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, and officers have 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 based on money from traffic tickets, and 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.