For those of you who have never seen one of those runaway-truck-ramps in action, or how they actually work, here's an interesting video. Typically they are found on steep mountain descents, particularly when the descent is relatively straight without a lot of sharp curves. They are designed to stop very heavy trucks, in a reasonably-safe manner, with brake-problems or other defects which can cause loss of speed-control down the grades. There are a number of them in the Appalachians, one of the most well-known being on the famous Uniontown, PA descent on U.S. 40 down Summit Mountain and its 3.5-mile 10% grade....I've mentioned that descent a couple times in the past. This video is not of that exact ramp, but illustrates how they work in general.





Here's the one at Uniontown:

 

always been tempted to live out my evel knievel dreams when i see these on the highway!
it's always that, auto transporters when loading/unloading, and flatbed tow trucks !

 

I wonder how often those ramps actually are needed.

 

I've seen a couple of semis use them in my lifetime and all I can say is thank goodness they were present. Really terrifying to see a semi beginning to lose control down a very steep descent with turns ahead.