British Rail Class 91

The origins of the Class 91 are closely associated with the East Coast Main Line (ECML) that it has been primarily operated upon. During the 1950s, British Rail had considered electrification of the ECML to be of equal importance to the West Coast Main Line (WCML), but various political factors led to the envisioned electrification programme being delayed for decades; as an alternative, high-speed diesel traction, including the Deltic and InterCity 125, was introduced upon the route during the 1960s and 1970s.[5] During the 1970s, a working group of British Rail and Department for Transport officials determined that, out of all options for further electrification, the ECML represented the best value by far. Its in-house forecasts determined that increases in revenue and considerable reductions in energy and maintenance costs would occur by electrifying the line.[6]

Accordingly, between 1976 and 1991, the ECML was electrified with 25 kV AC overhead lines. The electrification was installed in two phases: The first phase between London (King's Cross) and Hitchin (including the Hertford Loop Line) was carried out between 1976 and 1978 as the Great Northern Suburban Electrification Project, using Mk.3A equipment,[7] covering 30 miles in total.[6][5] In 1984, the second phase commenced to electrify the Northern section to Edinburgh and Leeds. During the late 1980s, the programme was claimed to be the longest construction site in the world, spanning more than 250 miles (400 km).[6]

During 1989, the InterCity 225 was officially introduced to revenue service.[8][9] That same year, the ECML had been energised through to York;[6] two years later, electrification had reached Edinburgh, allowing electric services to begin on 8 July 1991, eight weeks later than scheduled. The ECML electrification programme was completed at a cost of £344.4 million (at 1983 prices), a minor overrun against its authorised expenditure of £331.9 million. 40 per cent of the total cost was on new traction and rolling stock and 60 per cent for the electrification of the line.[6]

The electrification of the ECML necessitated the procurement of new high speed electric traction. The options and requirements for this trainset were hotly deliberated for a number of years. On 7 June 1978, the electric-powered prototype Advanced Passenger Train (APT) was unveiled; it was at one point intended for the APT to be the next major intercity express train.[10] However, due to various factors including technical issues, the APT programme was curtailed during the summer of 1989. Shortly thereafter, two alternative options were explored, an electrified version of the InterCity 125 (known as the HST-E), and the Class 89 mixed-traffic locomotive; these were both intended to a peak service speed of 125mph.[11]

Some officials within British Rail pushed for more demanding requirements for the future Intercity trainset; reportedly, BR's Director of Mechanical and Electrical Engineering (M&EE) was a strong proponent for increasing the top speed to 140mph.[11] To facilitate this, tilting train technologies developed for the APT were explored. While BR's board had approved the ordering of a single Class 89 as a prototype, the Strategy Committee queried why the type had been favoured over a proposed 80-tonne Bo-Bo locomotive.[11] While the Class 89 was thought to be a low-risk option for multi-purpose traction, it offered little advantage over the existing Class 87 in terms of speed. At the time, the 1950s era Class 81 and Class 85 electric locomotives were nearing the end of their viable service lives and were quite unreliable, but their withdrawal had effectively ruled out by a national shortage of newer electric traction, in part caused by the APT's cancellation.[11]

A key advantage of the InterCity 225 concept over a Class 89-hauled consist was the lower weight of the former, resulting in less slippage and greater acceleration over the latter.[11] Appraisals also determined that the Class 89 was comparatively inferior in financial terms, in part due to the InterCity 225's prospective compatibility with WCML traction, reducing its development costs. A further cost-saving measure was the decision to base the InterCity 225's technologies on the APT, BR reportedly stated that it had derived 90% of the former's engineering from the latter.[11] Thus, the study group recommended that the InterCity 225 be pursued as the preferred option, while the Class 89 and HST-E initiatives serve as back-ups. Despite this, the HST-E effort was promptly aborted, while Brush Traction decided to de-prioritise work on the Class 89 after learning that it was unlikely to lead to volume production.[11]

By spring 1984, favour was being given towards the adoption of a tilting carriage, tentatively designated as the Mk 4; this was viewed as superior to the existing Mk 3 and enabled a single design to be shared between the ECML and WCML.[11] At one point, it was envisaged that the InterCity 225 would be extremely ubiquitous, even potentially having the capability built into it to operate over the southern third-rail network and within the Channel Tunnel; by mid 1984, such fanciful ideas were curtailed. Furthermore, it was decided to reduce the freight haulage capabilities of the InterCity 225, as traction for this sector was instead intended to be served via other platforms.[11] The emergence of the Class 90, derived from the existing Class 87, somewhat reduced the pressure for the InterCity 225, reducing the prospective numbers to be built of the latter. Without tilting carriages, it had little speed advantage over the Class 90 on the WCML.[11]

