One of the most frequent questions we get around here is “What’s the difference between gating and non-gating crash cushions?” It all has to do with clear zones. Your next question is probably, “Well what’s a clear zone?”
So before I answer non-gating vs gating let’s talk a little bit about clear zones. A clear zone is the area behind a crash cushion that is free of trees, cliffs, swamps, etc. It is of traversable slope, meaning, if you can open your car door and not fall over, then you are probably ok. The area is normally 75 ft long and about 20 feet wide. This area is meant to be a run off area for errant vehicles.
NCHRP 350 Test Matrix For Gating Crash Cushions
So what is non-gating and gating? Gating is term used to describe an attenuator that is designed to allow an errant vehicle to enter a clear zone where it can safely decelerate before coming into contact with a hazard. NCHRP Test 33 and 32 above are gating tests.
When the vehicle comes in contact with the attenuator, the attenuator folds away (or gates) to allow the vehicle to safely pass. Gating attenuators are more economical than non-gating so if there is enough clear zone you should be using attenuators of the gating variety.
NCHRP 350 Test matrix for gating crash cushions
Non-gating attenuators as you can imagine, do not allow the vehicle to pass though when impacted at the front to of the system. True or false, a clear zone is not needed when a Non-Gating crash cushion is installed. FALSE. A clear zone is still needed, It is just smaller. Your high school physics teacher will be able to tell you that when a vehicle comes into contact with an attenuator at 15 degrees at a high speed the vehicle will most likely pass behind the system. A non-gating crash cushion can’t stop this from happening, but it can slow the vehicle. Non-gating attenuators are normally used in medians and on the side of the road when a full clear zone can not be achieved