Components, systems and materials › Road furniture and safety › Thrie-beam crash barrier
Thrie-beam crash barrier
What it is
A thrie-beam barrier is a steel guardrail with a three-corrugation rail, deeper than a W-beam, mounted on posts with spacer blocks to contain and redirect errant vehicles.
Where it is used
Locations needing higher containment than a W-beam: bridge approaches, medians on high-speed roads, hazards close to the carriageway and routes with many heavy vehicles.
How it works
On impact, the deep rail spreads load over more posts and acts in tension like a beam and cable; posts bend and the spacer blocks keep the wheel away from the posts, so the vehicle is redirected rather than snagged or launched.
Types
- Single-sided and double-sided (median) thrie beam
- thrie beam with rub rail
- transition sections from W-beam to thrie beam to rigid barrier
Materials
Hot-dip galvanised steel rail, posts and spacer blocks; high-strength bolts and splice plates; end terminals.
A system is chosen by required containment level and working width, proven by full-scale crash tests to a recognised standard. Length of need is set from the hazard and approach speed. Transitions to rigid parapets need stiffening so vehicles do not pocket. Height is set above the finished road level and kept after overlays.
Installation and QA steps
- Set out line and length of need.
- Drive or set posts to the specified depth and spacing.
- Fix spacer blocks and rails with laps in the direction of traffic.
- Tighten splice bolts to the specified torque.
- Install crash-tested terminals and transitions.
- Check rail height after resurfacing.
- Laps installed against traffic, creating snag points
- unproven transitions to concrete barriers
- height reduced by later road overlays
- missing bolts or damaged rails left unrepaired
Codes cited
- IRC:119 (India): Guidelines for traffic safety barriers.
- EN 1317 (series) (Europe): Road restraint systems: performance classes and impact test methods.
- AASHTO MASH (USA): Manual for Assessing Safety Hardware: crash test procedures for roadside hardware.
Cited by number only. We do not reproduce code text, tables or figures.
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