Several variations of concrete road dividers were introduced from time to time under various names, ever since the first model was successfully deployed in the year 1946, on the Grapevine Grade, a risky mountainous stretch on the US route 99 in California. These first experimental models were precast, concrete parabolic median barriers, 26 inches high and 28 inches wide and weighed 3000 lbs.
However, the name Jersey barriers became known only after New Jersey highway engineers installed them on the accident-prone Jugtown Mountain section of U.S. Route 22 in rural Hunterdon County. The 19 inches wide and 30 inches wide barriers with parabolic concave faces on either side would clear the mudguards if the vehicle swiped against it; and the smooth parabolic concave surface would redirect the errant vehicle back into the traffic flow without bringing it to a sudden halt. However, though the number of accidents reduced, they still occurred when trucks scaled these barriers.
After experimenting with several specifications of height and width on the median barriers, New Jersey highway engineers noticed the reduction in accident rates, using taller barriers. They finally settled on the 32 inches high and 24 inches wide parabolic median concrete barriers in 1959, and other state highways followed suit to adopt these measures, which remained the standard specification for barriers for many decades.
Past decades saw the introduction and deployment of different types of barriers and the search for the perfect barrier continues. Here is a look at the innovative designs on median barriers, some of which continue to be in use.
GM barriers or GM shape: These barriers were the first ones to be crash tested before deployment. However, because smaller cars tended to roll over after impact with the barriers, this design was discontinued.
California K-Rails: K-Rails are temporary concrete barriers for work zones but if installed using pins- loops connections and 4 stakes, these may be semi-permanent structures for a period of 2-5 years. However, removing the barriers from paved surfaces is expensive and exposes workers to risks.
F-shaped barriers: These barriers are almost identical in function to the Jersey barrier and the only difference is the break point; which is lower in the F-shape barrier and sits at 10 inches from the road as compared to the 13 inches break point of the Jersey barrier. The low breakpoint in the F-shaped barriers reduces lifting of the vehicles and reduces chances of roll over, but the Jersey barrier continues to be the most favored design for crash tests and meets the criteria laid down by the Federal Highway Administration.
Constant slope barriers: Simple vertical barriers do not lift vehicles, so there are no chances of a roll over; but the flip side is the possibility of sheet metal damage to the vehicle, injuries to the occupants and the vehicle is not redirected on to the road. Texas and California have developed the constant slope barriers with increased heights, wider bases. The Texas constant slope barrier stands at 42 inches with a constant slope that makes an angle of 10.8 degrees to the vertical at ground level; the California type 60 constant slope barriers have a height of 56 inches and slope at an angle of 9.1 degrees to the vertical.
Crash tests reveal that these perform as well as the New Jersey barriers and F-shaped barriers respectively. The new safer designs incorporating the increased height specifications, inexpensive installation and unchanged performance of constant slope barriers even after road resurfacing makes them a favorable choice. These barriers are now being deployed as permanent structures.
Heavy vehicle median barrier: The New Jersey Turnpike Authority ( NJTA) effectively crash tested a 42 inches high median concrete barrier using NJ shape forms, with heavily reinforced tops having a thickness of 12 inches. The vertical reveal is covered with asphalt to anchor the barrier firmly so it does not overturn on impact. Heavy vehicles like tractor-trailers are contained and redirected upright on to the road with these barriers.
Concrete Step Barrier: High performance concrete step barriers are approved for roads in the UK and Ireland. This model of median barrier developed in Holland has several advantages such as zero crossover incidents, reduced fatalities; low maintenance cost, maintenance free for 50 years, and can contain all types of vehicles.
Ontario Tall Wall: Way back in 1968, highway authorities in Ontario, Canada crash tested this taller version of the New Jersey barrier at various test levels and it was way ahead of its time then. Gradually over the years as larger vehicles hit the roads, the barrier heights increased to 42 inches. Another feature of this tall barrier was that it cut off glare from oncoming vehicle headlights.
Plastic Jersey barriers: Rotationally molded plastic Jersey barriers replaced concrete median barriers, where it was necessary to deploy the barriers temporarily for short periods at work zones, building construction sites, water and sewer projects, during natural disasters to regulate pedestrian and vehicular traffic. The barriers made from pretreated, heavy-duty polyethylene are able to withstand inclement weather conditions and require almost zero maintenance. Other important features that make these barriers popular are portability and lightweight. These barriers are easily stackable making transportation and assembly an easy task. However, for added strength sand, water or any other ballast materials are filled into the barriers. The brightly colored plastic Jersey barriers are highly visible and adequately warn of any imminent danger.
The Federal Highway Administration allows usage of plastic Jersey barriers along with the necessary reinforcement kit as replacement for concrete barriers, only after these have been crash tested at the specified test levels. Otherwise, these plastic barricades are linked end-to-end, to form a wall and used as channelizers to direct pedestrian traffic or for guiding vehicular traffic near work zones. These are used as barricades for crowd control at event, races, as security installations at airports, parking areas, government buildings and to prevent access to any specific area.
In general, Jersey barriers, both plastic and concrete structures have helped in reducing the number of accidents on highways, roads, and work zones. Moreover, research continues to discover designs and materials that will ultimately give us the perfect barrier; until then the Jersey barriers will continue to dominate our highways.