Guardrails provide a barrier which prevents vehicles from entering specific areas. In some cases, guardrails can highlight a vehicle safety hazard, such as a steep slope or ditch. They can block off an area which has trees or other obstructions that could cause considerable damage to an oncoming car. A guardrail can be delineated to warn drivers in the dark and can slow, or even stop a vehicle before it passes the guardrail boundary into an even more significant mishap than that caused by guardrail damage.
In other cases, guardrails can define the edges of a commercial property without the need for a fence or separate enclosure, which can establish parking or other boundaries yet still allow wildlife free access.