A study conducted by researchers at the University of Maryland concluded that the use of red light cameras resulted in a "loss of capacity" at intersections which negatively affects traffic flow.
The researchers noted that other studies involving red light cameras have typically failed to investigate the possibility of any negative side effects due to the use of automated enforcement at intersections. The study by Weldegiorgis, Mishra, and Jha stated:
"Depending on the time the driver arrives at the intersection and other unexpected conditions present at that time s/he can either stop if there is sufficient stopping distance or clear the intersection if there is enough clearing time before the signal turns red. Thus, the driver’s decision at RLC intersections during the yellow interval can be seen as a binary process in which the two main decisions are either to come to a stop or cross the intersection.The study investigated traffic performance at ten locations in Baltimore City and Baltimore County where red light cameras had been used at one intersection but not at another. The researchers concluded that the use of Red Light Cameras resulted in a reduction of intersection capacity of 90 vehicles per hour. "Given the continuous monitoring of intersections by red light cameras, the cumulative impact of capacity reduction may be huge," the report stated. "The capacity loss at red light camera intersections can be considered significant given the fact that the number of red light cameras used to monitor for red light running behavior are increasing nationwide."
Each of the two decisions have their own consequences, which can impact the traffic operation at the intersection. The stopping decision may result in a rear-end collision and the crossing decision may result in a side collision. Moreover, the travel behavior at non RLC (NRLC) and RLC intersections may not be the same for all drivers. One scenario is that fearing RLR violation ticket, some drivers who are aware of the presence of RLCs may decide to stop during yellow regardless of the availability of safe clearing distance before the onset of the red signal. The cumulative impact of such stopping may result in significant delay in a congested transportation network, especially during rush hours. Such stopping may also impede the smooth progression of traffic along arterial roads during rush hours."
Additional Information at TheNewspaper.com