Crash cushions, also called impact attenuators, are passive restraint systems and not designed to prevent an accident from happening. A crash cushion is designed to reduce the consequences of an accident by slowly decelerating an errant vehicle before it impacts a rigid roadside hazard. It is a means for "extending the time of the crash event", or simply decreasing the severity of the impacting by reducing the rate of deceleration. A car travelling at 100kph that impacts a rigid roadside object will come to a sudden violent stop. The passengers in the vehicle, who for a brief millisecond will still be travelling at 100kph, will then be thrown forward into some part of the car, the windshield, the steering wheel or hopefully a seat belt. Finally, all of the passengers's internal organs will impact his chest wall, causing internal bleeding and internal injuries. The deceleration levels will be incredible and the person will probably die. However, if this same car travelling at the same speed impacts a properly designed crash cushion instead of the rigid object, the results will be much different. The vehicle will be brought to a controlled, safe stop as the impact is extended over time. The passengers will experience far lower deceleration rates, and they will probably walk away from the accident. The first crash cushions were developed in the late 1970's in the United States. They consisted of empty oil drums that were systematically arranged in front of a roadside object. Modifications to this basic concept were made over the years. Instead of empty steel barrels, plastic drums filled with varying weight of sand were employed. Recent innovations in crash cushions include the Brakemaster System and the Low Maintenance Attenuator System (LMA). The Brakemaster System, introduced to the United States in 1990, utilises friction to safely decelerate the vehicle. This system is proving to be a very cost-efficient addition to the highway safety product mix. It is a low initial cost system with low re-usability. The LMA is just the opposite. It is designed for high frequency impact areas. Ninety-eight percent of this system can be reused after a typical impact. Refurbishment is quick, so workers are not exposed too long to traffic. Crash cushions have become a common site on roads in the United States.
Samenvatting