Guard Cable

The purpose of high-tension guard cable is to prevent vehicles that have left the roadway from sliding across the median and hitting oncoming traffic. Head-on collisions are some of the most severe and deadly crashes on our roadways.

On Interstate 70 in 2002, there were 24 fatalities involving cars that crossed over the median. In 2007, a year after guard cable was completely installed on all of I-70, there was one fatality involving a cross-median crash.

High-tension and low-tension cables

Guard cable can Low-tension cable systems drop to the ground when they are hit and stay there until they are repaired. High-tension systems are designed to survive multiple hits and can be easily repaired by maintenance personnel.

Installation relative to traffic

The cable is installed eight feet from the inside stripe of the passing lane. The widest passenger vehicle for sale is 7.2 feet. The average car is less than six feet wide and the average truck is less than seven feet. Essentially, the width of another lane exists between the passing lane and cable system.

How guard cable works

The guard cable is typically installed lower than the passing lane of traffic. The cable is designed to absorb the majority of a vehicle’s momentum. When a vehicle leaves the passing lane, it travels down the slope. As it hits the cable, the cable deflects and absorbs the impact. At the cable’s maximum deflection of eight feet, the vehicle is typically 25 inches lower than when it left the passing lane. The vehicle will have little momentum left to travel back up the slope into traffic.

Motorcycles and the cable system

Structures installed on the interstate highway system, such as bridge railings, signs, and the cable system, must meet crash test standards established by the Federal Highway Administration and the American Association of State Highway and Transportation Officials. The standards are established based on the predominant vehicle types used on the highway system: enclosed passenger vehicles such as cars and trucks.

An unprotected motorcyclist is not part of the standard to which these systems are designed, so there is not a standardized crash test scenario that we can refer to that would accurately predict the behavior in this type of accident.

Guard cables during winter weather 

Winter driving in Missouri is always challenging. Motorists can travel too fast for conditions, lose control, and slide into the median during snow and ice events. While some vehicles slide to a stop in the median, depending on the depth of snow and ice and the hardness of the ground underneath, occasionally a vehicle will slide across into the opposing lanes of traffic. The ability of opposing traffic to stop or avoid a collision in the same conditions that led to the first motorist leaving the pavement is marginal at best. Given those circumstances, the severity of the crash could be substantially reduced if a vehicle hits the cable.

Guard cable repair and replacement after a crash

MoDOT used state and federal funds to pay for the installation. Now that installation is complete, motorists are responsible for damages to the guard cable system. Much in the same way motorists are responsible for damages caused to other vehicles or property in collisions, any individual who causes damages to the guard cable system must pay to repair the damages.