Stock Balance

Rolling Stock Operation

Rolling Stock Calculations

We are now ready to calculate the rolling stock requirements. To find out how many trains are required to operate a regular interval passenger service, the following simple formula is applied:

Round trip time divided by the headway

In our Forest Line example above, the round trip time is 33 minutes and the headway is 3 minutes, so we need 11 trains to operate this service during the hour when there are 11,500 passengers travelling over the busiest section of line. Some railways keep a "service spare" train on standby, in case a service train becomes defective or a disruption to the service leaves a gap in the headway which needs to be filled temporarily. In this case we might plan to have 12 trains available for service and we will have to add one or two extra to cover maintenance requirements.

After the peak hours, the numbers of passengers will drop so the train service can be reduced to match. This will often mean, for a metro line, about a 40% or even a 50% reduction in the number of trains required. The planned train loading will usually be reduced during off-peak hours to allow a greater percentage of passengers to get seats, so the number of trains operating in off-peak hours may not match the patronage exactly as it does during the peak. Thus the load factor may be 50% or less.

The stock required to operate a regular passenger service will be calculated as we have seen above and then a series of "diagrams" or working paths for each train will be designed. These will take into account:

· the location of the depot

· the location of other stabling points

· the frequency of exterior washing required

· the frequency of maintenance inspections

· other routes where the trains can be used

A train will have to be given time to move from its stabling point to the first station where it is required to pick up passengers. Time will also be allowed for its return to a stabling position, its "dispersal". Trains used to cover a weekday metro or commuter service present complicated patterns of use which look like this:

All day use: AM start to night finish

Peak only: AM start to AM finish; PM start to PM finish

Peak and evening: AM start to AM finish; PM start to Night finish

Mid-day: AM Start to PM finish

Each train will be used on one of the above patterns, of which there will be several varieties.

Rolling stock must be "balanced" at the end of the traffic day and timetables must be designed to allow this. "Balanced" means that any place where trains start from (a depot or sidings) must have an equal number of trains restored to that location at the end of the day. Here is an imaginary example:

The Forest line (shown above) must provide 12 trains for the morning peak service each weekday - 11 for service and 1 spare. Of these, 7 are stabled at Ash Depot, 4 at Elm sidings and 1 at Oak siding. One of the four at Elm will form the spare train. Therefore, by the time the last train has stabled after the close of traffic, 7 trains must have got back to Ash, 1 to Oak and 4 to Elm. The timetables must be designed this way and crew duties have to be arranged so that people are available to start these trains up each morning. If there is a train short at any location because it was left at the depot for any reason, a trip or two will be cancelled while the crew goes "away from home" to fetch it. This is what it means when you hear that the service is disrupted because "trains were in the wrong places" in the morning after a serious problem.

Another point to realise is that it will be necessary to ensure that all trains return to depot within 2 or 3 days so that they can be washed and maintained. The balancing act must therefore ensure that the trains rotate through the depot in this 2-3 day period. Performing this balancing act is made easy by use of a technique known as diagramming. Before the diagrams are worked out, a timetable has to be prepared.

Дата добавления: 2014-01-11