British Rail Class 172

The Class 172 is a type of diesel multiple unit (DMU) of the Turbostar family, similar to the Class 168, Class 170 and Class 171.

Technical details and variants
There will be four sub-types: The 172/0s and 172/1s will resemble the existing Turbostar trains in not having end gangways and will have a top speed of 100 mph due to their use on the high volume/short distance services, such as those on the Gospel Oak to Barking Line. The Class 172/3s used by London Midland will resemble the Class 375, Class 377 and Class 379 Electrostars by having end gangways to allow access between units. These trains will have a maximum speed of 100 mph. The Class 172 trains will be lighter than other Turbostars thanks to the addition of similar lightweight bogies to those fitted to the Class 220 Voyager trains. They also differ from earlier Turbostars in having mechanical transmission rather than hydraulic.
 * Class 172/0 - two-car units in operation with London Overground
 * Class 172/1 - two-car units to be operated by Chiltern Railways
 * Class 172/2 - two-car units to be operated by London Midland
 * Class 172/3 - three-car units to be operated by London Midland

Differences from Class 150
A Class 172 Turbostar will have fewer seats than a Class 150 Sprinter it replaces (e.g. a three-car 150/1 has 35 more seats than a three-car 172/3) 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 will be air conditioned and have no openable windows, unlike the Class 150s.

Operators
London Overground operate 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, but due to production issues and then some exhaust problems, the trains only started service in September 2010; and then at reduced capacity due to problems training staff on the units. By December, the whole fleet was in service, allowing the Class 150s to be cascaded to First Great Western and other operators. The units are leased by London Overground Rail Operations Ltd (LOROL), the London Overground concession operator, from a rolling stock leasing company rather than them being purchased directly by Transport for London. London Midland will operate a total of 27 two-car and three-car units, originally planning for them to enter service by the end of 2010 on services to and from Birmingham Snow Hill, again replacing Class 150s. The London Midland sets have end gangways which make the trains look like the Electrostar Classes 375, 377 and 379. Chiltern Railways will obtain four two-car trains in the same order as that of London Overground to supplement the current Class 165 Networker Turbos on their routes from London Marylebone, originally due to be delivered from late 2010. These trains will differ from the London Overground units with the addition of the ATP safety system, to make them compatible with the rest of the Chiltern fleet. They will not have the tripcock safety system installed&mdash;unlike the rest of the Chiltern Railways fleet&mdash;as the design of the bogie being used (based on the B5005 found on Class 220 Voyager and Class 222 Meridian trains) means there is no place for the brackets to be mounted. Thus, they will not run on the Aylesbury via Amersham line unless completely boxed in by units fitted with a tripcock to the front and rear.

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. However, difficulties encountered by Bombardier over the deliveries by its suppliers led to delays in filling the Class 377 and 378 Electrostar orders, with subsequent knock-on delays for building the Class 172 Turbostar trains. Work began at the end of 2009 after the freeing up of one of Bombardier's production lines following the completion of the Class 377 Electrostar order for First Capital Connect. Eight 172/0 units have been built for London Overground. Testing of the first batch of new units, the 172/0 sets for London Overground, commenced in March 2010, with two sets (anonymous as they did not have unit numbers on them) being tested on the Old Dalby Test Track. All units have been subsequently delivered to Willesden Train Maintenance Depot (TMD). All eight of the 172/0 units have entered service for London Overground. Units were originally restricted to a top speed of 40 mph as opposed to their intended design speed of 75 mph as it was thought there was a fault with the exhaust system requiring modifications to the original design and the already procurred units. It was expected that units for London Midland and Chiltern would be delayed by a further 6–12 months. However it has later transpired that exhaust emission testing was flawed and there are no major problems with the units or the original design, with production continuing as planned with a slight delay. Trainset number 172331, which is the first set from the 172/3 sub-class and features gangwayed-ends, began testing at the Old Dalby Test Track on 6th January 2011 and has now been delivered to London Midland's Tyseley Depot.

Further potential orders
As part of their franchise agreement, London Midland have an option to purchase an additional 26 Class 172 vehicles which could potentially allow further cascade of their existing rolling stock. In 2008, First Great Western applied to the Department for Transport to re-equip its Cardiff to Portsmouth via Bristol services with 11 new four-car DMUs which would potentially allow the existing Class 158 Express Sprinter trains to be transferred to other services. According to the West of England Partnership, these are likely to be "similar to Class 170s", suggesting that they might be Class 172 Turbostars. The Government announced in December 2008 that Bombardier, with its Turbostar design, was one of the pre-qualified bidders (along with CSR of China, CAF of Spain and Rotem of South Korea) for the first 200 DMU vehicles of its planned 1300 new carriages. These new trains were intended for use on suburban and inter-urban services operated by First Great Western, First TransPennine Express and Northern Rail. However, with the announcement of the electrification of the Great Western Main Line, the DMU order was cancelled, with the needs of the train operating companies planned to be met by transfers of existing stock. Bombardier offered the Class 172 Turbostar to NI Railways for its "New Trains Two" specification, eventually losing out to CAF and a variation of NIR's existing Class 3000.