/C)]2
Uniform delay, d1 = 1 – [min(1, X)g/C] (s/veh)
Incremental delay calibration,3 k
Incremental delay,4 d2
d2 = 900T [(X – 1) + (X – 1)2 + 8kIX ](s/veh)
cT
Initial queue delay, d3 (s/veh) (Appendix F)
Uniform delay, d1 (s/veh) (Appendix F)
Progression adjustment factor, PF
Delay, d = d1(PF) + d2 + d3 (s/veh)
LOS by lane group (Exhibit 16-2)
Delay by approach, dA = ∑(d)(v) (s/veh)
∑v
LOS by approach (Exhibit 16-2)
Approach flow rate, vA (veh/h)
Intersection delay, dI = ∑(dA)(vA) (s/veh)
∑vA
800
833
466
667
780
1.026
0.371
989
0.842
0.371
830
0.561
0.514
835
0.799
0.514
22.015
20.138
11.617
14.028
0.5
0.5
0.5
0.5
39.011
8.647
2.734
7.882
0
0
0
1.111
31.0
C
1.000
14.4
B
1.000
21.9
C
59.4
31.0
14.4
21.9
E
800
C
833
B
466
C
667
0
0.926
59.4
E
34.2
Intersection LOS (Exhibit 16-2)
C
Notes
1.
2.
3.
4.
For permitted left turns, the minimum capacity is (1 + PL)(3600/C).
Primary and secondary phase parameters are summed to obtain lane group parameters.
For pretimed or nonactuated signals, k = 0.5. Otherwise, refer to Exhibit 16-13.
T = analysis duration (h); typically T = 0.25, which is for the analysis duration of 15 min.
I = upstream filtering metering adjustment factor; I = 1 for isolated intersections.
16-47
Chapter 16 - Signalized Intersections
Example Problems
1/23/18
Terms
• Kinematics: study of motion irrespective of the
forces that cause it
– Kinetics: accounts for the forces
• Motion
– Rectilinear of Curvilinear
• Absolute or Relative
– The rectilinear position of x is measured in units of
length
• Displacement: difference in position between two
instances
Velocity
The Displacement of a particle x divided by the
time over which it occurs.
• Speed
– Scalar
– Equals the magnitude of the velocity (a vector)
• In roadway design, they are interchangeable
1 MPH = 1.47 FPS
Acceleration
The rate of change of velocity with respect to
time.
– Deceleration is negative acceleration
– AASHTO Design Value = 11.2 ft/s2
1
1/23/18
Braking Distance
v02 – v2
D=
------------------2g(f +/- G)
G: grade/100%
g = 32.2 fps
Braking Distance
• AASHTO
d = V2/30(f +/- G)
in Miles Per Hour (MPH)
2
1/23/18
Friction (f)
• Dimensionless representation of the tirepavement interaction.
• Same for all vehicles (cars/trucks/buses/etc.)
• Varies with environmental conditions.
• Range
– Dry Pavement = 0.6 to 0.8
– Wet Pavement = 0.3 to 0.4
– Ice/Snow = 0.05 to 0.2
Friction (f)
• Customary values (book)
– Dry = 0.6
– Wet = 0.3
• AASHTO Design Value = 0.34
Fundamental Assumptions
• Tire-Pavement Interaction (friction)
– Measured with a fixed rubber tire sliding over the
pavement surface.
– Two ASTM Standards
• ASTM
–
–
–
–
Worldwide
Consensus
Peer Reviewed
Voluntary
3
1/23/18
ASTM E274-11
• Standard Test Method for Skid Resistance of
Paved Surfaces Using a Full-Scale Tire
12.Precision and Bias
12.1 The relationship of observed SN (skid number) units
to some “true” value of locked-wheel sliding friction
has not been established at this time.
ASTM E445-88
• Standard Test Method for Stopping Distance
on Paved Surfaces Using a Passenger Vehicle
Equipped with Full-Scale Tires
– Reapproved 2008
12.Precision and Bias
12.1 The relationship of observed SDN (stopping-distance
number) units to some “true” value of locked-wheel
sliding friction has not been established at this time.
Tire-Pavement Interaction (friction)
• Dependent on many factors…
–
–
–
–
–
–
–
Wet or dry
Temperature
Age of pavement
Type of surface
Presence of debris
Tire
Vehicle load
When testing was performed, if any, does it replicate
actual conditions?
4
1/23/18
Tire-Pavement Interaction (friction)
• Range of values
– AASHTO (Design) – 0.34 (wet pavement)
Tire-Pavement Interaction (friction)
5
1/23/18
SSSD = 1.47(V)(t) + V2/30 (f+g)
v=speed (mph)
t=PRT
f=friction
g=grade (ft/ft; up+; down-)
Curvilinear Motion
• Vehicles round curves….
