---
title: "Traffic Barrier"
url: "https://commonwaysystem.org/patterns/elements/traffic-barrier/"
id: "ELM-TRB-23"
description: "A longitudinal barrier (guardrail, concrete barrier, or similar rigid or semi-rigid structure) installed to redirect an errant vehicle away from a roadside hazard or opposing traffic, rather than allowing the vehicle to travel further off-course."
updated: "2026-09-26"
---

# Traffic Barrier

`ELM-TRB-23`

Situational / Discouraged Element

Traffic Barrier

A longitudinal barrier (guardrail, concrete barrier, or similar rigid or semi-rigid structure) installed to redirect an errant vehicle away from a roadside hazard or opposing traffic, rather than allowing the vehicle to travel further off-course.

## Related Media

The items below come from outside the Commonway System, external videos, podcasts, and articles related to this page's topic, not part of the guidebook itself.

Aligned

### [Why America Won't Copy Sweden's Cheap Highway Fix](https://www.youtube.com/watch?v=jyNEnYaBszk)

Safe By Design

Explains Sweden's 2+1 alternating-passing-lane cable-barrier retrofit and the specific AASHTO Green Book barriers (literally) that have kept the same fix from scaling in the US.

## Why this pattern exists

Certain roadside conditions (a steep slope, a fixed object, an opposing travel lane with no separation) pose a severe risk if an errant vehicle reaches them; a traffic barrier is deployed specifically to intercept and redirect the vehicle before it does, at the cost of introducing its own fixed-object risk if struck directly. This pattern exists to document when that tradeoff is justified.

## Key considerations

-   Should only be installed where the hazard being shielded is more severe than the barrier itself, since the barrier becomes a fixed object a vehicle can strike[1]
-   End treatments matter significantly; an unshielded or improperly terminated barrier end can be more dangerous than no barrier at all
-   Height and strength must be matched to the design vehicle and speed of the roadway it protects, crash-tested against current standards[2]

## Related patterns

[Crash Cushion/End Terminal](https://commonwaysystem.org/patterns/elements/crash-cushion-end-terminal.md) (ELM-CCT-24) (the treatment addressing this pattern’s exposed ends); [Bollard](https://commonwaysystem.org/patterns/elements/bollard.md) (ELM-BOL-25) (a related but functionally distinct barrier type)

## References

1.  Legal / regulatory [American Association of State Highway and Transportation Officials, _Roadside Design Guide_, 4th ed.](https://store.transportation.org/Item/PublicationDetail?ID=1802)
2.  Legal / regulatory [American Association of State Highway and Transportation Officials, _Manual for Assessing Safety Hardware_ (MASH), 2016.](https://store.transportation.org/item/publicationdetail/2707)