What those cables in highway medians actually do in the event of a crash – Jalopnik

The history of highway medians is long, and today’s cable medians are a relatively new phenomenon if you keep that in mind. They first became popular as a way to prevent accidents in the 1960s, with the three-strand arrangement – ​​developed by the New York State Department of Transportation and featuring cable attachments on the traffic side of the poles – leading the way. But the idea of ​​traffic dividers dates back at least to the year 1300, when Pope Boniface VIII created what may have been the world’s first physically separated ‘road’ over Rome’s St. Angelo Bridge, a popular route for pilgrims during the Jubilee of the Catholic Church. For safety, the Pope had booths placed in the middle and had the crowd cross on one side of the bridge and return on the other.

The first divided highway in the United States is often considered to be Savery Avenue in Carver, Massachusetts, which had a green space with trees between the lanes. Of course, that was more of an aesthetic choice than a decision based on safety. The push for better wire barriers to prevent accidents in the US appears to have started with the introduction of the concrete ‘jersey’ barrier in 1946 – specifically developed to reduce the number of head-on collisions on a particularly steep stretch of road in California.

Currently, concrete barriers, metal guardrails and cable barriers are all used as protective devices, but each has its advantages and disadvantages. Today we will talk about the latter. Keep in mind that, just like those ugly concrete walls on the highway, or those black and white stripes, there’s more to center barriers than meets the eye.

The biggest advantage of cable center barriers is of course safety effectiveness. The North Dakota Department of Transportationfor example, reports that they can “reduce cross-median crashes by 97%.” The Federal Highway Administration indicates 92% fewer mid-range fatalities, 93% fewer frontal fatalities, and 94% fewer multi-vehicle crashes traveling in opposite directions. (It’s also worth noting that cable barriers can increase some other types of accidents, although this risk can be reduced somewhat by combining them with rumble strips.)

What certainly helps is that the cable is not as stiff as concrete barriers or crash barriers, transferring the forces of a crash sideways rather than back to the people in the car. The cable does much the same for the car itself, catching it like a net instead of bouncing back into the potential path of other vehicles.

Cable style center barriers can also be cheaper to install. An investigation of the Washington State Department of Transportation – which took into account costs such as sales tax and procurement costs – showed that for the same expenditure 2.4 times as many kilometers of cable barriers could be installed than concrete ones. As for so-called affordable guardrails, they can actually be more expensive in the long run. Some of this could be influenced by the fact that cable systems are significantly easier to install on slopes and hills than the alternatives – which also don’t perform as well in those locations. Cables will also not allow snow and ice to build up as they do with concrete barriers.

As mentioned, one of the stranger effects of using cable-mounted median barriers is that while they generally reduce the number of fatalities resulting from head-on collisions, they can actually increase the number of overall crashes. Like the Federal Highway Administration It was noted that a study of North Carolina highways found that installing median barriers led to an increase in the number of crashes in which a vehicle veered off the left side of the highway, struck a stationary object, or had a rear-end collision.

Furthermore, despite the initial low installation cost, this is far from a one-off situation: one thing that increases the effectiveness of cable barriers is that the poles they are mounted on are relatively weak, and they are specifically designed to bend or break as part of the way they absorb crash forces – meaning they sometimes need to be repaired or replaced even after a single impact.

Cable barriers also work best in combination with wide central reservations. After all, they can deflect up to 12 feet when struck by a vehicle, and that can still be enough to bridge the gap between oncoming lanes on the highway, resulting in a head-on collision, and that’s even if the barrier works as designed. To provide some context here, for a “high-speed, fully controlled access road”, such as POINT it says, which sees fewer than 20,000 vehicles per day, the median must be at least 50 feet wide to allow for driving without a median barrier. Barriers are recommended where the center line is less than 30 feet and the roadway has an average of 20,000 vehicles or more daily traffic, and a cost-benefit analysis is suggested for locations with the center line between 30 and 50 feet.