British Rail Class 172

The British Rail Class 172 is a British diesel multiple unit (DMU) passenger train built by Bombardier Transportation's Derby Litchurch Lane Works for use on inner-suburban passenger services. The class is currently operated by West Midlands Railway.

The Class 172 is part of the Turbostar range, similar to the Class 168, Class 170 and Class 171.

Technical details and variants

There are four sub-classes:
* Class 172/0 - two-car, non-gangway train sets with West Midlands Railway for use on the Snow Hill Lines and Leamington Spa to Nuneaton, originally with London Overground.
* Class 172/1 - two-car, non-gangway train sets with West Midlands Railway for use on the Snow Hill Lines and Leamington Spa to Nuneaton, originally with Chiltern Railways.
* Class 172/2 - two-car, gangway train sets with West Midlands Railway for use on the Snow Hill Lines and Leamington Spa to Nuneaton.
* Class 172/3 - three-car, gangway train sets with West Midlands Railway for use on the Snow Hill Lines and Leamington Spa to Nuneaton.

The 172/0s and 172/1s resemble the existing ''Turbostar'' trains in not having end gangways. These trains have a maximum speed of .

The Class 172/2s and 172/3s used by West Midlands Trains resemble the , , and ''Electrostars'' by having end gangways to allow access between units. These trains have a maximum speed of .

The 172/0 were built without any onboard toilets in common with other London Overground stock. Toilets were retrofitted when transferred to WMT.

The Class 172s feature BSI (Bergische Stahl Industrie - Autocoupler) couplers which allow them to work in multiple with , units and most other units with the same coupler.

Differences from other Turbostars

The Class 172 trains are lighter than other Turbostars due to use of the Bombardier FLEXX-ECO bogies - a development of the B5000 bogies used on the Class 220 ''Voyager'' DEMU trains, rather than the previous 'Series 3' bogies. Another difference is that they have half-height airdams as opposed to the more standard full height airdams. They also differ from earlier Turbostars in having mechanical transmission rather than hydraulic - gear changes can be distinctly heard as the trains accelerate and decelerate.

Differences from Class 150

Class 172s have fewer seats than the s they replaced, but greater overall capacity due to the increased room for standing passengers as well as wider aisles intended to speed boarding and alighting and reduce waiting time in stations. The trains are air-conditioned and have no opening windows, unlike the Class 150s.

The Class 172 is designed to a body length, as opposed to the length used on previous Class 150 Sprinter DMUs - increasing capacity.

Operators

West Midlands Railway

West Midlands Trains operate a total of 39 two-car and three-car units, 27 of which had been ordered by predecessor London Midland, who originally planned for them to enter service by the end of 2010 on services to and from Birmingham Snow Hill, replacing Class 150s. The original West Midlands Trains sets have revised front ends with end gangways which make the trains look like the Electrostar family of units.

From 1 September 2011, the units started operating on the Snow Hill Lines with some weekend work from Birmingham - Hereford. When first used in service, the units suffered a fault with engine vibration in the passenger cabin, which has since been rectified.

The units were originally meant to replace all of the Class 150s, however three were retained.
Between late 2018 and early 2019 the London Overground 172/0s moved to West Midlands Railway, operated by West Midlands Trains, to replace the remaining Class 150s for transfer to Arriva Rail North and Class 153s operating on the Coventry–Leamington line and the Coventry to Nuneaton line as well as providing extra capacity on the Snow Hill Lines.

Former operators

London Overground

London Overground operated eight two-car Class 172s on the Gospel Oak to Barking line, replacing the old stock. The units were originally meant to be in service from February 2010, but due to production issues and then what were thought to be exhaust problems (which proved to be a false alarm), the trains entered service only in July 2010, and at reduced capacity due to staff training problems. By December 2010 the whole fleet was in service, allowing the Class 150s to be cascaded to First Great Western.

The success of London Overground's operation of the Gospel Oak to Barking Line meant that the 2-car Class 172s eventually proved insufficient in terms of capacity. Initially, there were plans to replace them with 3- or 4-car DMUs. Later, the government announced plans to electrify the line, with the intention that TfL would procure a new fleet of 4-car EMUs ( Class 710) for use on both this route and the inner-suburban routes from Liverpool Street, taken over by London Overground from 2015.

Electrification was completed in February 2018 (later than the original target of June 2017) and as of June 2018 the Class 172 units were set to be replaced by Class 710 EMUs from November 2018, although this did not happen as planned. They were temporarily replaced by Class 378s redeployed from other parts of the London Overground network and moved to West Midlands Trains in March 2019. By May 2019, Class 710s started to be introduced into service.

Chiltern Railways

Chiltern Railways obtained four two-car trains in the same order as that of London Overground to supplement the Class 168 on its routes from London Marylebone, originally due to be delivered from late 2010. They did not have the tripcock safety system installed—unlike the rest of the Chiltern Railways fleet—as the design of the bogie being used (based on the B5005 found on Class 220 ''Voyager'' and Class 222 ''Meridian'' trains) meant there was no place for the brackets to be mounted. Thus, they were not able to operate on the Aylesbury via Amersham line whilst the current signalling system was in place unless running in multiple with other units on both the front and rear ends, which were fitted with a tripcock.

In 2021, all of Chiltern Railways Class 172s were leased to West Midlands Trains for use with their existing Class 172 fleet pending the delivery of Class 196 "Civity" trains."CHILTERN ‘172s’ MOVE TO WEST MIDLANDS"
''www.modernrailways.com''. 20 May 2021. Retrieved 30 January 2022. It was later announced that the Class 172/1 fleet will not be returning to Chiltern once the Class 196s enter service with WMT.

Introduction into service

In late 2007 and early 2008, orders were placed with Bombardier by two rolling-stock leasing companies to purchase a number of Class 172 ''Turbostar'' trains. In December 2007, Porterbrook ordered 15 three-car and 12 two-car trains for London Midland for delivery in 2010. In January 2008, Angel Trains, on behalf of London Overground and Chiltern Railways, ordered 12 two-car trains for delivery, which would have been delivered during 2009. But difficulties over deliveries by Bombardier's suppliers led to delays in filling the Class 377 and 378 ''Electrostar'' orders, with subsequent knock-on delays for building the Class 172 sets. Work began at the end of 2009 after the freeing-up of one of Bombardier's production lines following completion of the Class 377 order for First Capital Connect.

Eight 172/0 units were built for London Overground. Testing of the first batch of new units, the 172/0 sets for London Overground, commenced in March 2010 on the Old Dalby Test Track. All units were subsequently delivered to Willesden Train Maintenance Depot (TMD).

All eight 172/0 units entered service for London Overground. These were originally restricted to a top speed of as opposed to their intended design speed of , as it was thought there was a fault with the exhaust system requiring modifications to the original design and the already procured units. It was expected that units for London Midland and Chiltern would be delayed by a further 6–12 months. However, it transpired that the exhaust emission testing had been flawed and that there were no major problems with the units or the original design. Production therefore continued as planned with a slight delay.

The four Chiltern Railways units entered service during summer 2011 and left for West Midlands Railway in spring 2021.

Further potential orders

In 2008, First Great Western

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