This report tracks the impact of red light monitoring cameras on the frequency of traffic accidents in Houston, Texas. We use data collected over seven years to simulate the effects of camera installation and to estimate their impact. The results show that cameras are associated with a long-lasting reduction in the number of collisions at Houston intersections that averages almost 30 percent for single cameras. We find that intersections with one camera benefit from reduced collisions only on the approach with the camera, whereas intersections with two or more cameras see reduced collisions from all approaches. From September 2006 to December 2009, we estimate that camera-controlled intersections in Houston prevented about 792 collisions in total.