They are also known as K-rails (especially in the western United States or when used temporarily during roadway construction - K-rail is the California Department of Transportation specification for temporary concrete traffic barriers) or traffic dividers.
The Jersey barrier was originally developed at Stevens Institute of Technology in Hoboken, N.J., United States, under the direction of the New Jersey State Highway Department to divide multiple lanes on a highway. A Jersey barrier stands 3 feet tall and is made of poured concrete. Their widespread use on the highway has led to many other uses as a general barrier (for instance, during general construction projects or constructing temporary walkways).
The design of the Jersey barrier was specifically intended to minimize damage and reduce the likelihood of a car crossing into oncoming lanes in the event of a collision. For the more common shallow angle hits, the Jersey barrier is intended to minimize sheet metal damage by allowing the vehicle tires to ride up on the lower sloped face.
For higher impact angles, the Jersey barrier is a multistage barrier. The front bumper impacts the upper sloped face and slides upwards. This interaction initiates lifting of the vehicle. If the bumper is relatively weak, the front end starts to crush before any uplift occurs. Then, as the vehicle becomes more nearly parallel with the barrier, the wheel contacts the lower sloped face. Most of the additional lift of the vehicle is caused by the lower sloped face compressing the front suspension. However, wheel side-scrubbing forces provide some additional lift, particularly if the barrier face is rough. Therefore, exposed aggregate and other rough surface finishes should be avoided. Modern vehicles have relatively short distances between the bumper and the wheel; as a result, bumper contact is followed almost immediately by wheel contact.
It is only necessary to lift the vehicle enough to reduce the friction between the tires and the paved surface. This aids in banking and redirecting the vehicle. If the vehicle is lifted too high into the air, it may yaw, pitch, or roll, which can cause the vehicle to roll over when the wheels come in contact with the ground again. Concrete safety shape barriers should be adjacent to a paved surface so that the wheels cannot dig into the soil and cause the vehicle to overturn.
Modern variations include the Constant Slope Barrier, which has one constant slope from the base to the top, and the F-Shape Barrier. The F-Shape is similar to the Jersey Barrier in appearance, but has different angles and is much taller. The F-Shape is thought to be the best current concrete barrier design. It takes its name from a set of tested barriers that were assigned letters as identification. However, the F-Shape was not widely adopted as many jurisdictions were well-satisfied with the Jersey shape, which also met the crash-test criteria. In addition, their contractors did not want to change profiles because they had a considerable investment in the forms required to produce Jersey barriers.
The UK equivalent is the concrete step barrier.
The older guard rail barrier system did not prevent traffic from entering oncoming traffic. New Jersey first used concrete traffic barriers in 1955. The current shape was first implemented in 1959 as a result not of crash testing, but of police observation of the accident results of previously installed concrete barriers.
Jersey barriers have been used extensively by American forces in Iraq to fortify road-blocks and public infrastructure, along with modern "T" and "L" barriers, much taller variants.
Since 1990, the Canadian province of Ontario, a modified version of the Jersey barrier is employed on major freeways, such as Highway 401. Standing 4 feet tall and without internal reinforcement, they are often referred to as Ontario Tall Walls.
Jersey barriers were used in the wake of the Oklahoma City bombing and September 11, 2001 terrorist attacks to enforce standoff distances from federal buildings, monuments, the Sears tower in Chicago, and the Library tower in downtown Los Angeles.
Most commonly orange and white in color, plastic Jersey barriers provide high visibility to motorists, reducing the potential for collisions. They are often used not only for road work, construction zones, and water and sewer projects, but also for security at airports and garages (for access denial).