• Side Friction Factor (fs)
e + fs = v2/gR (1 - fs e )
– e = super-elevation…curve banking (ft/ft)
– R = Radius of Horizontal Curve (feet)
– For roadway design: fs e = 0
Curvilinear Motion
• AASHTO
f = (V2/15R) – e
…again, V in MPH!
6
1/23/18
Visual Acuity = 2arctan(L/2D)
Human Factors
• The Equations of Motion do NOT take into
account driver performance!
• Total Stopping Distance includes:
– Braking Distance (equations of motion)
• What happens the moment are brakes are applied
+
– Perception-Reaction Time
7
1/23/18
Perception-Reaction Time
• The time it takes for our brain to process
information
– To recognize the need to stop
– To tell our foot to apply pressure to the brake
– IT CAN BE MORE TIME, A GREATER DISTANCE
TRAVELED, THAN THE ACTUAL BRAKING
DISTANCE.
– Design is based on total Stopping Distance
• Including PRT!
1.Perception
2.Identification
3.Emotion
4.Reaction/Volition
Perception-Reaction Time
• Essentially response
time to anticipated
braking
• Effected by
–
–
–
–
–
–
–
–
–
–
Driver capability
Driver education
Driver attentiveness
Age
Medical condition
Alcohol/drug use
Fatigue
Sleep deprivation
Emotional state
etc……..
8
1/23/18
Perception-Reaction Time
• Also effected by
– Roadway stimulus
– Amount of information to be processed
– Complexity of the decision making
•
•
•
•
Standard control devices (MUTCD)
Rules of the road
Roadside ‘clutter’
Driveway and intersection spacing
Perception-Reaction Time
• Johannson & Rumar, 1971
– Measured response times
• Design Value
– 85th percentile driver
• One, unexpected, information content (bit)
2.5 seconds
9
1/23/18
• SAE Studies, since 1971
–0.5 to 2.7 seconds
Design Vehcile
10
1/23/18
11
1/23/18
12
8/27/19
What Exactly Are We Talking About
• The very Essence of our freedom?
– Where we live
– Where we work
– Where we shop
– Where we play
– Where we go to school
• Its all about choices…
•
…and transportation provides the
ability to make those choices.
Point A to Point B
• Overcoming the friction of geographic space
The Growth of the Country
• The westward expansion
• The Industrial Revolution
• WW2
Success dependent on transportation
1
8/27/19
Transportation Systems
• Consist of:
– Fixed Facilities
– Flow Entities
– Control Systems
• To move people and goods:
– Efficiently
– Timely
– Safely
Fixed Facilities
• Components that are fixed in time and space
– Links
• Roads, tracks, pipelines, etc.
– Nodes
• Interchanges, Intersections, terminals, stations,
harbors, airports, etc.
• The realm of civil engineers
2
8/27/19
Flow Entities
• The ‘Units’
– Planes, trains and automobiles
– Boats
– Pedestrians
– Bikes
• The realm of mechanical engineers
• Order of precedence
– Water, rail, ped, auto
Control Systems
•
•
•
•
•
Air Traffic Control
Traffic Signals
Signs and Stripes
ITS
‘Operators’
– Gas Pedal, Brake Pedal
Human Factors
•
Human Factors
• The Equations of Motion do NOT take into
account driver performance!
• Total Stopping Distance includes:
– Braking Distance (equations of motion)
• What happens the moment are brakes are applied
+
– Perception-Reaction Time
3
8/27/19
Perception-Reaction Time
• The time it takes for our brain to process
information
– To recognize the need to stop
– To tell our foot to apply pressure to the brake
– IT CAN BE MORE TIME, A GREATER DISTANCE
TRAVELED, THAN THE ACTUAL BRAKING
DISTANCE.
– Design is based on total Stopping Distance
• Including PRT!
Perception-Reaction Time
• Essentially response
time to anticipated
braking
• Effected by
–
–
–
–
–
–
–
–
–
–
Driver capability
Driver education
Driver attentiveness
Age
Medical condition
Alcohol/drug use
Fatigue
Sleep deprivation
Emotional state
etc……..
Perception-Reaction Time
• Also effected by
– Roadway stimulus
– Amount of information to be processed
– Complexity of the decision making
•
•
•
•
Standard control devices (MUTCD)
Rules of the road
Roadside ‘clutter’
Driveway and intersection spacing
4
8/27/19
Perception-Reaction Time
• Johannson & Rumar, 1971
– Measured response times
• Design Value
– 85th percentile driver
• One, unexpected, information content (bit)
2.5 seconds
Transportation Demand
• Transportation Systems are derived
– Fulfill a need
– Do not exist for their own purpose
– Indirect
– There must be a demand
5
8/27/19
Level of Service
• Valuation vs. Quantification
– Value is based on one’s belief
• Subjective
– Quantification is objective
• Transportation systems are evaluated based on
impacts or consequences
Modes
• Passenger & Frieght
• Modes
– Land (Highway, rail)
– Air
– Water
– Pipelines
• Intermodal
– Container freight : Ship/Rail/Truck
Public vs. Private
• For Hire or Not For Hire
• Contract or Common Carriers
– Contract: Negotiated contract
– Common Carrier: Scheduled service, fixed routes,
posted fares.
