Cop cams, safety or revenue?

From McClatchy (again via Boing Boing) Cop cameras don't just catch speeders, they raise cash

There should be an equilibrium between level of enforcement (both frequency/coverage of enforcement and the associated fines) and maximum revenue, just as between level of enforcement and maximum safety. These two equilibria however are likely not equal. Formulating this model would make a good Ph.D. written exam question.