Stop or Speed Through a Yellow Light? That Is the Question

Transportation engineering PhD student Zhixia Li was attracted to the University of Cincinnati because of the real-world education and experience the university provides.

In return, he’s headed two real-world projects that every driver can relate to. One project was funded by the Ohio Transportation Consortium (OTC) to provide a proven approach for looking at what Li calls the "yellow light dilemma." The other is currently funded by the Ohio Department of Transportation (ODOT) to apply the proven approach to investigate intersections in Akron, Cleves and Fairfield, Ohio. Along with his advisor, Associate Professor Heng Wei, the principle investigator of those projects, Li has presented and published the results, nationally and internationally.

Are you, as a driver, more likely to stop or to speed through a yellow light? Here’s what he found when conducting research: Certain factors make it more likely that you’ll opt to speed through an intersection rather than stop at the light.

The results of his research with his advisor, “Analysis of Drivers' Stopping Behaviors Associated with the Yellow Phase Dilemma Zone — An Empirical Study in Fairfield, OH,” will be presented at the 2010 American Society of Highway Engineers National Conference on June 9-13, 2010, in Cincinnati, at the Hilton Cincinnati Netherland Plaza.

So what are the factors that make us run the yellow? These include

• Lane position: Drivers in the right lane are 1.6 times more likely to speed through a yellow light as compared to drivers in the left lane.
• Type of vehicle: Drivers in heavy trucks are more likely to “pass through” a yellow light versus drivers of automobiles, SUVs, vans or pickup trucks.
• Travel speed and speed limit: The greater the traveling speed of a vehicle at the onset of a yellow light, the more likely that vehicle is to pass through a yellow light. Another finding: the higher the posted speed limit, the more likely vehicles are to pass through a yellow light.
• Timing of light: Yellow lights are typically set to persist between 3 to 5 seconds (Ohio law dictates 5 seconds). Drivers coming upon an intersection where the yellow light persists longer are more likely to pass through the yellow light. For each “additional” second a yellow light persists, drivers are more than three times as likely to pass through an intersection. So, for example, a driver is more than three times as likely to pass through a yellow light set to persist for 5 seconds versus a yellow light set to persist for 4 seconds. Ditto for a yellow light that persists for 4 seconds versus a yellow light that persists for 3 seconds.

Li's research has won many awards, including the 2009 Institute of Transportation Engineers (ITE) Daniel B. Fambro Best Student Paper Award (one winner internationally); first place, 2009 ITE Great Lakes District Student Paper Competition (Great Lakes District includes Ohio, Indiana, Michigan, and West Virginia); and the 2009 Ohio Transportation Consortium (OTC) Best Graduate Student Paper Award.

This UC research will help traffic engineers consider and test safety and traffic efficiency measures, including the positioning of sensors that time traffic lights.

And it just might help drivers consider their own actions when in the yellow light dilemma zone.