I always wondered about this. When times are tough, the officers seem to start getting stricter, writing tickets in cases where they may otherwise give a warning or not bother to pull you over. No, I didn't just get pulled over, but I have been seeing more cars pulled over on my commutes to/from work each day.
The police departments will of course say that they apply the law equally, and it doesn't matter whether the Dow's at 13k or 6k, a person going 90 on the freeway will get pulled over. The conspiracy theorists will say that traffic officers are a huge moneymaker for cities/states, especially when other revenue sources like sales, property and income taxes are reduced in economic recessions, and officers are given a monthly quota of tickets they must write; either a particular number of tickets, or an explicit dollar value.
You can't deny that traffic tickets are a big source of revenue. The question is, do cities write budgets that depend on a certain amount of money from traffic tickets, and then put pressure on the police to meet that intake? And, does that result in police officers having to write $X worth of tickets per month or face disciplinary action?
Obviously the question is jurisdiction-dependent; one city might have a quota policy while others don't. So, I'll consider any answer that can explain and back up a pattern, or that can show that particular jurisdictions do or don't have quotas.