Traffic cameras have always been good fodder for debate in the District, whether that’s between members of the Council, regarding former mayor Adrian Fenty’s plans to install them on the back of street sweepers, or concerning allegations that they are more prominent in neighborhoods with a high population of African Americans. But according to a recent study by the Insurance Institute for Highway Safety, they work: the IIHS found that after installing red light cameras, the District’s fatal crash rates at intersections with the devices dropped by 26 percent.