A guard rail is a safety device (usually a metal railing) that is placed along the edge of a roadway to prevent motorists from leaving the roadway. A guard rail typically either protects motorists from entering a steep slope, or it prevents collisions with static objects like trees or bridge columns located off the roadway. Averting collisons like these can save lives and prevent serious injuries. The guard rail absorbs the kinetic energy from the collision and redirects the vehicle back onto the road where it may come to a safe stop.
This is a typical guard rail application at the edge of a roadway shoulder:
A: The guard rail absorbs the impact of an errant vehicle that leaves the roadway and protects the motorist from hitting an obstruction. The anchored rail absorbs the brunt of the blow and can redirect the errant vehicle.
B: The guard rail blockout (made of wood or composite material) is typically 8 inches in depth and is between the guard rail and post. The blockout minimizes vehicle snagging on the posts and reduces the likelihood of a vehicle vaulting over the guard rail by maintaining the rail height during the initial vehicle strike.
C: The guard rail post (which may be either steel or wood) provides the overall support and stability for the guard rail system. The posts are designed to dissipate the energy of the vehicle in the collision.