The Highway Crash Cushion

I’ve done my share of highway driving. From road trips to visiting my parents, I am experienced in the ways of the fast lane. Whenever I drive, I normally see a number of plastic barrels at the choke points on exit ramps. Not all exit ramps have a barricade of plastic barrels but the ones that would cause a significant damage to a vehicle and its driver do. I’ve seen more than a handful of movies where a car smashes into these barrels spewing water in its wake. To what effect I wonder do these water-filled barrels actually slowly down an out of control vehicle.
The answer is, quite a lot. Water barrels have been estimated to have saved around 17,000 lives since their initial installation in the 1960s. We have John Fitch to thank for that. Not the John Fitch who invented the steamboat in 1787, although he is his descendant. Fitch was a race car driver known for inventing many safety innovations for the race track and highways, including the plastic barrel barriers now known as the Fitch Barriers.
Race car Fitch’s invention was inspired by the sand-filled fuel cans surrounding his tent in WWII. The cans were strategically placed to protect against strafing runs. He later took these to the racing tracks after seeing a few nasty crashes firsthand. He filled a number of plastic barrels with sand and colored them yellow with a black lid. These were used as barriers to slow down cars before they crashed against the metal railings.
Barrel barriers are usually arranged in a diamond formation to ensure a car will hit at least some of the barrels in the event of a crash. The tip of the diamond has the least amount of sand/water and each successional barrel will carry a little more. I’ve also seen a straight line format but I trust the highway engineers with the strategics of the formations, depending on a particular exit.