Bridge Headrooms

Bridges over roads

The Design Manual for Roads and Bridges TD 27/05 “Cross-Sections and Headrooms” gives guidance on design headroom for new bridges in Section 6. Table 6-1 (reproduced below) indicates overbridge headroom is a minimum of 5.3 m, or 5.7 m for footbridges or structures vulnerable to vehicle impact.

Type of Structure New Construction Headroom (m) Existing Structure Headroom (m)
Overbridges \(5.30 + S\) \(5.03 + S\)
Footbridges, sign/signal gantries and other structures vulnerable to vehicle impact \(5.70 + S\) \(5.41 + S\)
Free standing temporary structures N/A \(5.41 + S\)
All Permanent Structures over High Load Routes \(6.45 + S\) \(6.18 + S\)

where \(S\) is the maximum deflection plus any construction tolerances.

Note that this headroom is to be maintained above any area a vehicle could feasibly reach, e.g. above footpaths and central reservations.

Bridges over railways

NR/L3/TRK/2049 gives clearances (in mm) for structures over railway lines

Figure 1: NR/L3/TRK/2049/MOD07 Table 1
Figure 1: NR/L3/TRK/2049/MOD07 Table 1