A guardrail is a device which is designed to promote public safety by preventing people or vehicles from crossing from an established trail or road into a dangerous area. Many people are familiar with the positioning of guardrails along dangerous stretches of road, but any type of barrier intended to prevent falls or injuries could be considered a guardrail. For example, many hiking trails have guardrails in areas where steep falls are likely. In general, a set of conditions must be met before the installation of a guardrail will be considered.

The design of a guardrail can vary, depending on how it is intended to be used. As a general rule, the guardrail takes the form of a long strip of strong cast metal attached to posts. The metal is stamped so that it has multiple ridges. When something hits the guardrail, the ridges crumple, spreading the energy along the length of the guardrail. The multiple posts prevent a collapse, unless the impact is extremely heavy or at very high speed. The impacted section will usually need to be replaced after the accident has been cleared. Guardrails save lives by preventing people from falling and absorbing the impact of accidents.

Although a guardrail is intended to protect the public, a number of safety concerns are associated with guardrails, particularly those designed to work with automobiles. The first is the “end treatment,” or the finish on the end of the guardrail. Formerly, guardrails were not capped or finished in any way, leaving a wedge of sharp steel at either end of the stretch of guardrail. If someone collided with the end at a high rate of speed, the guardrail could potentially penetrate the car, causing injuries or death. Most modern end treatments are curved or flattened, and designed to resist the impact slightly.

If the guardrail or end treatment is too strong, it also has the potential of thrusting the car back into traffic. Therefore, most guardrails are designed to absorb energy, rather than deflecting it. In addition, traffic engineers have to think about the height of a guardrail. A tall vehicle may flip over a low guardrail, but a motorcycle could slide under a high one. Therefore, the height must be carefully considered before a guardrail is installed.

In order for a highway guardrail to be installed, traffic engineers must determine that there is a serious risk of severe off road collisions. In an area with a history of collisions, the risk is clearly illustrated, and the stretch of road will be added to the list of areas needing guardrails. In other situations, engineers have to evaluate the surroundings of the guardrail, looking for a cliff or other sharp change in elevation, and considering season conditions like ice and snow. If the risk is deemed serious enough, a guardrail will be installed.