Actually you are not correct in the many part.
No it is not many.....in the lower 48 US states,
it is two...
just two.
Virginia and DC, thats it......
source:
http://www.radarbusters.com/legalissuesarticle.cfm
I have a radar detector cause I know of some local communities have speed traps and WILL ticket you for just 1 mph over the limit if they feel like it. I have never known any car to have an accurate speedo.
I dont advocate reckless speed or street racing, most I have ever gone was maybe 15 over and that was on a 3 lane highway, that had little traffic and conditions of the weather and pavement allowed for that. I also have had high performance driving schools so I am quite capable of handling the car at those speeds.