h2g2 The Hitchhiker's Guide to the Galaxy: Earth Edition

Please note that, in the small towns that surround the Turnpike and Parkway exits, Speed Limit signs are used as fund raising opportunities, and police cars have either (a) perfected the ability to materialize at will (a la the TARDIS) or (b) have found places just off the road behind a billboard or at an intersection where they remain mostly invisible. Favorite places are just where the limit drops from 40 to 25, so they can stop you for "recklessly" traveling at 39 in a 25 zone, taking advantage of the laws of inertia or your lack of focus on the sign (which may be conveniently covered by a tree branch).

This explains the large number of attorneys specializing in assisting drivers with traffic offenses.

Driving experiences shared around the water cooler(or equivalent)are useful to identify locations others have experienced.