16 September 2010

The endcap on a highway guard rail

I never understood that they had any functional significance, until I read a thread at Reddit today.  The reason for the endcap is that when you hit it, it is supposed to peel the railing off the posts like a ribbon:
If the endcap is missing, or malfunctions, or something goes wrong, then the vehicle winds up looking like a giant shishkabob:
The bottom two photos come from this story:
I assisted at this accident yesterday north of Deer Lodge on I-90. The driver was appx 22 year old guy heading east to College. He had left central Washington early in the morning. He fell asleep at the wheel and drifted off the shoulder hitting the end of the section of guard rail.

The guard rail came through the right headlight, engine compartment, firewall, glove box, passenger seat, rear seat and exited out the driver’s side rear window. That is 120 LF of guard rail that threaded through the Suburban.

[There were] no passengers and the driver was not injured.
More photos at the link.


  1. I had no idea. That is very cool (and somewhat frightening).

    I've been told that the large barrels that are grouped together as endcaps for jersey barriers on the highway are indeed barrels, and they're full of water. The idea is that if they're hit, the car's momentum will go into displacing a couple tons of water rather than straight into the barrier. (Splash instead of crunch.)

    They should really set up some barrels for one barrier on a road we affectionately call the 'Maple Valley Speedway', it's been hit at least four times. They get it rebuilt just in time for it to get crunched again.

  2. I've seen smashed barrels that were filled with sand.

    Sand has several advantages over water for this kind of application. Sand can't evaporate, it won't leak out a tiny opening, and as long as it's dry, it won't freeze solid.

  3. Interesting. I wonder how this compares to the German system of "rising" rails.

    Unfortunately, I could not find a better picture than this one:


  4. Richard, I've seen those "rising" rails here in the U.S. as well. I think I'll do an informal survey next time I take a long trip.

  5. Here in the UK, I've only seen these endcaps on motorway dividers in recent years. Before that, we had rails that sloped downwards at the ends. I'm guessing the sloping rails probably caused more damage than they prevented, as the endcaps seemed to be deployed at a rapid pace.

  6. Yeah, those are all great until you hit one on a motorcycle. Then it's game over.

  7. Here's what it looks like when a car hits the rising rail ('Leitplanke'): http://www.da-news.de/2007/07/28/schon-wieder-auto-auf-leitplanke-gefahren/

  8. The flat endcaps are favored instead of the rising or sloping ends (from the ground) because the rising ones will just flip the car over. Since guardrails are especially used when there is a big embankment or dropoff on the other side...

    And modern cars are designed with crumple zones to absorb an impact with something like the end cap (along with the breaking and bending guardrail)

  9. I don't understand why they don't just curl the end sideways until it is like 10 feet off the edge of the road. Then there is no rising end and no blunt end to hit.

  10. They can do that "curve the rail way off to the side" where there is room, and a fairly level surface. But if there's a slope, or a sheer drop or cliff face... Sand Barrels seems to be the best alternative, with one of the 'peeler' endcaps hidden at the back.

    And note that the first barrel only has a foot of sand in the bottom, and the rest behind it are progressively fuller. This is to make it nicer for the motorcycles and Smart Cars.


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