Stepping Back

Terminal Occupation

Terminals are usually located in densely occupied areas and often date from an era when land was cheaper than it is now. Opportunities for expansion are limited so, for busy terminals, efficiency of operations is very important. It is essential that trains do not occupy a platform for any longer than necessary to unload the arriving train and prepare it for departure.

Trains may require cleaning and/or reprovisioning whilst in a terminal platform, since the old practice of removing a train from the arriving station at the end of every trip, cleaning and restocking it for catering requirements and returning to service for a later trip, is inefficient. Toilets may also be drained and provided with clean water in terminals, if special facilities are provided. Diesel refuelling is generally done away from the passenger areas.

Track layouts at many terminals are complex and compact, due to the shortage of space. Flexibility of operation requires careful design of the layout and short run-in and run-out times. Restrictions due to signalled protection systems for dead ends will restrict train movements at peak times. A peak hour platform occupancy of more than four trains in the hour is unlikely for long distance services. Main line terminal operators would think they were doing well if they could get a platform utilisation of three, long distance EMU trains an hour in a dead end terminus like Victoria (London).

For metro operations, terminals are usually small and can accommodate a much higher frequency of trains. No dwell time is lost at peak times because of cleaning or catering. A two-platform terminus with a scissors crossover of suitable speed (as provided for Central, Hong Kong MTR) can allow a service of 34 trains per hour to be reversed if special crewing arrangements such as "stepping back" or "double-ending" are used.

This is a crew change system used at a two-track, island platform terminal to reduce train turnround time. When the first train arrives, the driver shuts down the cab and alights. Another, waiting driver, immediately enters the cab at the other (departure) end of the train and "opens up" the cab ready for departure. The first driver, meanwhile walks to the departure end of the opposite platform. When a train arrives in that platform, he enters the rear cab, waits for the arriving driver to shut down his cab and then prepares the rear cab for departure. When this is done the train is ready for departure. It should not be confused with double-ending. It has been used at, for example, Brixton (Victoria Line, London) and Central Station (Tsuen Wan Line, Hong Kong MTR) to good effect.

Дата добавления: 2014-01-11