The most common types of bridges are reinforced concrete walls or metal rails on concrete parapets. If improperly treated, the exposed ends of these railings can pose a rigid fixed object to errant vehicles. In most instances an approach guardrail is used to shield the exposed end and to prevent vehicles from travelling in behind the railing. Guardrail is typically more flexible than the bridge rails to which they are attached. A transition section is therefore required wherever there is a change in the deflection characteristics between the approach guardrail and bridge rail or between different barrier systems.