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Stop or Speed Through a Yellow Light

Engineering graduate student Zhixia Li was attracted to UC because of the real-world education and experience the university provides.

In return, he’s headed a real-world project that every driver can relate to. It’s a project on which he has presented and published nationally and which has appeared in international news media, including The Washington Post, The Boston Globe and many others.

Li’s research looks at what he calls the “yellow light dilemma.” Are you, as a driver, more likely to stop or to speed through a yellow light?

Here’s what he found when conducting research, in cooperation with the Ohio Department of Transportation, at intersections in Akron, Cleves, and Fairfield, Ohio: Certain factors make it more likely you’ll opt to speed through an intersection vs. stop at the light. 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 vs. 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. 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 vs. a yellow light set to persist for 4 seconds. Ditto for a yellow light that persists for 4 seconds vs. a yellow light that persists for 3 seconds.

This UC research will help traffic engineers to 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.

In this research, Li has worked with UC’s Heng Wei, assistant professor of civil & environmental engineering.

Related Info:


  • Ashley Kempher, videographer and editor
  • Travis Estell, website editor
  • Kelly Rossberg, narrator

More Information:

M.B. Reilly
Assistant Director, Public Relations
Edwards II, Suite 3300