After a marathon weekend installation, the Golden Gate Bridge has finally gotten the $US30 million movable median barrier system that it so desperately needs. These are the oversized mechanical zipper pulls that will be in charge of changing lanes (quite literally) twice a day to keep traffic flowing smoothly.
The Golden Gate Bridge employs six traffic lanes along its single deck with the center-most lane dedicated to separating the flows of traffic. Its lane configuration can be adjusted to accommodate traffic conditions -- they will roll out four Southbound lanes (into the city) during the morning commute and reverse that in the afternoon, but leave three lanes apiece during the weekend -- but they're really only separated by a series of plastic pylons. So even though they're limited to 72km/h, the chances of a driver accidentally crossing into oncoming lanes is quite high and happens with tragic regularity. 36 people in total have died on the GGB since 1971, 16 of which lost their lives in head-on collisions.
It will take a Sherman tank to break through the new Moveable Median Barrier system from Barrier Systems, however. The system consists of more than 3200, 12-inch wide by 32-inch high units linked together to form a semi-rigid barrier. Each steel-wrapped, concrete-filled unit weighs 680kg.
It takes a 27-tonne, 18m long hulk of a truck to shift the new barrier back and forth among the lanes. Caltrans has two such vehicles dedicated to working on the GGB, and it's a good thing too because each Zipper Truck as they're known (technically they're "barrier transfer machines"), has a top speed of 16km/h and gets just 8km to the gallon.
Each truck is equipped with an S-shaped channel running the length of its undercarriage. As the truck moves past/over a barrier unit, the segment is lifted up and shoved over to the other side of the lane before being set back down as it exits the rear of the vehicle.
This is far from the first such movable barrier system. Similar systems have been installed throughout North America, from Hawaii to Boston. In fact, the system is already in use along Presidio Boulevard (as you can see above), the main thoroughfare leading up to the GGB's southern entrance. [SF Examiner - GGB 1, 2 - Wiki - Barrier Systems Inc]