Speed cameras are the latest way for local governments to earn money. They have been proven to actually increase the amount of accidents (due to sudden jamming on brakes) as well as do not lead to proper law enforcement, since drunk drivers, drug traffickers, etc. are not removed from the roads, as would be done with a police officer issuing a citation in person.
Furthermore, they are frequently set-up and maintained by private corporations (such as Lockheed-Martin in the District of Columbia) which earn a percentage of every ticket they issue, and are therefore an example of law enforcement by private corporations, which is illegal.