6
8/27/19
I’m From the Government
• …and I’m here to help…
Government Involvement
• Promotes, Regulates and Invests
• Promote
– Mass Transit
– Car Pooling
– CAFÉ
Government Involvement
• Regulate
– Speed Limits
– Truck Restrictions
– Operator Licensing
– NEPA
7
8/27/19
Government Involvement
• Invest
– Interstate Highway Act of 1956
• Eisenhowser, 41,000 Miles, 25 Billion, initially
• Conceived partially for military purposes
– Gas Tax
• State and Federal
– Tire Tax
– Airline Ticket Tax
– National Railroad Passenger Corp. (Amtrak)
Private Investment
• The way it originally was
– Turnpikes
– Railroads
Turnpike
8
8/27/19
Private Investment
• Now
– Railroads; almost 100% private, still
– Airports; Public Capital/Recoup costs
– Highways; almost 100% public, now
– Ports; almost 100% public
• PPPs
Analysis & Prediction
• Done with ‘Models’
– Travel Demand Models
– Traffic Growth Models
– Trip Generation
– Trip Distribution and Assignment
– Capacity Models
– Simulation Models
– Human Behavior & Human Factor Models
9
1/14/2020
The fundamental principles of
HIGHWAY DESIGN & TRAFFIC
ENGINEERING
1
HIGHWAY DESIGN
Founded within the ‘Laws’ of Physics
Thank
you Sir Isaac Newton
F=mxa
2
From Newton…
…we get the
Conservation of
Momentum
P=m1v1+m2v2
HIGHWAY DESIGN
3
1
1/14/2020
HIGHWAY DESIGN
…and from
Conservation of
Momentum, we get the
Kinematic Equations
The basis for accident
reconstruction
4
HIGHWAY DESIGN
…and from the Kinematics, we get the basic
highway design equation
d = V2 / 30 x f
5
HIGHWAY DESIGN
…and where does the expert find this
equation?
In the first of our three ‘bibles’
The ‘Green’ Book
6
2
1/14/2020
THE GREEN BOOK
Officially titled: A Policy on Geometric Design of
Highways and Streets
Published By: American Association of State
Highway and Transportation Officials…AASHTO
7
THE GREEN BOOK
In continuous publication in one form or another since 1954.
…1st ‘super’ highway, the PA Turnpike, opened in…1940
A Policy on the Geometric Design of Rural Highways, 1954 &
1965
A Policy on Arterial Highways in Urban Areas, 1957
A Policy on Design of Urban Highways and Arterial Streets,
1973
Geometric Design Standards for Highways and Other Freeways,
1969
A policy on Design Standards – Interstate System, 1956, 1967
and 1991…all leading to…
8
THE GREEN BOOK
… A Policy on Geometric Design of Highways
and Streets, 1984, 1990, 1994, 2001, 2004
and 2011.
Now in its 6th Edition
The quintessential, peer reviewed, experience
based, Standard of the Industry
The basis for every state DOT highway design
manual
9
3
1/14/2020
THE GREEN BOOK
Geometry.
Width,
Grade, Cross Slope, Curvature, Intersection
spacing, etc., etc., etc.
Two major contexts
Urban
Rural
Hierarchy of Movement
Functional
Classification
10
THE GREEN BOOK
11
THE GREEN BOOK
Freeways
Arterials
Principal
Minor
Collectors
Principal
Minor
Local Roads
12
4
1/14/2020
THE GREEN BOOK
All based on…
Vehicle
geometric characteristics
performance characteristics
Human factors
Vehicle
Our
ability to perceive and react to driving situations
Components of the Driving Task
Three
Control
Guidance
Navigation
13
THE GREEN BOOK
The Guidance Task
Its
all about our brains ability to process
information
What we call: Reaction Time or Perception-Reaction
Time
1971, Johannson & Rumar, “Drivers Brake Reaction
Time”, Human Factors, Vol. 13, No.1
14
THE GREEN BOOK
15
5
1/14/2020
THE GREEN BOOK
16
NOW WHAT?
17
ORDER OUT OF CHAOS
Just add a few
Signs
Some
And
paint
a few colored lights
…the
MUTCD
18
6
1/14/2020
MUTCD
Officially…
The
Manual on Uniform Traffic Control Devices
number 2
‘Bible’
Published
by the US DOT, Federal Highway Administration
(FHWA)
19
MUTCD
20
MUTCD
21
7
1/14/2020
MUTCD
Under who’s authority…
Standard:
The U.S. Secretary of Transportation, under authority
granted by the Highway Safety Act of 1966, decreed
that traffic control devices on all streets and highways
open to public travel in accordance with 23 U.S.C.
