Speed Bumps That Flatten for Slow Speeds

Much simpler just to use heavy duty rubber (or similar) and fill it with a non-Newtonian fluid. Think cornstarch and water, or oobleck.

http://www.google.com/search?q=oobleck

http://www.youtube.com/watch?v=yHlAcASsf6U

http://www.youtube.com/watch?v=fYj6Ju8IcW0