Ironically, I was told that one of the most uncorrupt agencies here is not the police, who are corrupt but not too bad (unlike the ones in Rio who are pretty badly corrupt), but the traffic bureau who have a type of traffic cop who can issue tickets, etc. They are everywhere, making sure nothing happens to disrupt traffic. Traffic is such a politically radioactive topic here, no politician can afford to have a corrupt and inefficient traffic bureau. Again, its all about the incentives. And they are efficient: an illegally parked car was causing a bit of a jam yesterday and so I saw the traffic bureau swoop in with a flatbed tow truck and remove it in seconds flat (with alarm screaming) they left a big sign on the curb that said "ILLEGALLY PARKED CAR HAS BEEN REMOVED." No ticket, no warning - boom - car gone.
Note to self: never rent a car in São Paulo.