British Rail Class 166

British Rail Class 166
Networker Turbo Express

Original Interior of 166208 at Reading station
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
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. 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:

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:

One driving vehicle of 166209 had serious fire damage, as a result of the Betchworth train fire.[4] During this period, the centre coach 58609 intercepted the middle of 165128 and the unaffected driving vehicle was out of service in Reading Train Care Depot. However, as of 21st May 2016, it was put back in service following 6 months of repairs.

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.[5][6]

Class 166 units were some of the first trains in Britain to be 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.


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 and therefore carried NSE blue, red and white livery with Turbo Express branding between the two first class windows of the DMCL carriages.

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.

A rail user's group has suggested that Class 165 Turbo and the express variant, Class 166 Turbo Express will work services on the Cardiff Central to Portsmouth Harbour route after the Thames line cascade, subject to line clearance.[7] However, a Network Rail document released in 2011 cast doubts on whether this would actually happen after revealing the gauge between Cardiff and Portsmouth is currently not suitable for Class 166s.[8]

Following privatisation, the units passed to the Thames Trains franchise, who introduced a new blue, white and green livery. There were two variants of this livery; the Class 166 units had the 'express' variant.

In April 2004, operation of the Thames Trains franchise passed to the First Great Western Link, and subsequently to First Great Western. The livery remained the same initially, but FGW Link branding was applied over the obsolete Thames Trains logo.

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 to be used entirely for Thames Valley services.[9]

London and Thames Valley Refresh

166217 in Thames Trains livery with First Great Western Link branding. FGWL never repainted the units before being subsumed into the Greater Western franchise as part of First Great Western.

Towards the end of January 2010, First Great Western announced an £8,000,000 refresh programme to their fleet of Class 166 Turbo DMU trains.[10] 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.

2014/15 Refresh

Since late 2014, First Great Western have started another set of refreshes to the Class 166 fleet. They are progressively being fitted with LED head/tail lights, a new, dark green GWR livery, new toilets which are more accessible than the old toilets, new door buttons which are significantly easier to push than the original buttons, and new door buzzers. All units have now received the refresh. Unit 166204 was named in honour of Twyford Stationmaster Norman Topsom MBE who retired in November 2015, 166205 received a GWR interior and 166201-203, 166207, 166209, 166211, 166215 and 166221 were painted in an all over blue livery.

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

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


  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".
  3. "Passengers to benefit from additional carriages" (Press release). First Great Western. 23 February 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. "London to the Cotswolds - General Information". First Great Western Passengers' Forum. 6 February 2008. Retrieved 9 June 2011.
  7. Network RUS: Passenger Rolling Stock - Network Rail. September 2011.
  8. "Return of Adelantes to First Great Western confirmed". 2011-11-23. Retrieved 2011-11-23.
  9. "Train operator gives Thames Valley Trains an £8million makeover" (Press release). First Great Western. 25 January 2010. Retrieved 9 June 2011.
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