The Lopper I Rail Tunnel is a railway tunnel in central Switzerland. The tunnel connects Hergiswil in the canton of Nidwalden with Alpnach in the canton of Obwalden. It forms part of the Zentralbahn Brünig line, which links Lucerne with Interlaken and the Bernese Oberland, between Hergiswil station and Alpnachstad station. It is 1,186 metres (3,891 ft) in length, and carries metre gauge (1,000 mm or 3 ft 3 ³/₈ in) track electrified at 11 kV AC 16 2/3 Hz using overhead catenary.