Here are some ideas floating around that I believe have merit for helping to encourage people to drive less.
Pay as you drive auto insurance; This would pro-rate your premiums based on how much you drove in a year. Check out this website and sign the petition if you think it is a good idea.
Some opponents say it is too complicated and requires sophisticated tracking devices in vehicles. Not so! It can be quite simple. When we lived in New Zealand we had to pay road user charges for diesel vehicles based on mileage. It was a simple card that was purchased and displayed in the windscreen and based on odometer readings. Here we could just have the insurance broker check the mileage. This can work!
The other idea is to have a scanguage or similar device installed on all new vehicles and to have some incentive to have people retrofit existing vehicles with one. What this does is to help you monitor your fuel economy and to put an actual fuel cost to every mile or trip that you drive. It would raise people's awareness of the cost of driving and hopefully encourage them to bike, walk, or use public transit!