109(d) and 402(a) in each State shall be in substantial
conformance with the Standards issued
or endorsed by the FHWA.
22
MUTCD
The Standard of the Industry…
The Manual on Uniform Traffic Control Devices (MUTCD) is
incorporated by reference in 23 Code of Federal
regulations (CFR), Part 655, Subpart F and shall be
recognized as the national standard for all traffic control
devices installed on any street, highway, bikeway, or
private road open to public travel (see definition in Section
1A.13) in accordance with 23 U.S.C. 109(d) and 402(a).
The policies and procedures of the Federal Highway
Administration (FHWA) to obtain basic uniformity of traffic
control devices shall be as described in 23 CFR 655,
Subpart F.
23
MUTCD
Applicable where…
In accordance with 23 CFR 655.603(a), for the purposes of
applicability of the MUTCD:
A. Toll roads under the jurisdiction of public agencies or authorities or
public-private partnerships shall be considered to be public
B. Private roads open to public travel shall be as defined in Section 1A.13;
and
C. Parking areas, including the driving aisles within those parking areas,
that are either publicly or privately owned shall not be considered to
highways;
be “open to public travel” for purposes of MUTCD applicability.
Really??
24
8
1/14/2020
IN PENNSYLVANIA TOO?
The Department of Transportation (Department) publishes Chapter 212
(relating to official traffic-control devices under the authority of 75
Pa.C.S. §§ 3353, 3354, 6103, 6105, 6121, 6122, 6123 and 6123.1.
The purpose of Chapter 212 is to adopt the National MUTCD, to
establish new regulations regarding additional study requirements,
warrants, principles and guidelines not included in the MUTCD; and
to establish greater uniformity for the design, location and operation
of all official traffic signs, signals, markings and other traffic-control
devices within this Commonwealth.
With the promulgation of Chapter 212, the most recent edition of the
National MUTCD, published by the FHWA, is the standard for traffic
control in this Commonwealth. As provided in 75 Pa.C.S. §§ 6103(c)
and 6121 (relating to promulgation of rules and regulations by
department; and uniform system of traffic-control devices).
25
MUTCD
To be effective, a traffic control device should
meet five basic requirements:
A. Fulfill a need;
B. Command attention;
C. Convey a clear, simple meaning;
D. Command respect from road users; and
E. Give adequate time for proper response.
26
MUTCD
Standard:
The responsibility for the design, placement, operation,
maintenance, and uniformity of traffic control devices shall
rest with the public agency or the official having jurisdiction,
or, in the case of private roads open to public travel, with the
private owner or private official having jurisdiction. 23 CFR
655.603 adopts the MUTCD as the national standard for all
traffic control devices installed on any street, highway,
bikeway, or private road open to public travel (see definition
in Section 1A.13). When a State or other Federal agency
manual or supplement is required, that manual or
supplement shall be in substantial conformance with the
National MUTCD.
27
9
1/14/2020
MUTCD
When the public agency or the official having
jurisdiction over a street or highway or, in the case
of private roads open to public travel, the private
owner or private official having jurisdiction, has
granted proper authority, others such as
contractors and public utility companies shall be
permitted to install temporary traffic control
devices in temporary traffic control zones. Such
traffic control devices shall conform with the
Standards of this Manual.
28
MUTCD
All regulatory traffic control
devices shall be supported
by laws, ordinances, or
regulations.
29
MUTCD
This Manual describes the
application of traffic control
devices, but shall not be a
legal requirement for their
installation.
30
10
1/14/2020
COLORS HAVE MEANING!
Standard: The general meaning of the 13 colors shall be as follows:
A. Black—regulation
B. Blue—road user services guidance, tourist information, & evacuation
route
C. Brown—recreational and cultural interest area guidance
D. Coral—unassigned
E. Fluorescent Pink—incident management
F. Fluorescent Yellow-Green—pedestrian warning, bicycle warning,
playground warning, school bus and school warning
G. Green—indicated movements permitted, direction guidance
H. Light Blue—unassigned
I. Orange—temporary traffic control
J. Purple—lanes restricted to use only by vehicles with registered
electronic toll collection (ETC) accounts
K. Red—stop or prohibition
L. White—regulation
M. Yellow—warning
31
WORDS HAVE MEANING
When used in this Manual, the text headings of Standard, Guidance, Option, and Support shall be
defined as follows:
A. Standard—a statement of required, mandatory, or specifically prohibitive practice regarding a
traffic control device. All Standard statements are labeled, and the text appears in bold type. The
verb “shall” is typically used. The verbs “should” and “may” are not used in Standard statements.
Standard statements are sometimes modified by Options.
B. Guidance—a statement of recommended, but not mandatory, practice in typical situations, with
deviations allowed if engineering judgment or engineering study indicates the deviation to be
appropriate. All Guidance statements are labeled, and the text appears in unbold type. The verb
“should” is typically used. The verbs “shall” and “may” are not used in Guidance statements.
