Most people take the partitions that divide the traffic on highways for granted. But these seemingly simple barriers are actually deceptively sophisticated: Their designs have been well-tested and tweaked to ensure driver safety on both sides of the road in the event of a crash. The most common name for these ubiquitous concrete slabs is Jersey barriers—but why?
The California Connection
In the era before Jersey barriers, roads were divided by guardrails made of wooden beams, which were flimsy and therefore didn’t prevent cars from crashing into each other. As more and more vehicles took to the roads, it became clear that a better solution was necessary.
Concrete road barriers were first used in California in 1946, where they replaced the wood beam guardrails on the treacherous Grapevine section of the state’s Ridge Route highway—the home of the original “Dead Man’s Curve”—where the roads had a 6 percent downgrade that led to many head-on collisions. The parabolic barrier on the median of the road proved to be successful in reducing accidents.
Three years later, the state of New Jersey adopted comparable concrete structures and installed preventative parabolic median barriers on the Jugtown Mountain section of U.S. Route 22 in Hunterdon County, which had a similarly hazardous downgrade to the Ridge Route highway. These original barriers measured 19 inches high and 30 inches wide, with 2 inches buried in the road to provide stability. Each was anchored to the roadbed by steel dowels and consisted of a 2-inch thick outer layer of white concrete to make it more visible at night.
How Jersey Barriers Got Their Name
Though the initial barriers were somewhat successful in reducing the impact of collisions, New Jersey state highway engineers continued to tinker with the design, creating progressively larger prototypes based on amounts of observed accidents (as opposed to performing controlled crash testing).
Eventually, in 1959, they settled on a standard barrier height of 32 full inches above the pavement with a 24-inch-wide base. The base is 3 inches high and is followed by a 13-inch side slope before the barrier becomes vertical. These barriers were implemented in various states, and though the design would be tweaked—for instance, by the creation of a 42-inch tall design for trucks—the barriers still carry with them the name of the state in which they were developed.
Jersey Barriers vs. F-Shape Barriers
Jersey barriers are designed to redirect a crash, using the car’s momentum to absorb the impact and slide the vehicle up parallel along the side of the barrier to prevent a rollover. In high-speed crashes with small cars along Jersey barriers, however, there is a greater likelihood that the car will roll over, so an alternate barrier was created.
According to the Federal Highway Administration, the F-Shape barrier has the same 3-inch-high base, but features a side that slopes 10 inches above the pavement—three inches less than the side slope of the Jersey Barrier—and is thus able to better absorb proportional impacts from smaller chassis to prevent a rollover.
Though the F-Shape is generally preferred, the use of Jersey barriers—as well as other barrier designs, including constant slope, single slope, and vertical—are still acceptable, because they adequately pass crash tests administered by the National Highway Traffic Safety Administration. These types of barriers have found uses beyond roads, too, whether it’s on construction sites, near important buildings, as flood walls, or in spots where erosion needs to be controlled. There are even light, portable plastic versions.
A version of this story ran in 2013; it has been updated for 2023.