Reference · road & bridge standards

Road restraint systems on bridges

The purpose of a vehicle restraint system where there is a drop.

A vehicle restraint system — a parapet or barrier — is provided where a vehicle leaving the carriageway would face a hazard such as a drop or watercourse. Its adequacy is assessed against the height of the drop and the consequence of a vehicle passing it. Where a historic structure predates modern standards, the question is not that it must meet them, but whether a documented, costed, scheduled repair to it was carried out.

Source: Design standards for road restraint systems (DN-REQ-03034 and related). Stated for reference.

A reference page explaining a published road or bridge standard. It states the standard only; it makes no claim about any particular location.

Last updated 2026-08-05. This is a living record — findings are added as dated entries and prior versions remain visible.