Cable barrier

A cable barrier, sometimes referred to as guard cable or wire rope safety barrier (WRSB), is a type of roadside or median safety traffic barrier/guard rail. It consists of steel wire ropes mounted on weak posts. As is the case with any roadside barrier, its primary purpose is to prevent a vehicle from leaving the traveled way and striking a fixed object or terrain feature that is less forgiving than itself.American Association of State Highway and Transportation Officials. Roadside Design Guide. Third Edition, 2006. Task Force on Roadside Safety, 2006. Also similar to most roadside barriers, cable barriers function by capturing and/or redirecting the errant vehicle.

Because these barriers are relatively inexpensive, as opposed to concrete step barriers to install and maintain, and are very effective at capturing vehicles, their use is becoming increasingly prevalent worldwide. By far, the most popular use of the cable barrier system occurs in the medians of divided highways.

Given the opposing directions of traffic on divided highways, cross median crashes are particularly severe. While median width plays a large role in the occurrence of these crashes, increased width alone does not eliminate them and quite often, the median must be shielded with a barrier. Cable barriers provide a cost-effective solution to the shielding issue.

The system is more forgiving than traditional concrete (Jersey) barriers or steel barriers used today and remains effective when installed on sloping terrain. The flexibility of the system absorbs impact energy and dissipates it laterally, which reduces the forces transmitted to the vehicle occupants.

Although cable barriers have been used since the 1960s it was not until the mid-1990s that many departments of transportation began to deploy them with any regularity.

In many countries of the European Union these cable barriers are not allowed to be used along highways as they are perceived to be especially hazardous for motorcyclists. However, a study of motorcyclist injury rates for several types of highway barrier did not find an appreciable difference in fatal and severe injuries between cable and W-beam barriers. Both were significantly more hazardous than concrete barriers but less hazardous than none.

Types

There are two types of cable barrier systems in use today, low-tension and high-tension. Each system has its advantages and disadvantages, but in general, a high-tension system has a higher initial cost with lower long-term maintenance costs and concerns.

Low-tension

During the expansion of cable barrier use throughout the 1980s and 1990s, the low-tension system was specified almost exclusively. This system is also called the “generic” system, referring to the fact that it is not exclusively manufactured by any single producer.

Low tension simply means the cables themselves are tensed only enough to eliminate sag between posts. Large springs at both ends of the cable run are compressed (according to temperature) to maintain the tension in the system.

When a vehicle impacts the low-tension system under normal conditions, the cable moves as much as 12 ft (3.7 metres) from its original location. This movement is known as the dynamic deflection.
Given the lack of tension in the system, individual installations, or “runs”, of cable are limited to 2,000 ft (600 metres) with an anchor assembly at each end.

Due to the low tension of the system, the cables tend to lie on the ground in the event that an impact damages multiple posts. As such, there is no residual safety value within the undamaged remainder of the 2,000 ft (600 metres) installation and that entire section of barrier will remain nonfunctional until repaired.

Despite these perceived shortcomings, low-tension cable barrier, until recently, was arguably the workhorse of the industry. Thousands of miles of the generic system remain in use today in countries worldwide.

High-tension

In appearance, high-tension cable is very similar to low-tension. In most other aspects, the two systems are very different.

High-tension cable consists of three or four pre-stretched cables supported by weak posts. Currently, all high-tension systems are proprietary