Guidance statements are sometimes modified by Options.
C. Option—a statement of practice that is a permissive condition and carries no requirement or
recommendation. Option statements sometime contain allowable modifications to a Standard or
Guidance statement. All Option statements are labeled, and the text appears in unbold type. The
verb “may” is typically used. The verbs “shall” and “should” are not used in Option statements.
D. Support—an informational statement that does not convey any degree of mandate,
recommendation, authorization, prohibition, or enforceable condition. Support statements are
labeled, and the text appears in unbold type. The verbs “shall,” “should,” and “may” are not used
in Support statements.
32
PRE-2000
Shall
Should
May
Standard
Guidance
Option
Support
Required, mandatory
POST-2000
Recommended, not mandatory
Permitted
Required, mandatory
Recommended, not mandatory
Permitted
None of the above,
commentary
THE OLD WAY VS. THE NEW WAY
33
11
1/14/2020
MUTCD
Signs
Regulatory
Warning
Guide
Markings
Signals
Temporary Traffic Control (Work Zone)
34
TRAFFIC SIGNALS (CHAPTER 4)
Standard:
An engineering study of traffic conditions,
pedestrian characteristics, and physical
characteristics of the location shall be
performed to determine whether installation of
a traffic control signal is justified at a particular
location.
35
TRAFFIC SIGNALS (CHAPTER 4)
Warrant 1, Eight-Hour Vehicular Volume
Warrant 2, Four-Hour Vehicular Volume
Warrant 3, Peak Hour
Warrant 4, Pedestrian Volume
Warrant 5, School Crossing
Warrant 6, Coordinated Signal System
Warrant 7, Crash Experience
Warrant 8, Roadway Network
Warrant 9, Intersection Near a Grade Crossing
36
12
1/14/2020
TRAFFIC SIGNALS (CHAPTER 4)
The satisfaction of a traffic
signal warrant or warrants
shall not in itself require the
installation of a traffic
control signal.
37
TEMPORARY TRAFFIC CONTROL (CHAP. 6)
Standard:
The needs and control of all road users (motorists,
bicyclists, and pedestrians within the highway, or on
private roads open to public travel (see definition in
Section 1A.13), including persons with disabilities in
accordance with the Americans with Disabilities Act of
1990 (ADA), Title II, Paragraph 35.130) through a TTC
zone shall be an essential part of highway construction,
utility work, maintenance operations, and the
management of traffic incidents.
38
YES, PEDESTRIANS TOO!
Standard:
The various TTC provisions for pedestrian and worker safety set forth
in Part 6 shall be applied by knowledgeable (for example, trained
and/or certified) persons after appropriate evaluation and
engineering judgment.
Advance notification of sidewalk closures shall be provided by the
maintaining agency.
If the TTC zone affects the movement of pedestrians, adequate
pedestrian access and walkways shall be provided. If the TTC zone
affects an accessible and detectable pedestrian facility, the
accessibility and detectability shall be maintained along the alternate
pedestrian route.
39
13
1/14/2020
TYPICAL APPLICATIONS
40
TYPICAL APPLICATIONS
41
CAN I BUY THE MUTCD?
Nope!!!
Its FREE
http://mutcd.fhwa.dot.gov/
42
14
1/14/2020
HOW MUCH DO WE NEED?
43
MORE THAN WE CAN AFF0RD, LIKELY!
The third ‘Bible’
The Highway Capacity Manual (HCM)
Published by the Transportation Research
Board of the National Research Council of the
National Academy of Sciences.
Can’t get much more scholarly than that…
44
HCM
Originally published in 1950.
Subsequent editions in 1965, 1985, 1994,
1997, 2000 and 2010.
TRB’s most widely used and referenced
document.
Has companion Highway Capacity Software
(HCS)
Introduces the concept of Level of Service
45
15
1/14/2020
LEVEL OF SERVICE (LOS)
Measure of Quality
Operational conditions in a traffic stream
Parameters (Measures of Effectiveness)
Speed
& Travel Time
to Maneuver
Traffic Interruption
Comfort & Convenience
Freedom
46
LEVEL OF SERVICE (LOS)
Six LOS defined
Different for each class of highway,
intersection, type of facility.
Run from LOS A to LOS F
LOS
LOS
A being the best
F being the worst or ‘failure’
47
LEVEL OF SERVICE (LOS)
Safety is not included in
the measures that
establish level of service.”
“
48
16
1/14/2020
LEVEL OF SERVICE (LOS)
Typical LOS for design of new facilities…
C
Typical minimum allowed operational LOS…
D
49
LEVEL OF SERVICE (LOS)
50
LEVEL OF SERVICE (LOS)
Designed for the ‘Peak Hour’
Can
have a morning and evening peak
as:
Defined
The
four highest, consecutive peak 15 minute periods
51
17
1/14/2020
HCM
The HCM contains the basics for such things
as:
Traffic
signal timing
crossing timing
Green, yellow, red times
Pedestrian
…in
conjunction with ‘local’ (PennDOT) preferences
52
SUMMARIZING
The Green Book establishes the geometry of
the intersection…
The MUTCD establishes the level of traffic
control…
The HCM gives us the tools to make it function.
