guardrail

A guardrail, also called a safety barrier, is a system of rails and posts installed along roadsides, bridges, and other facilities to prevent vehicles from leaving the roadway, absorb impact energy, and reduce crash severity by redirecting vehicles along the barrier.

Guardrails are usually steel W-beam or thrie-beam configurations attached to vertical posts. Other forms include cable rail, box-beam, and concrete barriers. End treatments and energy-absorbing terminals are used to reduce blunt impact at the ends.

Design and standards aim to balance containment, redirection, and energy absorption. They follow regional guidelines such as the United States’ AASHTO LRFD and MUTCD, or European EN 1317. Crash testing programs, including NCHRP 350 and MASH, evaluate performance.

Installation and maintenance involve proper setback from the travel lane, adequate post spacing, and secure anchorage. Regular inspections check for corrosion, deformation, loose fasteners, and damaged end terminals, with sections replaced or repaired as needed to maintain performance.

Safety considerations include the potential for end terminals to cause hazardous impacts if struck at high speed, or for guardrails to trap vehicles in certain angles. Selection depends on traffic speed, volume, shoulder width, and adjacent hazards, with alternatives such as barriers or slope protection considered.