Cable barrier
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.
The flexibility of the system absorbs impact energy and dissipates it laterally, which reduces the forces transmitted to the vehicle occupants.
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.
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.
When a vehicle impacts the high-tension system under normal conditions, the cable deflects as little as 8 ft (2.4 metres) from its original location.
The standard by which all roadside safety features are measured is contained within the National Cooperative Highway Research Program Report No.
NCHRP 350 evaluates safety hardware according to three general factors:[4] The system must contain and redirect the vehicle with no underriding, overriding, or penetration.
Test level three (TL-3) is probably the most common as it establishes safety criteria for both small cars and pickups at 60 miles per hour (97 km/h).
There is a great deal of anecdotal evidence, however, that many of these systems are performing at a higher level in the field capturing vehicles as large as semi truck-trailer combinations.
Given these relatively large deflections, cable barrier systems are not usually considered appropriate to shield fixed objects closer than 8 ft (2.4 metres) offset of the travelled way.
[7] In places, such as Arizona, there is indication that the state government agency in charge of highway regulation failed to follow proper installation procedures.
[citation needed] A major problem alleged, that reduces the effectiveness of cable barriers, is the installation below grade, especially around slopes or dips.
[9] Without any compensation for a slope in the median, a car can actually jump the top of a barrier, and therefore be exposed to a potential cross-over collision.
