The available headroom sign is used to indicate the amount of space under different types of overhanging structures. The measurement shows space in both metric and imperial units to ensure all road users are aware of their vehicle limits. The Diagram 530A has no variations but can be used in combination.
Material: R2/RA2 reflective overlay on aluminium composite backing
height limit signs at a bridge, tunnel or similar structure over the highway, but are required for limits imposed for environmental reasons. 7.7.2. The sign to diagram 629.2A (S2‑4‑5, see Figure 7-11) should be mounted on the bridge, as a driver seeing a bridge with no height limit indicated might well assume the headroom to be at least 16’‑6”. It may also be placed at the roadside in advance of the bridge (in most cases a sign being required on each side of the road), but as it is an offence for drivers of over height vehicles to pass these signs, they should not be placed where they would prevent legitimately required access to premises or side roads. Even when diversion signing has been provided, it is still necessary to give proper advance warning of the height restriction. Signs to diagram 530A are not appropriate, as they give no indication of the prohibition. Diagram 818.4, with or without a diversion route should be used; it will sometimes be possible to indicate an escape route for drivers who have missed the diversion signs by siting this sign in advance of the last diversion or turning point before the bridge. If it is much further from the bridge than the usual warning distance indicated in Appendix A, another sign to diagram 818.4 may be required at the appropriate place. Diagram 818.4 may also be used to indicate a restriction in a side road by including an arrow on the sign (the legend “ahead” must not be used with the arrow).