New trains for Great Western and Scotland at Hitachi's new Newton Aycliffe plant

After rail privatisation, passenger mileage increased from 18bn to 40bn up to 2016.

Although almost 6,000 coaches were built over this time, most replaced those that did not meet crashworthiness standards, so the fleet increased by only 18% and trains became crowded.

At last this situation is changing. Since 2015, train operators have placed large new train orders owing to cheap finance, franchise specifications emphasising quality, and new trains having lower maintenance and running costs. Some new franchises are replacing the different fleets they inherited with one standard type. In addition, the Department for Transport has procured new trains for the Great Western and East Coast main lines and Thameslink, while Transport for London did the same for the Overground and Crossrail.

Hence 13bn is being invested in 7,000 rail passenger vehicles, which is about half the March 2018 fleet size of 14,025 coaches. This will provide longer trains on much of the rail network, but not where the system is at capacity and trains are already the maximum platform length.

Nevertheless, in such circumstances new trains can provide extra capacity, for example by removing body-end electrical cubicles and providing wider gangways. New trains also improve service reliability when designed to maximise doorway passenger flow to reduce station dwell times and provide improved facilities for passengers with reduced mobility, power points, wi-fi, and less vibration.

Being laden with sensors, they should also be more reliable. This, together with condition monitoring stations at depots, provides remote condition monitoring to detect potential faults and unexpected wear rates. This also facilitates a more cost-effective condition-based maintenance regime.

The increase in fleet size will be less than half the new vehicles ordered. The industrys 2018 long-term passenger rolling-stock strategy predicts a 2024 fleet size of between 15,508 and 16,725 vehicles, say an additional 2,700. Although new trains will replace life-expired vehicles, this strategy estimates that their introduction will result in 4,000 surplus vehicles.

Owing to the high cost of keeping surplus vehicles in an operational condition and the need for 50 miles of sidings on which to store them, it is likely that most surplus serviceable vehicles, 800 of which are less than 20 years old, will be scrapped. These include electric trains that are now surplus due to cancelled electrification schemes.

The successful introduction of these new trains requires new or altered depots, training drivers, other train crew and maintenance staff, as well as ensuring infrastructure compatibility and possibly platform extensions, electrification work and timetable alterations.

All the above, together with the complex task of commissioning and securing safety approval for new trains, stretches available experienced personnel. New train fleets often do not work straight out of the box and infrastructure interface issues can be problematic, for example electromagnetic compatibility between trains and signalling. The new generation of trains also have software-controlled systems managing typically 5,000 functional requirements. Software unreliability during the testing can be an issue. One fleets software was at version 33 before service approval.

For these reasons, the forecast service entry dates of these new fleets are typically a year late. This can result in short or cancelled trains when existing trains are sent to other operators before the new ones enter service as the cascade of rolling stock displaced by new trains is based on contracted service entry dates. Late train commissioning can compress train crew training programmes, resulting in cancellations from staff shortages.

This glut of new trains is good news for passengers. Although they will have lower operating costs, procuring rolling stock on a feast-and-famine basis disjointed from the electrification programmes comes at a cost. Furthermore, this also threatens companies that specialise in life extension and overhaul.

Also under threat when the inevitable famine comes are the train builders which, in some cases, have built new UK factories. Current rolling-stock procurement is just one illustration of the need for a stable long-term railway strategy.

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Glut of new rolling stock brings challenges and opportunities for rail sector - Professional Engineering