…if only we knew how to drive, paid attention and
didn’t expect so much from our vehicles…
53
FINAL THOUGHTS
32,367 traffic fatalities in 2011 in the U.S.
(NHTSA data) (88 people/day)
Still one death every 16+ minutes.
31,940 fatalities related to firearms in 2011 in
the U.S. (CDC data)
507 airplane deaths in 2011…worldwide
Lowest
Almost
19,766
in 62 years
4 deaths in the span of this presentation
were suicide
54
18
1/14/2020
QUESTIONS
55
19
Highway Capacity Manual
Flow
• Uninterrupted
• Interrupted
Capacity
The capacity of a facility is the maximum hourly
rate at which persons or vehicles reasonably
can be expected to traverse a point or a
uniform section of a lane or roadway during a
given period under prevailing roadway
roadway, traffic
and control conditions.
Level of Service
Level of service (LOS) is a quality measure
describing operational conditions within a
traffic stream
stream, generally in terms of such
service measures as speed and travel time,
freedom to maneuver,
maneuver traffic interruptions and
comfort and convenience.
Level of Service
• Six LOS defined for each type of facility
–A
–B
–C
–D
–E
–F
• Safety is not included in the measures that
establish LOS
Base Conditions
Uninterrupted
d Flow
l
• 12 foot
oot lanes
a es
• 6 foot clearance from edge road to nearest
obstruction
• Free flow speed of 60 MPH
p
g cars onlyy
• No Trucks,, passenger
• Level terrain
passingg zones on two lane highways
g
y
• No p
• No impediments to through traffic due to traffic
control or turning vehicles
Base Conditions
Intersection Approaches
h
•
•
•
•
•
•
•
12 foot lanes
Level grade
No curb
b parking
ki on approach
h
No trucks, passenger cars only
No busses stopping in travel lane
Intersection not in CBD
No pedestrians
Factors affecting Base Conditions
• Roadway Conditions
• Traffic Conditions
– Vehicle
V hi l TType
– Directional and Lane Distribution
• Multi
M l i llane approaches
h rarely
l achieve
hi
l
lane
b
balance
l
• Control Conditions
• Technology
– ITS
Measures of Effectiveness (MOEs)
Performance measures that can be estimated
quantitatively.
Speed
Delayy
Analyses
1 Operational
1.
– Current or anticipated conditions
2 Design
2.
– Establish the detailed physical features
3. Planning
– Strategic, long term
Volume & Flow Rate
• Volume
– The total number of vehicles that pass over a
given point or section of a lane or roadway during
a given time interval. (Annual, daily, hourly or sub‐
hourly)
• Flow
Fl R
Rate
t
– The equivalent hourly rate at which vehicles pass
over a given point or section of a lane or roadway
during a given time interval of less than 1 hour
(Usually 15 minutes)
Peak Hour Factor (PHF)
• PHF = Hourly Volume/Peak Flow Rate
• For 15 minutes periods:
PHF = V/(4
V/(4xV
V15)
• Also expressed as: The addition of the four
highest, consecutive peak 15 minute periods.
• If you know PHF and volume:
V15 = V/PHF
Free Flow Speed
The average speed of vehicles on a given facility,
facility
measured under low‐volume conditions, when
drivers tend to drive at their desired speed and
are not constrained by control delay.
Interrupted Flow
• Operational State defined by:
– Volume and flow rate
– Saturation flow & departure headways
– Control variables
– Gaps
G
in
i conflicting
fli ti traffic
t ffi streams
t
– Delay
Signal Control
The most significant source of fixed interruptions
on an interrupted‐flow facility is the traffic
signal.
• Example:
– 90s signal
g cycle
y
– 30s green time to approach
– If lanes have a max flow rate of 1500 vph (free
flow condition), over the course of an hour, the
approach can only service 1/3 of the flow rate, or
500 vph.
vph (30s/90s) = 1/3
Saturation Headway
Queuing
• When demand exceeds capacity at an
approach to a signalized intersection at the
start of an effective green period,
period a queue
forms.
• A queue also forms when arrivals wait at a
service area.
