Roadside barriers are used to protect traffic from roadside obstacles or hazards, such as slopes steep enough to cause rollover crashes, fixed objects like bridge piers, and bodies of water. Roadside barriers can also be used with medians, to prevent vehicles from colliding with hazards within the median.

A barrier can be a natural or constructed obstacle to movement and may define the boundaries of a facility. The purpose of a barrier is to prevent the penetration of an area by intruders. A road barrier is a component which prevents passage into a dangerous area, commonly used to mitigate risk.