The Jersey Barrier

courtesy of kelly a. giblin2006_1_27

They line the medians and shoulders of highways in every state. Since September 11, 2001, they’ve also helped safeguard our buildings from terrorist attacks. And just last summer they were seen being deposited into the breaches of the compromised floodwalls surrounding New Orleans. These omnipresent wedges of concrete are universally referred to as “Jersey barriers.” But they actually made their first appearance on a treacherous stretch of California mountain highway in 1946. In the 60 years since then, a huge engineering effort has gone into their development. Those humdrum concrete walls that dominate today’s highway landscape are actually highly refined pieces of safety equipment.

The “Grapevine Grade” was the most hazardous portion of California’s famous Ridge Route highway, home to the original “deadman’s curve.” The highway was reconfigured in 1934 to improve the mountainous traverse, which had a more than 4,000-foot elevation change. But still, as U.S. Route 99, it contained terrifying grades. The Grapevine was a curving 6 percent mountain descent on a highway linking Los Angeles and the fertile San Joaquin Valley that daily carried an average of 6,500 vehicles, a quarter of them trucks.

To prevent head-on collisions, wood-beam guardrails on steel posts were installed to separate the lanes of the Grapevine. But these wooden barriers were frequently damaged by truckers, who found them convenient as a supplemental means of braking, brushing up against them on downhill runs. And they proved no match for vehicles hitting them at wide angles. So the Grapevine Grade had a much higher than average incidence of fatal head-on collisions, and in 1946 the California Division of Highways decided to install an experimental parabolic concrete median barrier there.

These first concrete barriers were made in precast 26-inch-high, 28-inch-wide, 10-foot-long sections weighing 3,000 pounds each, and looked a lot like the ones found on highways today. Steel forms were used to give them as smooth a surface as possible. They were hollow, with internal steel reinforcement, and had iron anchors to hold them to the ground and “cat’s-eye” reflectors on both sides to help drivers navigate. Carried to the installation site on flatbed trucks, they were hoisted into place and bolted to the concrete roadbed with small gaps between them to allow for drainage.

The U.S. 99 installation was successful not only in deterring truckers from using the barriers for braking but also in preventing collisions. It got a write-up in Engineering News-Record , an influential and widely read publication, yet more than 20 years passed before events on the opposite coast prompted California highway engineers to return to the concrete median barrier.

Which is where New Jersey comes in. Highway officials in that state would spend the next 15 years developing the design that eventually spurred the nationwide adoption of the device.

New Jersey installed its first concrete median barrier in late 1949. The curving Jugtown Mountain section of U.S. Route 22 in rural Hunterdon County had, like the Grapevine Grade, seen many head-on accidents over the years. When the roadway was upgraded to four lanes in 1948–49, the State Highway Department decided to try an experimental method of separating the traffic. State Highway Department engineers explored several different configurations before settling on a 19-inch-high, 30-inch-wide curb with concave parabolic faces on each side. It was, as Engineering News-Record reported, “designed to clear the mudguards and running boards of cars that sideswipe the curb and to deflect automobiles back onto the roadway without a sudden stop that might result in injury to passengers or damage to the vehicle.”

Only 16 of those 19 inches extended above the surface of the pavement; the rest was buried to provide stability. One-inch-diameter steel dowels anchored the curb to the roadbed. Unlike the Grapevine Grade barrier, the U.S. 22 one was formed and cast in place, on site. Its most innovative feature was its 2-inch-thick outer layer of white concrete. New Jersey highway engineers had found that white Portland cement was much more reflective than standard gray cement—almost two and a half times more visible at night.

courtesy of mike ballard2006_1_29

New Jersey’s barrier met with some success reducing head-on collisions on Jugtown Mountain, but trucks occasionally scaled the device. So state highway engineers continued their research, and in 1955 another prototype, now reaching 18 inches above the road surface, was installed along Route 4 in Bergen County. Four other kinds of barriers were also tried: wire cable, steel beam, concrete beam, and a 12-inch-high vertical curb. The 18-inch parabolic concrete barrier performed the best. A follow-up test the next year used a 20-inch-high parabolic barrier with a 30-inch-wide base installed on a section of U.S. 22 in urban Essex and Union counties. That barrier reduced the number of head-on collisions from 15 in 1955 alone to only one over the following three and a half years, and injuries fell by 75 percent.

The 20-inch design was installed on almost 75 miles of highway over the next few years, but the occasional vehicle still managed to surmount it. New Jersey highway engineers went on to experiment with a 24-inch-high barrier before finally settling on a standard height of 32 inches, with a 24-inch-wide base, in 1959. These changes were based just on observations of how the barriers did, not on any program of crash testing. This caused the state some headaches down the road. Lawyers representing drivers who had accidents on sections of highway with the old 16or 24-inch-high barriers sought to find the state liable for not having replaced them with the 32-inch barrier.

