Analyzing prior research, University of Tennessee researchers drew several conclusions about shortening yellow lights at intersections.
Researchers at the University of Tennessee have drawn several conclusions about traffic signal length and how it relates to red light cameras, in a new study published by Transport Journal.
According to a report on Phys.org, a Web-based science, research and technology news service, professors Lee Han, Chris Cherry, and Qiang Yang in the university’s Civil and Environmental Engineering Department found that shortening a yellow light, lengthening the period when all lights are red, shortening the traffic cycle length and increasing the speed limit in an intersection all increased the chance of drivers running red lights.
Municipalities with red light cameras often pay for them by splitting the revenue from citations issued through the technology or through a monthly fee. That can pose ethical questions for traffic engineers who are responsible for adjusting the traffic signals.
Red light cameras have been a hot issue for the public and governments since they were first introduced. Some have objected due to privacy concerns, while others have contended they serve merely as a government fundraiser.
Each city adjusts traffic signal timing based on a number of factors, but according to Saeed Nowkhasteh, signal operations supervisor for the Seattle Department of Transportation, shortening the yellow is not an option in many cases because cities must adhere to standards put in place by the Institute of Traffic Engineers (ITE).
Some cities look for ways to adjust the traffic lights to increase revenue from red light tickets. But there are limited parameters within which traffic engineers can work. One of the changes they can make is to increase the all-red time. Nowkhasteh said that in Seattle, the all-red time depends on the geometry and size of an intersection. The city is permitted to make the all-red time zero, but they often make that time one second.
When it comes to increasing all-red time, however, Nowkhasteh added that there are two schools of thought. Some believe it makes intersections safer by creating a longer buffer between cross-traffic, but in intersections that don’t have red light cameras, it can increase drivers running red lights once they realize that the long all-red allows them extra time to get across the intersection.
Another finding made by University of Tennessee researchers was that manipulating traffic lights to increase volume to an intersection led to more traffic congestion, but did not affect the chances of drivers running red lights or crashing.
"One of the major challenges with implementing red light camera policy is the conflict of matching incentives of tangible revenue for industry and the municipality contrasted with external cost savings such as safety and congestion, the value of which is not easily captured," Cherry said to Phys.org. "We hope the public sector and the public use our research to reflect on the motivations for changing signal operations."