The Insurance Institute for Highway Safety (IIHS) on Thursday released a brief analysis of red light running incidents in Arlington, Virginia claiming a benefit to the use of photo enforcement. The primary assertion is that violations taking place 1.5 seconds after the light turned red decreased dramatically at red light camera intersections.

"This study provides fresh evidence that automated enforcement can get drivers to modify their behavior," Anne McCartt, senior vice president for research at IIHS, said in a statement.

The IIHS examined four camera intersections in Arlington, four camera-free "spillover" locations in Arlington and four camera-free control locations in Fairfax County. Each location was videotaped from 7am to 7pm on two weekdays for a total of 22 hours during the period in which the cameras were installed but only warning tickets were issued. Another 22 hours of taping took place thirty days later during active ticketing and again one year. Only straight-through and left-hand turn violations were counted. Rolling right turns were excluded, except at one location where all right turns on red are prohibited.

In the after period, the control intersection and the camera intersections proved to have the same number of the most dangerous red light violations (those taking place more than 1.5 seconds after the light turned red). In Arlington's camera intersections and Fairfax County's camera-free control locations, between 1.5 and 1.6 violations were observed for each 10,000 vehicles passing through the intersection. A 2004 Texas Transportation Institute (TTI) study showed that right angle accidents -- the type caused by straight-through violations of red signals at intersections -- do not happen until an average of nine seconds after the signal had changed from yellow to red (view study).

"With one exception, all of the right-angle crashes occurred after five seconds or more of red," the TTI study explained. "Closer inspection of the one exception revealed that it occurred very late at night with both vehicles violating their respective red indications at about the same time."

The IIHS data suggest red light camera violations generate the most revenue for inadvertent violations that take place when conflicting traffic is held by an all-red period. With the cameras operational, 90 percent of all violations occurred in the first 1.4 seconds that the camera was active and accidents do not happen. A total of 61 percent of the violations represented even more minor, split-second violations between 0.5 and 0.9 seconds after the light turned red. Virginia law prohibits ticketing less than half-a-second after the light turns red.

IIHS insists cameras create a "spillover" effect, which means the good habits drivers learn at photo enforced intersections carry over to other locations. This does not appear to have happened in Arlington, as the "spillover" locations saw dangerous red light entries increase 30 percent from 4.7 per 10,000 during the warning period to 6.1 a year later. Non-corridor spillover locations saw a 343 percent jump, and Fairfax County intersections increased 283 percent.

IIHS is funded by major insurance companies that earn additional revenue from photo ticket recipients in Arizona, California and a handful of other states where such tickets carry license points. A copy of the report is available in a 250k PDF file at the source link below.