The 32-inch-high “Jersey” barrier would become the standard concrete barrier design for decades, and it’s still in wide use today. It nonetheless took years to be commonly adopted. The main reasons were cost and questions about whether any kind of median barrier actually improves highway safety.

The November 1959 Engineering News-Record carried a story on the installation of steel guardrails on the median of the New Jersey Turnpike at a cost of $40,000 per mile. The article stated that Turnpike Authority officials were “not certain” they were “justified” in making this expenditure because “the conflicting results of barrier studies throughout the country” showed that “while median barriers reduce the number of fatalities resulting from accidents, they increase the number of accidents and injuries.” New York had reported a 35 percent reduction in the overall accident rate on the Hutchinson River Parkway when barriers were installed, and San Francisco found a similar reduction on the Bayshore Freeway; but two Los Angeles freeways had shown 75 to 88 percent increases in the accident rate and 53 to 116 percent increases in the injury rate.

Median barriers might have been getting mixed reviews, but fatal cross-over collisions continued to increase on roads that didn’t have them. In 1959 a California Division of Highways study found that 20 percent of all fatal highway accidents were the result of going across the median. Moreover, the explosive growth in traffic between 1950 and 1970 wasn’t matched by additional rights of way in densely populated urban areas, and even in suburban and rural areas land acquisition could be prohibitively expensive. Often the only way to gain more space for traffic was by encroaching on the median. Of course this made crossover accidents ever more likely, and highway engineers around the nation began to look for solutions.

Most of those engineers spent their careers toiling anonymously at state or federal transportation agencies while advancing the state of the art in highway design. This was not a field with a dominating personality behind it. The nearest thing to one was Charles M. Noble, who headed New Jersey’s State Highway Department between 1946 and 1949, the period when the earliest version of the Jersey barrier was developed. Noble led a colorful life for a highway engineer, spending the early part of his career working under the great bridge designer Othmar Ammann on the construction of the George Washington, Goethals, and Bayonne bridges and then becoming a lead design engineer for the Pennsylvania Turnpike, America’s first superhighway. He commanded a construction battalion for the Seabees in World War II, serving in China and the Aleutians and often working behind enemy lines. He left his post as New Jersey’s state highway engineer in 1949 to become the chief engineer for the construction of the New Jersey Turnpike, and he later headed the Ohio Department of Highways.

national crash analysis center/national highway traffic safety administration2006_1_30

In the early 1960s General Motors and the Texas Transportation Institute of Texas A&M University developed what would become known as the GM barrier, crash-testing late-model cars at the GM Proving Grounds. And California, whose 1959 study had originally recommended steel cable or guardrail barriers over concrete ones, revisited the matter because the former were so expensive to repair. Steel barriers were comparatively cheap to install but suffered so much damage from collisions that they ended up costing more than concrete, as well as endangering drivers and repair crews until they were fixed.

The California Division of Highways conducted numerous tests of the Jersey barrier between 1965 and 1968, crashing radio-controlled automobiles at various speeds and approach angles. Its study concluded that “the New Jersey concrete median barrier is an effective, low-maintenance design,” and California installed about 6 miles of it in three trial projects in 1969. On the basis of the success of those trials, over 130 miles of the Jersey barrier had been added to California highways by 1972, and other states had followed suit. Nationwide, 19 states had adopted the Jersey by 1975, and another 8 took up the GM version. Concrete median barriers lined more than 1,000 miles of U.S. highway.

The average motorist has no idea how sophisticated these barriers are. Their primary function is obviously to separate opposing flows of traffic. But their wedge design was developed to minimize the severity of accidents by restoring control of a vehicle on impact. In a shallow-angle collision—a sideswiping—the Jersey barrier lets the front tire ride up its lower angled face and gets the vehicle back on the roadway with minimal damage. In higher-angle impacts, the car’s front end or bumper first hits the upper sloped surface of the barrier. As the front end begins to collapse, a slight lifting action occurs, reducing the friction between the tires and the road surface. Shortly thereafter the front tire makes contact with the lower sloped face of the barrier, causing some additional lift as the vehicle is redirected toward the road.

The main differences between the Jersey barrier and later variations like the GM shape, the F shape, and the Ontario Tall Wall are the height of the “break point” between the upper and lower slopes, as well as the width and overall height of the barrier. The standard 32-inch Jersey barrier has a 3-inch vertical reveal at its base; a 10-inch lower sloped surface angled at 55 degrees from the roadway; and a 19-inch upper sloped surface angled at 84 degrees from the road, so the break point sits 13 inches up from the road. (The 3-inch reveal at the base is there solely to allow for future roadway resurfacing.)

