Reading Material

Train Operations　Ⅱ

Locomotive Hauled Trains

The traditional train comprises a collection of coaches（or freight wagons）with suitable motive power attached in the form of a locomotive.The train consists of sufficient vehicles to carry the traffic offering and provided with enough power for the job.For passenger operations，one locomotive is generally sufficient.In heavy freight operations，this number might go up to four locomotives on the front and at some other places along the train.

A good deal of flexibility is possible with locomotive haulage.As long as the train weight remains within the capacity of the locomotive（s），any number of vehicles can be attached，although limits will be imposed by platform or siding lengths.Locomotives themselves can also be flexible，many being designed to cover a range of duties.

The advantages for locomotive hauled trains mean they are the best choice for many railway operators around the world，especially freight but，where traffic is dense，i.e.where a large number of trains are required，a more rational approach is necessary，particularly at terminals.In addition，in very predictable operations like commuter services or metro lines，fixed formation trains will be the most efficient.

Terminal Operations

One disadvantage of traditional locomotive haulage shows up at the end of the line.When a train arrives at a dead end terminal，the locomotive is trapped between the train and the buffer stops.The only way to release the locomotive is to remove the train and a second locomotive is required.This second loco is attached to the other end of the train and will be used to provide power for the return trip.When the train has been removed，the first locomotive is released，moved away from the platform to a“loco siding”near the terminus and stored until used for the return trip of another train.This problem can be solved，if space is available.The train stops a distance from the buffer stops and a crossover to a run-around track is provided.This is sometime referred to as a“locomotive escape”and is used as shown in the Diagram 1.

Often，the adjacent platform track is used but it must be kept free of other trains.Sometimes a scissors crossover is used.Of course，the arrangement would not nowadays be suitable for a major city terminus where space is at a premium and land is very expensive，so efforts are madetouse tracksto the optimum.So，although locomotive changing operations at terminals are commonplace，where there is intense traffic，additional movements for loco changing can restrict the terminal capacity.Also additional locomotives are required to cover these terminal operations.To overcome all these limitations，the Multiple Unit was introduced.