Undersaturated
conditions: all
vehicles are
serviced
• S = Mean Service
Rate
• V = Mean Arrival
Rate
• tQ = time duration
of queue
Traffic Variation
Methodologies
• Urban Streets
• Signalized
Intersections
• Un‐signalized
Intersections
•
•
•
•
Pedestrians
Bicycles
Two‐Lane Highways
Multilane Highways
• Freewayy Facilities
• Basic Freeway
Segments
• Freeway Weaving
• Ramps and Ramp
J ti
Junctions
• Interchange Ramp
Terminals
• Transit
Urban Street Concepts
Pedestrian Concepts
Multi‐Lane
Multi
Lane Highway Concepts
Two Lane Highway Concepts
Freeway Concepts
• See Handout
Transit Concepts
Urban Street Methodologies
Travel Speed Defines LOS on Urban Streets
Pedestrian Methodologies
Capacity = 23p/min/ft
Bicycle Methodologies
Two‐Lane
Two
Lane Highway Methods
Multi‐Lane
Multi
Lane Highway Methods
Freeway Methodologies
Basic Freeway Segments
Freeway Weaving
Ramps
Interchanges
Transit Methodologies
2/13/18
At-Grade Intersections
• 90 degree angles
– Safety and economy
• Accommodate vehicles and pedestrians
• Maximize offsets
– Typical minimum spacing 250 feet
• Minimize conflict points
1
2/13/18
2
2/13/18
Roundabouts
Not a traffic circle
Modern Roundabout
• ‘Old’ way
• No Yield sign for
approaching vehicles
• Vehicles in circle yeild
• ‘Through’ movement enters
and crosses at high speed
• Minimal deflection
• Increase diameter and size
to provide weaving areas
• ‘New’ way
• Yield sign for entering
traffic.
• Vehicles in roundabout
keep moving
• Deflection is maximizied
• No weaving/Small diameter
3
1/30/18
Highway Safety
• USDOT
– FHWA
• HPMS
– NHTSA
• FARS
– FMCSA
• SAFER
VMT v FAT
YEAR
VMT (billion)
FAT
2005
2978
43510
2009
2964
41259
2011
2968
32310
Accident v. Crash
1
1/30/18
Causes
•
•
•
•
Human Factors (part of every crash)
Roadway Conditions
Vehicle Conditions
Environmental Conditions
SAFETEA-LU
• 2005
• States Required to develop SHSPs
Highway Safety Manual
• AASHTO, 2010
– Condition diagrams
– Collision diagrams
• Accident clusters
– Tables 5.6 thru 5.13
2
1/30/18
Reduction
• CRF
– Percent reduction in number of crashes due to
countermeasures
• CMF
– 100(1-CRF)
– CMF < 1: will reduce crashes
– CMF >1: will increase crashes (see page 224)
Safe Design
• Table 5-27
• Access Control
– PennDOT 441
• Shoulders
• Lane Width
• Intersection sight distance
– Sight Triangles
• Traffic Calming
• Peds
• Clear Zones
Traffic Calming
• The combination of mainly physical measures
that reduce the negative effects of motor vehicle
use, alter driver behavior, and improve
conditions for non-motorized street users.
• Where?
– Local residential streets
– Collector streets with predominantly residential land
uses
– Arterial roads within downtown districts or
commercial areas (with posted speeds of 40 mph or
less)
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Bulb-Out
Chicane
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Gateway
On-Street Parking
Traffic Circles
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Circle vs. Roundabout
Speed Humps
Not Bumps
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Not Bumps
Raised Intersections
Semi-Diverter
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Diagonal Diverter
RIRO
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Raised Median Thru Interection
Street Closure
Raised Crosswalks
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Traffic Calming
• Legal Issues
– Follow the manual and
procedures
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Traffic Impacts
• Traffic & Land Use = Intrinsically Linked
o Cannot separate
o Cannot change one without
affecting the other
o No need for one without the other
o Co-dependent on each other
• Land Use vs. Mobility: AASHTO
Traffic Impacts
How are the new flow entities going to impact
the fixed facilities and control systems.
And/Or
What changes/improvements to the fixed
facilities and/or control systems are needed to
support the new flow entities.
Traffic Impacts
• Each new development needs a study
>100 new vehicle trips
• 160 new single family houses/220
multifamily units
• 10,000 SF retail/commercial
• 60,000 SF office space
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Traffic Impact Study
Four Basic Questions Answered (Goals)
1.Existing Traffic Conditions
2.Additional traffic from development
3.Impact to existing conditions
4.Necessary roadway improvements
to support new traffic and
ameliorate impacts.
Traffic Impact Study
Questions/Assumptions that need to be answered/
made in order to complete the study successfully
• Size of the study area
o Dependent on type of development, spacing of intersections, etc.
• Peak Period(s)
o Weekday peak
o Midday peak
o Saturday peak
• Time frame
o Base Year
o Horizon Year
Traffic Impact Study
Questions/Assumptions that need to be answered/
made in order to complete the study successfully
• Background Growth
o The normal growth without the proposed development
• Already committed improvements
o Up to the horizon year
• Study Methodology
o Version of HCM/HCS
o Growth %
o Local jurisdiction requirements
• Additional analyses
o Sight distance
o Accidents
o Etc….