The GM barrier had a 2-inch reveal, then a 13-inch lower slope at 55 degrees, and a 17-inch upper slope at 80.4 degrees. The 15-inch-high break point worked well with the large cars used in the crash tests in the early 1960s, but with smaller cars it was found to cause excessive lifting and thus a tendency toward instability and rollover. New installations of the GM shape had ceased by the late 1970s.

The F shape, so named because it was the sixth configuration tested in a 1976 Federal Highway Administration study, has only a 10-inch-high break point. Its lower slope has an angle of 55 degrees; its 22-inch upper one, 84 degrees. The difference between it and the Jersey is subtle, but the F shape’s lower break point leads to reduced vehicle lifting and better overall performance. Nonetheless, it has not unseated the Jersey barrier. The Jersey still meets Federal Highway Administration standards, and installers have made a large investment in equipment for it.

Some highways use simple vertical barriers. Unlike sloped ones, they don’t lift vehicles, so they’re less likely to cause rollover. But damage to the vehicle is often greater, as is the likelihood of occupant injury, and redirection of the vehicle into the roadway is less predictable. The advantages of the vertical wall barrier are simpler, less expensive installation and unchanged performance after roadway resurfacing. Hoping to combine the lower cost of the vertical barrier with the safety of the Jersey, the states of Texas and California have developed “constant slope” barriers. These are 42 (Texas) and 56 (California) inches high and have a wide base that tapers upward at a constant angle, rather than a break point. Roadway resurfacing never degrades their performance, and the single slope simplifies manufacture. The Texas Constant-Slope barrier has an angle of 10.8 degrees from the vertical; the California Type 60 barrier, 9.1 degrees. Crash tests have shown that the Texas Constant-Slope barrier performs much like the Jersey, and the California Type 60 much like the F shape.

The 42-inch-high Ontario Tall Wall barrier is a taller version of the Jersey. It was developed by the Department of Highways in its namesake Canadian province after it conducted crash tests of the Jersey in 1968, and it was ahead of its time. The growth in vehicle size over the past decade has forced most state highway departments to rethink the height of their barriers, as the 32-inch-high design has proved somewhat vulnerable to sport-utility vehicles and oversize trucks on today’s highways. While the 32-inch barrier remains the Federal Highway Administration minimum standard, New York, Massachusetts, and even New Jersey have adopted the 42-inch. It not only contains vehicles with higher centers of gravity but also does a better job blocking headlight glare from taller vehicles going the other way.

How well do they work? The need for the Jersey barrier and its brethren may seem obvious today, but for more than 40 years there was no definitive study to prove it. Studies of installations on individual roadways had had varying results, and testing had always focused on what exactly happened during an accident, not on the performance of the barrier concept as a whole. The Federal Highway Administration didn’t even formally adopt a standard for this “roadside hardware” until 1993. That standard, named NCHRP Report 350, was developed by the Transportation Research Board of the independent National Research Council.

In evaluating median barriers, Report 350 examines three criteria: structural adequacy (the barrier’s ability to withstand a crash); occupant risk (the likelihood of death or injury after the crash); and postimpact vehicular trajectory (how well the car gets back on the road). The standard evaluates only impact performance, not cost-effectiveness, aesthetic appeal, maintainability, durability, or the effect on overall highway safety.

But in 1992 the American Automobile Association and the National Science Foundation co-sponsored a study by the Institute of Transportation Studies of the University of California at Irvine that concluded that concrete median barriers decreased the frequency of fatal highway accidents by 36 percent and the frequency of highway fatalities by 43 percent. They also decreased accidents resulting in injuries by 13 percent and injuries themselves by 11 percent.

Not surprisingly, the study found that head-on accidents have been “decreased significantly” on highways with concrete median barriers, with no deaths reported from such collisions. The study estimated that over the projected lifetime of a concrete median barrier, the benefit-cost ratio would be about two to one even by the most conservative measure. The only unwelcome finding was that both injury and noninjury accidents increased (9.2 and 2.4 percent, respectively) when new lanes were added along with the barriers, narrowing the median, though fatal accidents still decreased by 31.3 percent even in these cases.

The search for the ideal concrete median barrier continues. In the 1990s the Texas Transportation Institute developed a wide, low-profile portable barrier for use in construction zones. The design includes a reverse slope, tapering in toward the base, to push vehicles downward so as to prevent them from jumping it into the work area, while its lower profile provides greater visibility. Will it replace the Jersey barrier in work zones? History suggests it won’t. So far the stalwart has been supplemented but not supplanted. The new and improved designs that would replace it have failed to do so. The F shape could not overcome the Jersey economic advantage; the Constant Slope could not match its vehicle stability characteristics. So that ubiquitous concrete presence on highways across the country, born in California, will live on as the Jersey barrier.