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On most major highways, there are tracts of road with medians, and other tracts of road without medians. The lack of a median between lanes of oncoming traffic is a serious safety concern, and requires a solution. Enter the Median Barrier.

It is not clear where or when the first concrete median barriers were made and/or used, but they go on record in the mid-1940s as being used on US-99 on the descent from the Tehachapi Mountains in the central valley south of Bakersfield, CA. The reason for the development was, as noted above, to reduce the number of out-of-control trucks penetrating the barrier, and to eliminate the need for costly and dangerous median maintenance in areas with narrow medians (or none). Of course, these issues are still with us today.

There are 5 different types of Median Barriers both in use and in obsoletion. They are:

(I read that there are actually 6 distinct types, but could not find information on the illusive 6th type)

Each barrier fills a particular niche role in highway safety, but there is a strong move for F-Shape Barriers. Each linear foot of concrete median barrier costs two to three times as much as a steel guardrail median barrier, but provides significantly more protection.

The various barriers are used for temporary and permanent applications.

Movable median barrier

Many cities use median barriers to keep traffic flow separated on roads that were not originally designed with a median. Some cities have portions of road where the number of lanes in each direction is modified twice per day to accommodate the rush hours. That can be done by using changeable traffic direction signs over the lanes.

Sometimes there is a median barrier that is physically moved twice a day. That can be helpful during road reconstruction.

Cities around the world have machines that efficiently pick up median barriers and move them one lane over. It's a remarkable invention.

In the US, a typical style of median barrier is called a Jersey barrier. A Jersey barrier is made of concrete, about 3.5 feet (a meter) tall, and about 4 feet long. Median barriers are usually broad at the base, about 2.5 feet wide, and angle sharply inwards from the the base for about a foot. They are made that way in case someone driving a car veers into them. It's safer that way.

A movable median barrier is like a Jersey barrier, but has a top shaped like a "T". Movable barriers are linked, one to another, with steel wire, in order for them to be picked up and moved as a chain. The "T" at the top allows a specially designed truck to lift the barriers, move them sideways through a track on the undercarriage, and set them back down on the ground, one lane over.

"Zipper lane" is a short phrase for a movable median barrier. The trucks that move the barrier are called zipper machines.

Here are some pictures of a Zipper Machine in action.

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