The Physics of the Yellow Traffic Signal – ITE’s First Recommended Practice

When:  Sep 23, 2020 from 2:00 PM to 3:00 PM (ET)

On March 2, 2020, the Institute of Transportation Engineers (ITE) published its first recommended practice for calculating the duration of the yellow traffic signal. Though ITE has published yellow change interval practices since 1965 and Departments of Transportation have adopted those practices, on March 2, ITE admitted that its old practice is wrong and replaced it with a new practice. The old practice forces drivers to run red lights. Unlike the old practice, the new practice has a new math equation which satisfactorily describes both unimpeded turning and thru-movement traffic. The result of the new equation is that turning yellows are several seconds longer than the thru yellows. Though the new practice is better than the old, the new still omits the case of impeded traffic, misapplies the dynamics of uphill movement, and does not quantify tolerances.

This presentation covers the physics of the new practice and its omissions. The presentation also touches on a history of the yellow light--after all, this is the 100th anniversary of the yellow traffic signal. This history starts with William Potts, continues with Robert Herman (the inventor of the ITE old equation), and ends with Mats Järlström (the inventor of the new equation) and believe it or not, your presenter. There is a tale to tell.



Brian Ceccarelli
Brian Ceccarelli is a licensed professional engineer in the State of North Carolina. Mr. Ceccarelli has a degree in physics from the University of Arizona. As principal software engineer for Talus Software PLLC, Mr. Ceccarelli has developed applications for mining, mechanical engineering and space exploration.

Ceccarelli became interested in traffic engineering when the Town of Cary, North Carolina bestowed upon him a red-light camera ticket. Since then, Mr. Ceccarelli has been published in Traffic Technology International and has been an expert panelist in traffic signal timing for the Institute of Transportation Engineers. Mr. Ceccarelli was one of three appellants who successfully convinced ITE to adopt a more comprehensive physics in its yellow light practice. Ceccarelli has presented for NSPE-NC, the North Carolina Society of Engineers, the American Society of Civil Engineers, and for the United Kingdom International Press’s Autonomous Vehicles Symposiums in Europe and America. Ceccarelli is an expert witness in traffic signal timing and red-light cameras in several States.