Talk about a traffic jam!

The Mackinac Bridge Authority voted unanimously Tuesday to close the bridge to all traffic during the annual Labor Day bridge walk in September.

The bridge will be closed from 6:30 a.m. to noon to all traffic, leaving an estimated 4,000 drivers stranded on either side of the bridge on one of the busiest traffic days of the year.

The action was taken at the request of the Michigan State Police and the U.S. Department of Homeland Security, which are responding to threats posed by terrorists using vehicles to plow into crowds to inflict the most possible damage.

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Lt. Brian Budde of the Michigan State Police recalled terrorist attacks in Nice, France; Berlin, Germany; Stockholm, Sweden, and on the campus of Ohio State University as reasons for the precautions. In all of those cases, terrorists used trucks or cars as battering rams through large crowds of people, killing more than 100 people and injuring hundreds more.

“At this time there are no credible threats in Michigan,” he said. “But as the summer months approach, this event and other open air events, is what we’re concerned about.”

Mike Baker, of the U.S. Department of Homeland Security added, “The only other solution is to discontinue the event and we don’t want to do that. Based on what we know now, this would be sufficient to reduce the risk.”

Between 30,000 and 60,000 people participate in the annual 5-mile walk across the Mackinac Bridge that connects the state’s Upper and Lower Peninsula. Typically, the northbound lanes remain open during the bridge walk and an estimated 9,000 vehicles use the bridge during that time, Baker said.

But with enough advance warning of the closure, he said, that number is expected to be cut in half. In addition, buses carrying walkers once they’ve finished the bridge walk and emergency vehicles will be allowed on the bridge during the walk.

Robert Heilman, president of the Mackinaw City Village Council, wondered about the huge traffic jam on either side of the bridge.

“What is going to be done to help these people when they’re struck on the freeway for five and a half hours?” he said.

The state and homeland security department will be putting portajohns on each side of the bridge, setting up water patrols for people who need water or snacks during the delay and getting the word out well in advance of the bridge walk to try and cut down on the number of people stuck, Baker said.

“This is about safety first and the safety decision drives all the other decisions,” said Matt McLogan, a bridge authority member.

Contact Kathleen Gray: 313-223-4430, kgray99@freepress.com or on Twitter @michpoligal