British Rail Class 166

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British Rail Class 166
Networker Turbo Express
166208 in GWR by Chris Warman.jpg
166205 Standard Class Interior.jpg
The refurbished interior of Standard Class
In service 1992 - Present
Manufacturer ABB York
Family name Networker
Constructed 1992 - 1993
Number built 21 trainsets
Formation 3 cars per trainset
Fleet numbers 166201 - 166221
Operator(s) Great Western Railway
Line(s) served
Car body construction Welded aluminium
Maximum speed 90 mph (145 km/h)
Prime mover(s) One per car, Perkins 2006-TWH Diesel
Power output 350 hp (261 kW)
Transmission Voith Hydraulic T211r
2 axles driven per car
Safety system(s) AWS, TPWS
Coupling system BSI[1]
Track gauge 1,435 mm (4 ft 8 12 in) standard gauge

The British Rail Class 166 Turbo Express is a fleet of diesel multiple units (DMUs), originally specified by and built for British Rail, the then United Kingdom state owned railway operator. They were built by ABB at York Works between 1992 and 1993.[2] The trains were designed as a faster, air conditioned variant of the Class 165 Turbo, intended for longer distance services, and, like the 165s, belong to the Networker family of trains. They were originally known as Networker Turbos to distinguish them from the electrically propelled members of that family.

The class is still in service, and is extensively operated by Great Western Railway on its services out of London Paddington station, and since July 2017 are also operated on services on the Severn Beach Line. The trains, along with that operator's Class 165 trains, are often known as Thames Turbos.


These units are a modification of the Class 165 design. They have a top speed of 90 mph (145 km/h) (suitable for mainline use), are carpeted throughout and have air-conditioning. Externally, the class 166 can be distinguished from a Class 165 by opening hoppers on every other window. Until late 2013 the presence of first class at each end was another distinguishing feature.

Other differences over a 165 are as follows:

  • Air conditioning
  • Two toilets (a 165 only has one toilet per unit)
  • Tables in first class and in one third of the middle carriage
  • Dedicated cycle/luggage storage in the middle carriage
  • Different interior panelling between the door and seating areas

Twenty-one 3-car units were built, numbered 166201-221. Each unit was formed of two outer driving motors, and an intermediate motor. The technical description of the formation is DMCO+MSO+DMSL. Individual carriages are numbered as follows:

  • 58101-58121 - DMCO
  • 58601-58621 - MSO
  • 58122-58142 - DMSL changed from DMCO in 2013[3]

The units were built to replace elderly Class 117, Class 119 and Class 121 DMUs, and locomotive-hauled trains on services from London Paddington along the Great Western Main Line.

Six cars were added to the original order in 1991 after Network SouthEast acquired some of the Cotswold Line services from Regional Railways to allow Class 158 units to be converted to Class 159s for the West of England services.[4][5]

Class 166 units are designed for Driver Only Operation. In cases where a Guard is required they must carry out their door operation duties via a bell system to signal the Drivers to close doors and start the train. This requires the Guard to return to a vacant cab at each station to carry out these duties; this practice can be observed on Great Western Railway services on the Cotswold Line and North Downs Line.[citation needed]


166220 arrives at Oxford with a service to London Paddington.

When built, these units were operated by the Thames Line and North Downs Line subdivisions of Network SouthEast.

Their main destinations included fast-trains to Reading, Newbury and Oxford, with some services continuing beyond Oxford to Banbury and Stratford-upon-Avon, or along the Cotswold Line to Evesham, Worcester, Great Malvern and Hereford. Units are also used on the Reading to Gatwick Airport services along the North Downs Line. Many services operated by the 166 were branded as Turbo Express in the timetables.

Following privatisation, the units passed to the Thames Trains franchise. In April 2004, operation of the Thames Trains franchise passed to the First Great Western Link, and subsequently to First Great Western.

In 2012, First Great Western took delivery of five Class 180 Adelante units for Cotswold Line services, and three-car Class 150 Sprinter units for Reading to Basingstoke Line services, allowing Class 165 and 166 units to be used entirely for Thames Valley services.[6]

Great Western Railway unit 166212 at Clifton Down on the Severn Beach Line in Bristol, July 2017

From July 2017, a number of Turbos were transferred to the Severn Beach Line to provide extra capacity during busy services.[7]

The Class 166 units are expected to enter service on Bristol Parkway to Weston-super-Mare services on 23 October 2017.[8]

London and Thames Valley Refresh[edit]

166217 in Thames Trains livery with First Great Western Link branding.

Towards the end of January 2010, First Great Western announced an £8 million refresh programme to their fleet of Class 166 Turbo DMU trains.[9] The carpets & seats were retrimmed, interiors repainted, Passenger Information Displays replaced with a GPS based system and toilets upgraded. The refresh work was carried out at Reading Depot. All 151 vehicles have now been refurbished.

In late 2014, another set of refreshes to the Class 166 was started. This included the fitting of LED head/tail lights, new toilets which are more accessible than the old toilets, new door buzzers & new door buttons of the standard design with a round button on a yellow ring. All units have now received the refresh. Unit 166204 was named in honour of Twyford station master Norman Topsom MBE who retired in November 2015. The changes made during the 2010 refresh remain in place, however the units will all be receiving new 2+2 seating, for use on longer distance services such as Bristol to Weymouth once the fleet are cascaded to the Bristol area.

Fleet details[edit]

Class Operator No. Built Year Built Cars per Set Unit nos.
Class 166/2 Great Western Railway 21 1992–1993 3 166201 - 166221

Liveries and interiors[edit]

GWR Class 166 Turbo.png


  1. ^ "Mechanical And Electrical Coupling Index". Rail Safety and Standards Board. Archived from the original on 21 December 2013. Retrieved 20 December 2010. 
  2. ^ "First Great Western Info". Archived from the original on 2012-12-09. 
  3. ^ "Passengers to benefit from additional carriages" (Press release). First Great Western. 23 February 2015. Archived from the original on 25 March 2015. Retrieved 3 April 2015. 
  4. ^ "Turbo-trains". Hansard. 192: 278W. 6 June 1991. Retrieved 9 June 2011. 
  5. ^ "Class 159". Southern E-Group. Retrieved 9 June 2011. 
  6. ^ "Return of Adelantes to First Great Western confirmed". Retrieved 23 November 2011. 
  7. ^ "train maintenance". Great Western Railway. Retrieved 9 June 2017. 
  8. ^
  9. ^ "Train operator gives Thames Valley Trains an £8million makeover" (Press release). First Great Western. 25 January 2010. Archived from the original on 11 June 2011. Retrieved 9 June 2011.