Let customers know what your alcohol policies are by posting them in public view. Place posters in various places around your bar and make your alcohol policies clear to your customers.
If customers know what your policies are, they won't be surprised when you enforce them.
Offer Safe Transportation
Make a standing arrangement with a local taxi service. Call cabs for customers and make it known that safe transportation can be arranged for those who can't drive home. Give customers free overnight parking in your lot so they don't feel obligated to drive home in order to keep their car from being towed.
It isn't wise for employees to drive intoxicated customers home or for you to organize your own taxi service, so just stick to working with another company to get customers home safely.