south north [our xenophobia is showing!] of Fremont, near Newark and Hayward--was recently caught re-timing their traffic signals so that the yellow light is shorter than the legal limit. Why? Well, this makes it easier for motorists to run a red light, then get caught by the red-light cameras, which in turn gets the city more money from increased traffic tickets.
According to Left Lane (via Motorists.org), five other cities were also found guilty of doing the same thing: Dallas and Lubbock, TX, Nashville and Chattanooga, TN, Springfield, MO. One of those cities, it seems, had to "issue refunds by more than $1 million to motorists who were issued tickets for running red lights."
Apparently these are "just instances that have been identified" in yellow-light trickery. More may be more out there.