Trowse Bridge

Trowse swing bridge is a single-track railway bridge which carries the Great Eastern Main Line over the River Wensum just outside Norwich in the United Kingdom at grid reference TG245076.

The bridge was originally built in 1845 by George Parker Bidder, was rebuilt in 1905 and again in 1986. Like many swing bridges, the structure first lifts on hydraulic jacks before swinging open to allow the passage of water traffic. The bridge has frequently caused problems with navigation on the river due to its unreliability, leaving it unable to open.

It is notable for being the only swing bridge in the United Kingdom to carry an overhead electrified railway track (25kV 50Hz). Other examples can be found along the Northeast Corridor in the United States; see for instance Portal Bridge, and the Galata Bridge over the Golden Horn in Istanbul. The power supply to trains is provided by an overhead conductor rail instead of a wire, and there are short lengths of overhead conductor rail either side of the bridge on the fixed approaches. There is a 40 mph (64 km/h) speed limit over the bridge in both directions as trains are about to arrive at, or have just departed from, Norwich Station.

The bridge is also the home of Trowse Signal Box, which controls most of the Bittern Line from Whitlingham Junction to Sheringham. The line was resignalled in 2000, leading to the closure of a number of mechanical signal boxes with control moving to Trowse, although it is arguable if this is a real improvement since there have been a number of serious failures causing full or partial suspension of service during electrical storms. This is due to the system using high frequency pulses in the rail as opposed to standard track circuits to operate level crossings. The resignalling saw the end of one of the few remaining sections of single track main line controlled by tokens. The signalling meant Cromer Signal box that the last surviving M&GN example was decommissioned; however it has been saved as a museum.

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