Let me point a few things out.
If you're sat in traffic cruising above the normal speed, no one will bother you.
If there's a mobile speed trap, your car must be the only car in the frame for it to be a valid piece of evidence, so if you're following someone you're fine.
Secondly, mobile laser traps are a fairly rare occurance on ones travels, I've come across 3 that've had a pop at me in 30,000 miles. I have a laser jammer though (PM me if you want to discuss that one though).
If it's raining then the police won't use laser traps (so no mobile vans), xenon lights also affect them (although I know for a fact it doesn't stop the gun getting a reading, it can be used in court to evade prosecution).
And finally.
If you're going to speed, accept you might get caught. It's your outlook, and if you need a Road Angel to tell you where GATSO cameras are, you shouldn't be on the road imo.
FYI: Laser detectors are worthless. The only way round mobile traps is
a) not speeding
b) jammers