SAN FRANCISCO (CBS SF) — Security concerns are going to prompt a major traffic change at this year’s upcoming San Francisco Marathon.

Some drivers who normally go across the golden gate bridge will need to find another route during next month’s race.

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The northbound side will be closed.

Recent terror attacks are prompting this extra measure of security.

The closure of northbound traffic on the bridge is scheduled for Sunday, July 23. There will be no way to cross from San Francisco to Marin County between 6 a.m. and 9 a.m. while the footrace is taking place.

The San Francisco Marathon been going strong for 40 years and, for the past 13, runners have taken over 2 lanes of northbound traffic, leaving one as a buffer, and another for northbound vehicles.

But several recent terror attacks involving drivers plowing into large groups of people have golden gate bridge authorities taking note.

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I think it was time to take pause, revisit the safety and see if we can do this in a safer manner, said Golden Gate Bridge District Capt. Lisa Locati.

She said the change is not just over terror concerns.

You read every day in the paper about distracted drivers and impaired drivers or simply those who have a medical condition that happens when they’re driving, explained Locati.

Golden Gate Transit busses will still be running northbound on July 23rd. Drivers who need to get to marin county from San Francisco will have to head through the East Bay.

The normal number of northbound cars between 6 a.m. and 9 a.m. on a Sunday is about 4,500.

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The Golden Gate Bridge District is planning a huge media blitz so drivers have the chance to make other plans for July 23rd.