The longitudinal flow ventilation system by Jet fan (booster fan) of Okuda Tunnel

In Okuda Tunnel on the Kitakyushu Urban Expressway, the jet fan made by Voith, West Germany (internal diameter: 630 mm; total length: 4.7 m), was first adopted in Japan as the longitudinal mechanical ventilation system. This jet fan was in service from 1966 to 1975. The tunnel air ventilation system that is best suited for the road conditions unique to Japan, where there are many mountainous areas and dense populations, is currently adopted for most (more than 80%) road tunnels in the country.