Height restrictions

Where structures above the roadway, such as bridges or railway catenaries form a height restriction on the trafficable roadway, appropriate signs and markings should be installed to make road users aware of the hazard.

Signs

The signs used at height restrictions are shown in Table 6‑12.

For further information on railway crossing signs and diagrams refer to the TCD manual Part 9.

TCD manual Part 9

Table 6‑12: Signs for hazards that for a height restriction

Sign code	Example	Description/use
W13-3 Low overhead clearance advance warning		Should: be installed in advance of overhead tunnels or structures when an overhead soffit clearance is less than 4.4m; display the actual clearance to the nearest 1cm as determined by site measurement; have the measurement rounded down to two decimal places eg if measurement = 3.826m the indicated clearance shown is 3.82m. For single lane two-way roadway the measurement should indicate the minimum lane soffit clearance available over a width of 3m about the centre of the roadway. For multi-lane roadways, the measurement should indicate the minimum lane soffit clearance available over the full width of the trafficable roadway. For sign location, refer to note 1.
W13-4 Low overhead clearance - indication on structure or tunnel		Should be installed on the overhead superstructure of an overhead structure or tunnel where the overhead soffit clearance is less than 4.4m. Display the actual clearance to the nearest 10mm as determined by site measurement. For single lane two-way roadway the measurement should indicate the minimum lane soffit clearance available over a width of 3m about the centre of the roadway. Where soffit clearance varies over the 3m width, as at an arched tunnel or underpass, the W13-4 should be enhanced by supplementary reflectorised markings as shown in Figure 6‑8 to indicate the locations of the displayed clearance. For multi-lane roadways, the measurement should Indicate the minimum lane soffit clearance available over the full width of the trafficable roadway. For sign location, refer to note 2 below.

Table 6‑12 notes:

1. Should be:
   
   • placed near an intersecting road or wider part of the approach so that affected vehicles may detour or turn around;
   • installed so approaching road users have an uninterrupted view of it over a distance of at least 120m in rural areas and at least 60m in urban areas.
2. A pair of signs should be located:
   • overhead on the structure immediately above the soffit line to face approaching traffic from each direction, (as shown in Figure 6‑8);
     and
   • in a single lane situation (one-way or two-way) – directly above the centre of the road; or
   • in a two-lane two-way situation where there is a marked centre-line – directly above the respective lane for each direction; or
   • in a multi-lane situation – directly above the centre of the combination of lanes provided for each direction.
3. The sign should be installed either in advance of the hazardous height restrictions section (such as overhead tunnels or structures) by at least the distance shown in the table below.

   Operating speed	Distance
   50km/h	65m
   70km/h	100m
   80km/h	120m
   90km/h	140m
   100km/h	160m

Markings on structure

Where W13-4 Low overhead clearance – indication on structure or tunnel signs are installed on structures, a 200mm wide continuous retroreflective yellow line should be marked across the soffit profiles of the structure. Refer to Figure 6‑8.

Where the soffit is of variable height such as an arch structure, additional retroreflective white arrows should indicate the point where the clearance is a minimum. Refer to Figure 6‑8.

Figure 6‑7: Hazard marking at height and / or width restricted structures

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Figure 6‑8: Signs and supplementary markings on structure or tunnel (single lane roadway) with varying soffit height

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