Terminals, Loops and Turnbacks

There are three ways of turning a train requiring to reverse its direction at the end of a trip. First a simple change of direction where a locomotive is placed at the other end of the train or, where driving cabs are available at both end of the train, can be achieved in a train in a single terminal platform with a track on either side as shown left.

Second, you can drive the train around a loop track beyond the terminal station - provided you have the space to build the loop (diagram left).

Finally, you can provide a reversing track (or turnback, as it is called in the US). The train deposits arriving passengers in one platform and goes forward to the siding where it changes direction and then proceeds into a departure platform. In the diagram below, a single reversing track is shown at the left hand end while the double set of reversing tracks are shown at the right hand end. The latter is the usual option and can be seen in such places as Paris Metro and Tokyo Underground and London.

The first option - a simple reversal procedure - is the most popular since it uses least space and is reasonably quick. For the second option, tram or light rail operators who equipped their trains with a cab at one end only favour the loop. Some metro operators also use it, notably Paris and New York.

The third option is a reversing or turnback track as shown above (left hand end) but it is often used also when turning trains at a location mid-route. The siding is provided beyond the station between the main running lines and is connected to both, as shown below.

This solution is popular for urban and suburban systems where the inner section of a route has a requirement for a higher frequency service than the outer section.

An alternative layout is where a two-track terminus has its tracks extended beyond the station (diagram above). This arrangement allows trains to be stored between the peak hours or at night. A defective train can be stored there until it can be repaired or sent back to the depot.

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