ST. IGNACE, Mich.–Authorities believe approximately 25,000 people took part in the annual Labor Day walk across the Mackinac Bridge during which all traffic was halted for the first time as a security precaution. The Mackinac Bridge Authority says the number of participants Monday was on the lower end. Its website says between 30,000 and 60,000 people typically take part. There were no known threats, But officials cited heightened security awareness about terrorist strikes for banning vehicle traffic on all four lanes this year. There were reports of traffic congestion on roadways leading to the bridge. Pedestrians cross the nearly 5-mile-long span that connects Michigan’s Upper and Lower peninsula. The walk started at around 6:30 a.m. and ended at around noon. The event began in the late 1950s.