It's a bit more subtle than that: they tend to decrease the incidence of side impact collisions (which have a high injury potential), and increase the incidence

It's a bit more subtle than that: they tend to decrease the incidence of side impact collisions (which have a high injury potential), and increase the incidence of rear impact collisions (which have a somewhat lower, but non-zero injury potential). Overall results vary depending on your definition of success (less total collisions? less injuries? less side impact collisions?) and the characteristics of the intersection (approach speed, sight lines, etc). CDC has a good concise overview: http://www.cdc.gov/motorvehiclesafety/calculator/factsheet/redlight.html http://www.cdc.gov/motorvehiclesafety/calculator/factsheet/r...