7.16 At arch bridges, where the available headroom is indicated by signs to diagram 532.2, 532.2A, 532.3 or 532.3A, an alternative route may be signed using a sign to diagram 818.5, at the x-height indicated in Appendix A. As with mandatory height restrictions, the sign should be placed where the driver can see it in good time to make the necessary manoeuvre and full route continuity signing should be provided.
NON-ARCH BRIDGES
7.17 Mandatory signs should normally be used at non-arch bridges, as they can give more effective protection than warning signs. Traffic regulation orders are not required for mandatory height limit signs at a bridge, tunnel or similar structure over the highway (see direction 7(3)), but are required for limits imposed for environmental reasons.
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