How many public officials does it take to change a traffic light?

The answer, apparently, is three.

The city of Charleston is going to try to improve the flow of traffic at the heavily congested intersection of Maybank Highway and River Road on Johns Island just by keeping the light green a little longer. And the plan wouldn’t cost a dime.

Traffic snarls at the intersection every evening as vehicles back up onto the bridge over the Stono River. The problem is so severe that some people call it the “bottleneck bridge.”

Charleston County Councilman Joe Qualey pitched the idea of changing the lights to the city of Charleston, in which the intersection lies. Hernan Pena, the city’s director of traffic and transportation, met with Qualey and Councilman Herb Sass at the intersection Wednesday to talk about the plan. Although Pena agreed to try it, he said he doubts it will work.

Qualey thinks changing the timing of the light so it would allow more traffic from Maybank Highway to pass through the intersection would improve the flow.

If more cars could move through, fewer would back up on the bridge, Qualey said. “There’s nothing to lose,” he said. “If it doesn’t work, we can go back to the old way.”

But he thinks the plan could improve traffic congestion, at least a bit. A similar plan for years has been helping traffic flow more smoothly at the intersection of Folly and Camp roads on James Island on busy beach weekends, Qualey said.

Pena has doubts.

Traffic snarls at the intersection during the afternoon rush hour because the road narrows from two lanes on the bridge to one lane on Maybank Highway, he said. That choke point is a mile from the intersection, so changing the timing of the light probably won’t help. But he’s willing to give it a try by making the green light 10 seconds longer for drivers on Maybank Highway.

And he’s going to be careful not to make the situation at the intersection worse by causing distress for drivers who must wait longer at red lights on River Road to compensate for longer green lights on Maybank Highway.

Now, traffic on River Road must wait 96 seconds at a red light during rush hour, Pena said. Drivers get anxious when they must wait for 120 seconds, but they begin to escalate at about 105 seconds, he said.

When they get anxious, they tend to dart through yellow lights and even run red lights.

If the plan does work, Pena said, he would consider extending the time the light stays green even a little longer than 10 seconds. “But I think it’s unlikely that the change will have an impact in the length of the back-up or the travel time.”

Reach Diane Knich at 937-5491 or on Twitter @dianeknich.