I live in Virginia, which is a wonderful state in almost every way, except for the fact that radar detectors are illegal. So, is it possible to create a production car that features enough stealth characteristics to measurably reduce the effectiveness of a radar gun?
The primary ways that aircraft achieve stealth are low observable features and active emitters. Because the jamming of radio signals is very illegal, we would have to focus on the former category. The two primary means for minimizing the aircraft's Radar Cross Section (RCS) revolve around the idea of deflecting the radio waves away from the source through the shape of the vehicle and absorbing the radio energy through specialized coatings. Specialized coatings are sensitive and very expensive, so their use in the automotive environment may not work as well, but if people look into it enough, it could work, especially since these coatings have been around since the Blackbird and the general theory behind them is well known. For example, the F-16 uses an iridium-tin oxide layer that's applied to the canopy that reduces the RCS by 15%.
That leads us to shape, which could probably be fairly easy to implement. The ungainly F-117 (which first flew in 1981) was full of angles designed to deflect radar returns away from the aircraft. Modern computers have allowed for a much sleeker design in stealth aircraft, with the F-22 and F-35 implementing these features while still maintaining visual grace.
Furthermore, it seems to me that most encounters with radar guns occur as I am approaching the officer, so I believe it's realistic to assume that in order to be effective in both cost and execution, the designer of the car would only need to focus on the front of the vehicle. This could prevent a solid speed reading while you react by hitting the brakes as you normally would, and by the time your car reveals a less stealthy Radar Cross Section, you could be travelling in the speed limit.
A great looking car could probably be made with radar reflective features and a reasonable amount of radar absorbing material (RAM) within the hypercar spectrum. The Veneno and Reventon are both examples of cars that are "inspired" by stealth fighters, but I bet with a little more engineering emphasis on actual stealth, you could get real results. I bet you could create a good looking Corvette-level sports car without any RAM and still have enough features to be measurable.
I don't know if any OEM has actually put any effort into creating a stealth car, but I don't think it would be as hard as it looks. It doesn't have to be completely invisible, but if you make it harder to get a solid radar reading, you may be able to get a few extra precious seconds to react.
Photos: Jalopnik, Wikipedia, Autoguide