As red-light cameras have proliferated over two decades to hundreds of cities and towns, there is one troubling detail: They don’t always make traffic intersections safer, says Wall Street Journal “Numbers Guy” columnist Carl Bialik. Police departments in 500 cities and towns use the cameras—and, usually, signs warning of their presence—to record motorists who run red lights and to ticket them. The goals are to deter drivers from going through an intersection after the light has turned red and to prevent dangerous crashes.
Places like Los Angeles, Philadelphia, and St. Petersburg., Fl., found that crashes increased where cameras were installed. Counting rear-end crashes can sometimes mean the cameras increase the accident total, as drivers slam on the brakes when they see a warning. An overall increase in collisions can be worthwhile, some researchers say, if the most severe crashes decline. Red-light cameras have been controversial. Privacy advocates regard them as intrusive, and many motorists complain they have been unfairly ticketed for relatively minor infractions, such as rolling right turns on red. The conflicting research results on cameras’ effectiveness have made them a contentious issue for local authorities.