396 ITU‐T's Technical Reports and Specifications The following considerations should be accounted for in designing utility tunnels: Wet utilities should be separated from the dry utilities and installed in a separate compartment Tunnels should be designed as a walk‐through system providing walkway access, and allowing for removal and replacement of valves, expansion joints etc. Tunnels may typically have a height of 1.9m or more. See Figures 15 and 17 which are from ITU‐T [b‐27]. The example shown in [b‐1] is 4m high. Tunnels may typically have a width of 0.7 m or more. See Figures 15 and 17 which are from ITU‐T [b‐28]. The example shown in [b‐1] is 4m wide. Figure 4 – Example of utility tunnel [Source: Abu Dhabi Utility Corridors Design Manual, b‐ 1] Tunnels should be accessible through on‐grade entrances with sloped hatches and sloping walkways Tunnels should be properly ventilated; ventilation shafts should be constructed at a minimum spacing of 50‐75 m or as deemed necessary based on actual tunnel dimensions. NOTE – Different countries may have other national standards or regulations.