This will be a new mini-series within this blog, discussing various aspects of a high performance railway, often called Metro, in simple-to-understand terms. Hope you enjoy.
The main purpose of a Metro is the efficient transport of passengers on trains. Only logical then to look at requirements for trains first, what they need to feature to support a high performance metro operation.
Quantity over quality?
The obvious requirement for a high capacity train is to maximise the train’s capability for carrying more passengers. Some railways in Australia used to form six-car trains by coupling two three-car sets, or eight-car trains by coupling two four-car sets. The downside of that were the two vacant train cabs in the middle where the two train sets are coupled. Not only could no passengers be fitted in the space needed for the middle cabs, and the coupling, it also does not allow passengers and service personnel to walk the entire length of the trains.
In the future, the increasing patronage numbers will mean that a railway operating six-car trains will want a single six-car formation, without the lost space for middle cabs and coupling between shorter train sets. This alone will lead to a higher number of passengers which can fit in the train, and it also increases safety as service personnel can roam freely along the entire length of the train.
Another way of increasing the passenger capacity of a train is reducing the number of seats. A standing passenger simply has a smaller footprint than a seated one, so the more standing space the train has the more passengers can fit in. Obviously there is a balance to that, because passenger comfort requires passengers to be seated for longer journeys. The ratio of seated vs standing passengers on a train is specific to the railway, its journey time and the railway’s standards for passenger comfort. For example, a 500 metre people mover connecting two airport terminals requires only very little seating provision due to its very short journey time (but lots of space for luggage).
Faster speed transitions
Strong acceleration and braking is another key element of increasing performance of the metro. When the transitions between stopping at stations and travelling at line speed get minimised, the overall journey time decreases and passenger travel is more efficient. When a fast-accelerating train can leave a station quicker, the next train can follow sooner, which reduces the ‘headway’ (time-distance between following trains, measured in seconds) and increases the line capacity measured in the number of trains per hour. (Note that capacity and headway are inverse factors).
The balance required here is that acceleration and braking need to be smooth enough so that passengers are not falling about on the train. An important criterion in this is the “jerk”, which defines the change in acceleration or deceleration (braking is basically a negative acceleration).
Doors are critical
An often underestimated criterion for new trains is the number and width of doors per carriage. With more and wider doors the passenger exchange at stations (passenger leaving the train, plus passengers on the platform boarding the train) can be more efficient. This reduces the need for the train to dwell at the station platform, which again reduces the headway and hence improves line capacity. It baffles me that some new train orders in Australia still come with only two rather narrow doors per carriage (on each side, obviously), and those trains will certainly struggle with any requirements for shorter passenger exchange times in the future.
Not just the number and width of train doors are important, also the walkways for passenger to get to those doors. Larger vestibule areas around doors and rather wide aisles with longitudinal seat layout helps the passenger movement on the train. See my previous caveat around the ratio of seating and standing space on trains. The current B-series trains in Perth provide a good mix of longitudinal seating near doors (also providing priority areas for wheelchairs and prams) and 2×2 seating in the middle of carriages.
Trains need to run
Lastly (at least for this post), a train must be able to run without interruption to be at its maximum efficiency. Downtimes for planned maintenance intervals are prudent, but when in service the trains should provide exceptional service availability.
