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Q. Which light statistically stays on longer, a red light or a green light? It always seems that red lights are always longer, but who knows, since we don’t sit through green ones.

A. Short answer – it varies. The long answer requires an expert like Denys Vielkanowitz, P.E., signal systems management engineer for the city of Wilmington Department of Traffic Engineering.

Vielkanowitz said, “Each traffic signal is timed independently, to efficiently service the approaching or expected vehicular demand.”

“At certain times of the day, traffic signals cycle around freely as traffic arrives, simply called Free Operation,” said Vielkanowitz. “At other times of the day, they are programmed to cooperate with the adjacent traffic signals, called Coordinated Operation. The intention of Coordinated Operation is to program adjacent traffic signals to move of groups or platoons of vehicles through multiple traffic signals before stopping again. This Coordinated Operation includes changing through different timing plans throughout the day to give preference to the predominant movement or established traffic patterns that exist during the different hours of the day.”

He continued, “Each timing plan consists of a cycle length (the time to serve all directions) and split durations (the time for each movement). So as the timing plans change throughout the day due to changing traffic volumes or patterns, so does the cycle length and split values. The intent is to match the timing plans to the volume and directions of the vehicles using the roadways.”

As an example, Vielkanowitz cited Carolina Beach Road. “In the mornings, the predominant traffic pattern is northbound (toward downtown); while in the evenings, it is southbound,” he explained. “All of the traffic signals from the intersection with Front Street/Burnett Boulevard to Antoinette Drive are programmed to move as many vehicles in the predominant direction during those times of the day. Although, at the other times of the day, there is not a well-defined pattern, so they are programmed for general progression in both directions, without giving preference to any one direction. Overnight these signals are in Free Operation, so they cycle around as needed.”

Vielkanowitz said when looking at specific roadways, it’s relatively easy to determine what needs to be done. However, the challenge occurs when two major roadways intersect. He said, “In order to keep one road moving, the other one has to stop. It’s like a big jigsaw puzzle, but the pieces keep changing throughout the day.”

RELATED LINKS:

What is the longest red light in Wilmington? How many stop lights are in service in the city?

Why don’t downtown traffic lights flash red on cross streets and orange on main roads after 8?

Date posted: February 5, 2013

User-contributed question by:
Mick Freed