This NY Times article reports on more research that goes into the “who needs a research project to prove that?” category:

. . . the broader question ó whether police officers in some towns are motivated by fund-raising as well as safety when writing traffic tickets ó has been examined systematically by others. Michael D. Makowsky, a doctoral student in economics, and Thomas Stratmann, an economics professor, both at George Mason University, studied the issue in a recent paper, ìPolitical Economy at Any Speed: What Determines Traffic Citations?î
They examined every warning and citation written by police officers in all of Massachusetts, excluding Boston, during a two-month period in 2001 ó over 60,000 in all. Their conclusion wasnít shocking to an economist: money matters, even in traffic violations. They found a statistical link between a townís finances and the likelihood that its police officers would issue a speeding ticket. The details are a little sticky, but they show that tickets were issued more often in places that were short on cash, and that out-of-towners received tickets more often than drivers with local addresses.