Zipper Trucks are amazing machines that quickly pick up and move 1,500 pound blocks of concrete that serve as median barriers on San Francisco's highways:
Each 30-ton, 58-foot 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 ten minutes. When it is completed in the fall of 2013, the $26.5 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.
Watch the above video showing a Zipper Truck cruising down Doyle Drive in dense traffic.
Link -via The Presurfer
the drivers seem more dangerous than the truck, driving in the left lane for no reason
It's also very safe if you think about it. The vehicle is moving with traffic, pulling the barrier to the right. So the lane doesn't exist behind it (no merging or avoiding it required), and it's moving too slowly to over take cars in front of it. Likewise, cars approaching from the other direction can't hit it because its on the opposite side of the barrier, traveling in a lane that doesn't exist for them. The only way you could collide with the vehicle or barrier is to purposefully sideswipe it (or accidentally I suppose if you suddenly lost control of your car).