Train Performance Issues on Metros and Light Rail

Train Performance Issues on Metros and Light Rail

Generally metros and light rail systems only carry passengers and there is not therefore the added complication of ?mixed' traffic. Sim cases, there is no segregation of express and stopping trains to complicate matters. The main concern is to provide trains which will closely match demand at various times of the traffic day in the most economic manner. The main issues therefore are:

•What capacity is required at various times?

•What are the achievable acceleration and deceleration rates?

•What   ?dwell   time'   is   required   at   stations?

•What top speed is necessary?

•How can energy be conserved in normal running conditions e.g. by coasting?

•How much scope is required for recovering lost time in the peak due to delay?

•For light railways only, what additional factors need to be taken into consideration for any lengths of track which are incorporated into the

highwayand   where   ?shared   running'   takes   pla

Once all these considerations have been fully investigated, decisions can be made on the type and number of different units of rolling stock that is required to run the railway. To this there must be added extra stock to allow for the fact that there will always be some vehicles on programmed repair and maintenance as well as others out of service for unplanned reasons or mishaps. With modern rolling stock and proper maintenance procedures, this extra proportion should be able to be kept to not more than a quarter, depending on the size of fleet.

It can often be shown that a small amount of extra capacity, both in tractive effort and braking, can play dividends in the long run and allow overall economies in energy.

For relatively short distances between stops, the timetable for trains running normally should allow for a pattern of motoring up to maximum allowable speed and then coasting for a period before braking for the next station. This pattern is less demanding on energy than flat-out speed and maximum braking which can howeverbe resorted to if lost time needs to be regained due to delay.