Many are probably completely unfamiliar with the highway features known as ‘runaway truck ramps.’ Based on a video recently posted to Facebook by Caltrans, they could be among the more important things people have never heard of.

Many are probably completely unfamiliar with the highway features known as ‘runaway truck ramps.’ 
According to Road & Track, these ramps are "essentially a short paved apron leading into a long chute of loose gravel. The resistance of the gravel brings the truck to a halt almost immediately..."
Based on a video recently posted to Facebook by Caltrans, they could be among the more important things people have never heard of. 
The footage shows a speeding big-rig roll onto one such runaway truck ramp and the vehicle to a complete halt in seconds. 
Presumably, the massive truck could not have performed such an act without the assist.
These gravel-covered ramps are generally located along hilly stretches, where travel speeds and stopping distances can be difficult to control.