British Rail Class 172

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.[9] 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.

Class 172s have fewer seats than the Class 150s they replaced,[8] 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 23 m (75 ft 6 in) body length, as opposed to the 20 m (65 ft 7 in) length used on previous Class 150 Sprinter DMUs - increasing capacity.

172006 at Leamington Spa in 2020. This was originally with London Overground.

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.[10] 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.[11] 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.

London Overground Class 172/0 No. 172005 at Walthamstow Queen's Road

The interior of a London Overground Class 172/0

London Overground operated eight two-car Class 172s on the Gospel Oak to Barking line, replacing the old Class 150 stock. The units were originally meant to be in service from February 2010,[12] but due to production issues and then what were thought to be exhaust problems (which proved to be a false alarm),[13] 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 and other operators. The units were leased by Angel Trains.[14]

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.[15] 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.[16]

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.[17] 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.

A pair of Chiltern Railways Class 172/1 No. 172104 and No. 172102 at London Marylebone

The interior of a Chiltern Railways Class 172/1

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.[18] 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.[19] It was later announced that the Class 172/1 fleet will not be returning to Chiltern once the Class 196s enter service with WMT.[20]

Unit 172342 is named Roger Sumner, in honour of a driver at Worcester who retired in late 2022 after almost 60 years of service. He was the last employee at West Midlands Trains to have previously worked on steam locomotives for British Rail.[30][31]