1. Throw everything out of the window that can lighten the vehicle. Oops, that's if you want the car to fly.
2. Have a passenger carefully crawl out onto the hood and pull off the spark plug wires. This will shut the engine down.
3. Lean out of the window as far as possible and carefully (remember you're speeding) shoot out all four tires with your handgun. The car will be hard to steer after this so aim for something solid like a power pole or Oprah.
4. If you have enough gas, attempt to steer the speeding car onto the nearest race track for a good time trial. It will eventually run out of fuel after maybe 100 laps.
5. With your free hand, quickly dial the next city airport rescue squad on your cell phone. Have them stretch a giant nylon net used for stopping runaway 747's across the freeway for you to zoom into in a really cool way.