The Tennessee state House of Representatives will consider enacting legislation as early as today to ban the practice of shortening the duration of yellow lights where red light cameras are installed. The measure, introduced in the form of an amendment by retiring Representative Phillip Pinion (D-Union City), has already passed the state Senate.

"No state agency or any political subdivision of the state that installs, owns, operates, or maintains a traffic-control signal light in an intersection that employs a surveillance camera for the enforcement or monitoring of traffic violations shall reduce the time exposure of the yellow light at such intersection with the intended purpose of increasing the number of traffic violations," House Bill 3854 states.

The bill coincides with an expected vote on legislation that, although promoted as a limitation on their use, gives the green light to cities throughout the state to install automated ticketing machines (view bill). The net effect of the yellow light limitation would be negligible, however. There are only a handful of documented cases of cities shortening yellow light duration after the installation of red light cameras.

The more significant problem, as documented in a report by the office of the US House Majority Leader in 2001, is that cities following national signal timing guidelines have systematically given motorists less warning of impending red lights (view report). Cities and traffic camera vendors have been found that intersections with the shortest yellow lights are the most profitable locations for cameras -- but the signals in many cases have been short for ten years or more (see San Diego memo). In 2005, the Texas Transportation Institute reported that cities interested in reducing accidents could increase yellow signal timing by one second above the recommended ITE minimum value (view report).

A full copy of the legislation is available in a 45k PDF file at the source link below.