Seattle is not yet a sustainable city, not by a long shot. But its transportation policies do serve as useful examples of the main methods now being used to reduce people's automobile dependence, as shown by this fine overview, A Drive Towards Fewer Cars:
In the next 19 years, the city expects 22,000 new housing units and 50,000 new jobs. Assuming the same percentage of people continued driving alone to work, the city estimates it would have to build 20 city blocks of 10-story parking garages downtown.
"Nobody wants to do that," says Patrice Gillespie-Smith, chief of staff of the city's Department of Transportation. "We are very motivated to offer incentives to get people out of their cars."
We cover innovations in personal transportation regularly, but it's important to remember that often the solutions to the problems cars create don't lie under the hood, but in how we build and run our cities.
Be careful that the 20th Century transit system doesn't become obsoleted by 21st Century transit before the loans are paid off. This could happen with a Challenge, as described at http://conversantcars.com. The parking issue is resolved because the new technology (combined with your refusing to increase parking space) makes very small vehicles much more energy efficient than 20th Century transit systems.