Are you sure that there isn't an implied consent when on public roads? For example, at least in the states I've lived, a breathalyzer is sort of mandatory. Of course you don't _have_ to take it based on the 5th amendment, but the penalties for refusing are exactly the same as a DWI.

What I'd like to see some case law on is the _avoidance_ of a roadblock. If you are driving down a road, and you see a roadblock, then perform a legal U-turn, is that probable cause?

I will possibly find out tonight. IANAL, but we're having some friends over this weekend, one of whom is a very liberal defense lawyer who handles lots of cases involving questions like this. Quick example: there was a nazi march in oregon, and a big protest march against it. A cop arrested one guy and searched (with no warrant) his backpack, which contained shoes, bread, and peanut butter. The cop's "cause" was that the backpack looked "suspicious." The jury didn't buy it.

I'll post something about this later.