TUNNELS
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529.1 Tunnel ahead
May be used with diagram 572, 573, 575 or 773
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Figure 7-1 Name and length of tunnel on a motorway
When indicating a tunnel on an all-purpose road, the sign has black characters on a white background with a black border The sign is not prescribed by the Regulations and requires authorisation
7.4 The sign shown in diagram 529.1 is for use in advance of tunnels. If the tunnel is controlled by wig-wag signals, the sign should be supplemented by a plate to diagram 773 (see section 21).
7.5 The Road Tunnel Safety Regulations 2007 require that a tunnel’s length should be indicated on a sign at the portal. This should be done using a non-prescribed variant of diagram 2401 or 2928 (see figure 7-1 and para 1.5.). It is not appropriate to use diagram 529.1, where the supplementary plate indicates the distance ahead to the hazard.
LOW BRIDGES 7.6 Incidents in which road vehicles strike low bridges present a serious hazard to both rail and road users. There is a significant number of reported bridge strikes each year. It takes only a relatively small amount of force to displace bridge girders sufficiently to derail a train. Serious damage can also be caused to arch bridges. It is therefore particularly important that the signs and markings on low bridges are correctly installed and maintained to a high standard. The use of black and yellow hazard markings helps to make the vulnerable parts of a structure more conspicuous. The yellow parts of these markings may also be reflectorised, making them much brighter at night, and fluorescent. The latter greatly increases conspicuity in dull weather and at dusk (see para 1.33 for further guidance on fluorescence). However, fluorescence is visually intrusive and is therefore best confined to structures that are known to be at risk.
7.7 The standard minimum clearance over every part of the carriageway of a public road is 16'-6" (5.03 m). Where the clearance over any part is less than this, signs should be provided. Where a dual carriageway road has hard shoulders with restricted headroom, this should be separately signed, supplemented with the hazard markings in diagram 530.2 or the chord markings used at arch bridges (see paras 7.23 and 7.24).
MEASUREMENT OF HEIGHT
7.8 All bridges and other structures with a headroom of less than 16'-6" (5.03 m) should be clearly signed. The Regulations allow heights to be shown in either imperial units or both metric and imperial units. It is strongly recommended that both units are displayed on signs, especially on main routes and roads used frequently by foreign vehicles. Metric signs alone must not be used; either two signs or a combined metric/imperial sign must be used. Imperial and metric heights should be calculated separately.
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7014.1 Reduction in bridge headroom ahead
The height may be varied
7.9 The bridge height should be re-measured when works on the road or to the bridge might have affected the available headroom. Permanent signs should be changed if necessary and a temporary sign to diagram 7014.1 may be erected for a period of 6 months following completion of the works.
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