Just read an interesting statistical analysis about speeding tickets by Professors Michael Makowsky and Thomas Stratmann. They both appear to be economics professors at George Mason University.
They analyzed a database of Massachusetts speeding tickets. Police there can choose to issue a fine or just a warning on the ticket. They found that police are more likely to fine out-of-town drivers and even more likely to fine out-of-state drivers. It's an interesting discussion, if you can wade through the statistical mumbo jumbo.
The paper is available online at: http://ssrn.com/abstract=961967.