This week's 'Ask Evan' question deals with safety wires installed on area highways. Mark S in Shippensburg asks, "PennDOT" is installing barriers in the median along I-81 that resemble 4 foot wire fences. My question is why are they on only one side of the median and why aren't they in the middle of the median?
PennDOT recently installed what are called cable media barriers or CBM's. It is also known as a high tension CBM because the wires stretch from end to end, According to PennDOT, nationally, they are considered a better way to prevent cross-over crashes than putting in something permanent like concrete barrier or trees or something similar. The reasoning is that a vehicle will be 'caught' in the heavy-duty wire and slowed down to the point of not being able to go across a median. Hitting something permanent means hitting something that won`t 'give' in the way the CBM will 'give.'
PennDOT admits the CBM may not stop a fully loaded tractor-trailer that maybe be going over the speed limit from crossing-- but it may at least slow it down. On the other hand the CBM may not be as helpful to a motorcycle rider that hits it. There is some inherent danger emergency crews that come in contact with it in the event of a crash. However, many emergency responders have been trained as well to deal with the potential danger of a cable snapping while they are trying to free occupants of a vehicle.
CBM's are never placed in the middle of a median, and never on both sides. The side where it is placed is determined through scientific methodology.
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