For years, San Francisco's iconic Golden Gate Bridge was a deathtrap. Cars would zip past one another at 100km/h, separated by a thin line of yellow traffic cones, and head-on collisions were routine. However, a new barrier system -- laid by a massive vehicle known as a Zipper Truck -- will keep passing drivers from landing in each other's laps.
The current traffic separators on the GG Bridge are a series of 48cm tall yellow rubber tubes, hand-placed by Caltrans workers every 8m along the span. Now, as anyone that has plowed through a traffic cone can tell you, they don't do much to impede any vehicle bigger than a moped. That's why, following a rash of head-on crashes in 1996, the Golden Gate Bridge Authority began designing a Jersey Barrier system to protect the opposite-bound lanes of Highway 1.
The barrier blocks themselves measure 82cm tall, 30cm wide, weigh close to 680kg apiece, and connect to form an uninterrupted 4066m long concrete barrier. Depending on traffic conditions -- southbound lanes are clogged for the morning commute, northbound lanes in the evening -- Caltrans will rely on a tool known as a Zipper Truck to pick up and move the barrier between lanes, easing congestion. This process is actually easier said than done.
Each 27-tonne, 18m Zipper Truck is driven by a two-person team. As it passes over the barrier system, a series of wheels gently lifts each block off the street, funnels it through an S-shaped curve under the vehicle, and deposits the block into the other lane. The entire bridge-rearranging process should take less than 10 minutes. When it is completed in the late 2013, the $US26.5 million project will integrate with the zipper system already installed along the new Doyle Drive, to create a seamless, safe approach to the Golden Gate.
"The movable barrier will completely eliminate the crossover head-on accidents," Mary Currie, public spokeswoman for the Golden Gate Bridge Authority, told Gizmodo. "Not all of the fatalities that have happened on the bridge have been [head-on's], but a majority of them have."