When a road passes through an enclosed area you could say it’s going through a tunnel, but what about if it’s under a short bridge or if there are windows on one side? A tunnel has a very specific definition in roading: it has to be at least 80m long. Tunnels 80-120m long are ‘short tunnels’ while tunnels longer than that are ‘long tunnels’. This means that when you pass under a motorway, even though it might be 40m, that’s an underpass, not a tunnel.<\/p>\n
However, there’s nothing to stop people or local authorities calling anything a ‘tunnel’ even if it’s less than 80m. Australia has a few long(ish) tunnels, e.g. the M5 which is 4km, but that pales into insignificance when you see tunnels from Scandinavia and Europe, the longest of which are more than 20km; in Europe, tunnels of 500m are considered long tunnels.<\/p>\n
Tunnel length is often considered in relation to the risks it poses to road users when passing through. The safest tunnels are single-direction tunnels where traffic flow is separated, but not all are like this.<\/p>\n
Tunnels are built as a shortcut through steep terrain or to allow buildings or other infrastructure to exist on top of them, e.g. the Tugun Bypass (M1)<\/a> where the extension to the Gold Coast airport runway creates a 334m tunnel.<\/p>\n