San Francisco’s iconic Golden Gate Bridge has been shut down for the longest period in the 77 years it has spanned the bay in order to install a safety barrier to increase the safety of vehicle travel.

The bridge was restricted to buses, bikers, and pedestrians as crews worked on the barrier, which are intended to prevent head-on collisions on the bridge. Such collisions have killed 16 people in 128 crashes since 1970, according to an Associated Press report.

Crews laid down the barriers, installed tracks that the barriers could be moved on, and then plugging up the holes left by the plastic rods that formerly divided the two streams of traffic.

The entire barrier was installed by late Saturday, and crews were working on positioning the barriers and doing miscellaneous jobs like painting.

The bridge was closed to vehicles early Saturday, and it is set to reopen early Monday morning — perhaps earlier if crews can get the work done ahead of schedule, according to Priya David Clemens, spokeswoman for the bridge.

Workers used 3,500 concrete blocks clad in steel that were attached together with steel pins along the 1.7-mile stretch of highway along the bridge, as well as the approach portion of Highway 101 north of the bridge.

The barriers is 32 inches tall and one foot wide. It will have to be moved using trucks to accommodate the change in lanes during the rush hour commute.

The Golden Gate Bridge was first opened in 1937, and has been closed before, but for shorter periods than the one this weekend, typically for celebrations or other work projects.

The bridge spans the three-mile-long channel between the San Francisco Bay and the Pacific Ocean, linking San Francisco with the northern tip of of the San Francisco Peninsula. It was declared one of the Wonders of the Modern World by the American Society of Civil Engineers. It is also one of the most photographed structures in the world. Until 1964, it was the longest suspension bridge main span in the world at 4,200 feet, until the Verrazano-Narrows Bridge spanning Staten Island and Brooklyn in New York opened and beat it by 60 feet.