Snopes debunks the "E-ZPass used for determining who is speeding" myth.
I've heard this one several times, as far back as a decade ago, but I haven't ever seen someone explain why the police can't use this kind of system to catch speeders. It's nice to see someone presenting the facts, but even this debunking doesn't mention one reason why this would never work. A traffic officer needs to be involved in catching speeders to verify who is driving the vehicle. Otherwise, an owner of a vehicle who happens to have several other family members who drive the vehicle could get a speeding ticket for what another driver did, or even worse you could get ticketed for what your friend does while driving your vehicle.
This may well be an irresolvable problem with trying to use anything like E-ZPass to catch speeders. Even with cameras, you couldn't be sure that it was one rather than another of a set of identical twins or two family members who look similar. They can send you a bill if your vehicle goes through an EZ-Pass lane when it's not supposed to (although the one time I did that I was told I'd get a bill and never did), but they can't touch your driving record without being sure it's you, for the same reason you can't get convicted of a traffic offense if the police officer doesn't show up in court to testify that you're the one they stopped.