Highway Guard Rail · 2026-06-03

Highway Guard Rail Height and Deflection (Working Width)

By Metal Beam Barriers Technical Desk · Highway Safety Engineering · Auroguard Private Limited

Two dimensions decide whether a guardrail works: its mounting height and its deflection (working width). Here is how MoRTH and IRC:119 treat both.

Two dimensions decide whether a highway guard rail actually performs on impact: how high the rail sits, and how far it deflects. Both are governed by MoRTH Section 800 and IRC:119.

Height. The rail must present its full corrugated face to an impacting vehicle at bumper height. For a W beam, the top of the rail is generally held around 700–760 mm above the carriageway or paved shoulder; a Thrie beam, with its deeper section, follows the height set by its containment-level design. If the rail is mounted too low, a vehicle can override it; too high, and a small car can underride. Consistent height along the run — checked at every post — is a basic inspection item.

Deflection and working width. A flexible guardrail is meant to deflect on impact — that deflection is how it absorbs energy and softens the crash. IRC:119 quantifies it as working width, classified W1 (up to 0.6 m) to W8 (up to 3.5 m): the total lateral distance the system may occupy at peak impact. The design lesson is spatial: you must have at least the working width of clear space behind the barrier line, or a deflecting rail (and the vehicle behind it) can still reach the very hazard the barrier was installed to shield.

How to control deflection. Reduce post spacing (2 m down to 1 m), choose a stiffer profile (Thrie beam), or increase embedment — each lowers working width where clear space is tight.

Everything sits on the standard build: IS 2062 steel, 3 mm rail, hot-dip galvanising to 550 g/m², reflectors per IRC:35 / IRC:79.

Metal Beam Barriers manufactures highway guard rail systems and can advise the post spacing and profile that meet both your height and working-width constraints. Send your cross-section for a factory-direct quotation.

The systems this guide covers

MBB-5045

Road Safety & Highway Barriers

Highway Crash Barrier

Highway crash barrier systems designed and manufactured as per MORTH and IRC specifications for highways, expressways, bridges and medians. Available in W Beam and Thrie Beam configurations with hot-dip galvanised finish for maximum durability and road safety.

View product

MBB-2613

Road Safety & Highway Barriers