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Steps
• Meeting with the municipality
• Data collection
• Analyses
o Trip Generation
o Trip Distribution
o Background growth
o Trip Assignment
o Capacity Analysis
o Proposed Improvements
Trip Generation
• ITE Trip Generation Manual
o New Trips
• Modal Split
o Internal Trips
o Pass-By Trips
Trip Distribution
• Existing traffic patterns
• Various analyses
o How the trips enter and leave the
site
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Background Growth
• Historic data
• Set by jurisdiction
o DVRPC
• Philly Region: 2%
Traffic Assignment
• How the traffic is assigned to the road
network.
o Iterative
o Existing patterns
o FHWA O-D pair calculation
Capacity (Intersection)
Analyses
• Compare LOS
o Existing Conditions
o Proposed conditions (with generated traffic)
• Current Period
o Future Conditions w/o Site Traffic
• Includes background growth
• Multiple Horizons (2 year, 10 year)
o Future Conditions w/Site Traffic
• Multiple Horizons (2 year, 10 year)
• Assess Impacts
o Make recommendations
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Site Conditions
• Roadway characteristics such as functional classification, lane widths, shoulder
widths, truck percentages, curbing, and approach grades
• Prevailing vehicle speeds (a speed study should be completed to determine 85th
percentile speeds)
• Sight lines for signal head visibility and for consideration of turn on red prohibition and
protectedonly left turn phasing
• Adjacent land uses and their traffic generating characteristics (vehicles and
pedestrians)
Chapter 4 - Traffic Signals Page | 4-33
Pennsylvania Department of Transportation
Traffic Engineering Manual (Pub. 46) February 2012
• Presence of sidewalks
• Proximity to private residences
• Proximity to schools and churches
• Turning radii
• Driveways
• Nearest signals
• Presence of utilities
• Railroad grade crossings within 1,000 feet of the intersection
Traffic Data
• Turning movement counts for the AM, Midday, and PM peaks of a
typical weekday (Tuesday through Thursday during a non-holiday week)
or otherwise determined by the municipality and the Department. The
data must be less than three years old at the time of the study
completion.
• Additionally, for purposes of developing timing patterns, the data
must be adjusted to the year in which the traffic signal or improvement is
to become active.
• Turning movement counts for school arrival and dismissal periods if
applicable and for any other special time period that is of concern to
the engineer or to the party initiating the study or otherwise determined
by the municipality and the Department. (e.g. Sunday church dismissal,
movie theater discharge peaks, etc.)
• Pedestrian counts for the same periods
• 24-hour automatic traffic recorder counts if deemed appropriate to
the needs of the study
• Pedestrian need evaluation
• Gap analysis (if applicable)
Crash Analysis
• The last five full years of available crash data,
preferably reportable and non-reportable data
collected from the Department and the local
municipality.
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Speed Terms
1. Average Speed: Arithmetic mean (two
types)
2. Median Speed: 50th percentile speed
3. Modal Speed: Most numerous spot
speed
4. 85th Percentile Speed: Design value
5. Pace: Most numerous range of speeds
6. Standard Deviation
Traffic Stream Variables
• Average or Mean Speed
o Collected or measured speed is an instantaneous speed or a spot speed
• Represents one vehicle
o We want the mean speed of the entire traffic stream
o Two ways:
• Time Mean Speed
• Space Mean Speed
Time Mean Speed (ut)
• Arithmetic Average of
the spot speeds
o N = number of observations
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Space Mean Speed
• Harmonic average speed
o The average travel time it takes N vehicles to travel a length of Roadway
D
Space Mean Speed
• Time (seconds) it takes one vehicle to travel
distance (D) (feet)
• The average travel time for (N) vehicles
Space Mean Speed
• Average speed over the average travel time of the
spot speeds
o Harmonic Average
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Traffic Stream Variables
Time Mean Speed
Space Mean Speed
Volume
1. AADT: average annual daily traffic
2. ADT: average daily traffic
3. PHV: peak hour volume
o 4 Consecutive Peak 15 minute periods
4. Classification
o DD
o % trucks
5. VMT: vehicle miles traveled
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• VMT is calculated by multiplying the amount
of daily traffic on a roadway segment by the
length of the segment, then summing all the
segments’ VMT to give you a total for the
geographical area of concern.
• Texas A&M, TTI
• BTS
• FHWA, Highway Statistics
Index 1995 = 100
115
110
United States
Pennsylvania
105
100
95
1995
1996
1997
1998
1999
2000
How to Count
• Call someone
• Go to DVRPC website
•
•
•
•
•
Pneumatic road tubes
Radar/side of road based systems
Inductive loops
Video processing
Manual Intersection counting
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What to Count
• Cordon Counts (macro)
• Screen Line Counts (micro)
• Roadway counts
oCan also be used for
classification
• Intersection Counts
• Ped Counts
Adjustments
• Factoring
oHourly
oDaily
oMonthly
oSeasonal
oBy Location
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Parking Studies
• On or Off Street
• Space Ho...
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