Due to its fortress-like location in the Alps, Switzerland possesses one of the world’s most elaborate tunnel networks.In fact, the country's surfaced tunnel network is 220 strong. Back in 2001, when two trucks collided in the St. Gotthard tunnel – the world’s third longest tunnel – the resulting fire killed 11 people. It was the worst tunnel disaster in Swiss history.Since then the country has embarked on a massive civil engineering programme to resurface the country’s tunnels with fire-resistant mortar. So far 126 of the 220 Swiss tunnels still require come re-engineering. The work is taxing, especially moving typically ungainly civil engineering equipment. Fortunately, the Swiss have found Mercedes-Benz’s legendary Unimog off-road workhorse well up the task.A classic former Swiss army U 406 Unimog, built in 1971, has proven an outstanding logistics solution for tunnel engineers. Convert to a road-rail application it is employed as a railway 'engine' and dutifully pulls 60t of equipment daily through the 1.2km Cassanawald tunnel, which is currently undergoing resurfacing. A deployable rail-wheel set enables the Unimog to ride on a carriage track when necessary, then depart on a normal road surface - rolling its massive off-road specification tyres. Tunnel engineers usually contact Swiss rail operator SBB to help out with moving equipment, yet in narrower confines normal road users are severely penalised with delays when this method of equipment delivery is employed. The Unimog's ability to tow equipment on both road and rail navigating the narrow H13 route which runs through the Hinterrhein valley (where the Cassanawald tunnel is located) has proved invaluable, allowing traffic volumes to increase when most of the day’s tunnel resurfacing equipment has been delivered. Operating at an altitude of 1 600m, engineers have been hugely impressed by the ‘Mog’s performance, no doubt aided by its reduction ratio transmission. Not bad going for a 40-year-old vehicle running a 62kW 5.7l in-line six diesel.