[fr_freak]

I can tell you from personal experience as a LEO that you can estimate a vehicle's speed within +/- 2 to 3 MPH after a year of traffic duty.

Wrong. You can testify from personal experience that you, yourself, are able to estimate speed within +/- 2 or 3. You really don't have any idea how many of your fellow officers are able to do so with that kind of accuracy. Let's assume that 25% can't - that means incorrect or false speeding tickets 25% of the time. Should we be happy with that?

[TChris]

Let's assume that 25% can't - that means incorrect or false speeding tickets 25% of the time. Should we be happy with that?

If an officer's estimates are that inaccurate, then he will lose cases in court and stop getting any convictions. Those officers soon find it difficult to find work.

If you provide multiple witnesses who testify that the GPS receiver on your dashboard indicated a speed significantly lower than the officer's estimate, or some other strong evidence, then you could beat the officer's testimony.

The point is that a trained officer will likely have a documented accuracy for his estimates. That's going to stand up in court unless you contradict him with something stronger.