It was decided to hold a competitive tender for the InterCity 225 programme; this measure was aimed at avoiding the difficulties experienced with the APT programme.[11] A pre-qualification document was formalised, in which various requirements for the type were laid out; these included the need to perform mixed-traffic duties (day and night passenger, parcel and mail, and overnight heavy freight services), the haulage of both tilting and conventional rolling stock, a top speed of 225 km/h, a maximum cant deficiency of 9° without the provision of tilt equipment, and that the maximum unsprung mass could not exceed 1.8 tonnes. Furthermore, BR stated its readiness to sub-contract with the successful bidder for the supply of technical information, advice and testing.[11] The prequalification document was issued to BREL, Brush Traction and the General Electric Company (GEC), as well as the French firm Alsthom and Germany's Krauss Maffei. The inclusion of foreign manufacturers was in part due to the limited domestic experience with trainsets capable of such high top speeds.[11] A total of three companies, ASEA, Brush Traction and GEC, submitted tenders for the design and construction of the Class 91 locomotive.[12]

On 14 February 1985, the BR board approved the substitution of the Class 91 for Class 89 for the ECML programme.[11] The tendering process was relatively complex, but a decisive move appeared to have been GEC's offer of a sub-contracting arrangement to BREL for the construction of the locomotive's mechanical elements. It would be GEC's submission that would be selected as the winner; after which a contract for the construction of 31 Class 91 locomotives, along with an option for 25 more for the WCML, was awarded during February 1986.[6][11] Shortly thereafter, BREL established a production line for the type at its Crewe Works.[11]

The Class 91 entered service with InterCity on the East Coast Main Line (ECML) in 1989.[13] In service, as a part of the InterCity 225 sets, it was used alongside other rolling stock, including Class 90 locomotives and Class 317 electric multiple units. The displaced diesel trains were reallocated predominantly to the Midland Main Line.[6] The InterCity 225's introduction correlated with a significant increase in passenger numbers using the ECML within two years; one station recorded a 58 per cent increase in passengers.[6]

In the early 1990s, after the cancellation of InterCity 250, British Rail examined the option of ordering a further set of ten Class 91s to operate on the West Coast Main Line with UK Treasury support, however the business case for these failed to prove sufficiently worthwhile.[14] and led to the electric Networker Classes 365, 465 and 466 EMU Networker stock's procurement being taken forward.

91115 running blunt-end first at London King's Cross

The asymmetric body style is streamlined at one end to allow high-speed operation, with the fixed sets of Mark 4 coaches in normal push-pull passenger operation. An additional requirement of the design was that they could operate as normal locomotives. This led to a second cab being incorporated into the unstreamlined 'blunt end'. Operating with the blunt end first limits the maximum speed of the locomotive to 110 mph (180 km/h).

As a consequence of the privatisation of British Rail, the Class 91 fleet was entirely acquired by the Eversholt Rail Group, which had leased it to various train operating companies. Between 2000 and 2003, the whole fleet underwent a refit (Project Delta) to improve reliability. The Class 91 units were refurbished at Bombardier Transportation at its Doncaster Works. This has resulted in the renumbering of the fleet from 910xx to 911xx. During this time, GNER hired in Class 90 locomotives to provide cover.[15]

A Class 91, 91010 (now 91110), holds the British locomotive speed record at 161.7 mph (260.2 km/h), set on 17 September 1989,[16] just south of Little Bytham on a test run down Stoke Bank with the DVT leading. Although Class 370s, Class 373s and Class 374s have run faster, all are EMUs which means that the Electra is officially the fastest locomotive in Britain. Another loco (91031, now 91131), hauling five Mk4s and a DVT on a test run, ran between London King's Cross and Edinburgh Waverley in 3 hours, 29 minutes and 30 seconds on 26 September 1991. This is still the current record. The set covered the route in an average speed of 112.5 mph (181.1 km/h) and reached the full 140 mph (225 km/h) several times during the run.

The Class 91 was designed to achieve a peak service speed of 140 mph (225 km/h); the upper range of its high speed capabilities facilitated a 3hr 29mins non-stop run between London and Edinburgh on 26 September 1991.[6] However, British regulations have since required in-cab signalling on any train running at speeds above 125 mph (201 km/h) preventing such speeds from being legally attained in regular service.[17] Thus, except on High Speed 1, which is equipped with cab signalling, British signalling does not allow any train, including the InterCity 225, to exceed 125 mph (201 km/h) in regular service, due to the impracticality of correctly observing lineside signals at high speed.

The fleet, which was previously operated by InterCity and then GNER, National Express East Coast, East Coast and Virgin Trains East Coast, is currently run by London North Eastern Railway.

In July 2019, 91108 was the first of the class to be withdrawn.[25] Following the withdrawal of the InterCity 125 fleet in December 2019, it was previously thought that the InterCity 225 fleet would be fully withdrawn by June 2020.[26] However, LNER announced on 29 January 2020 that they would be retaining a limited number of the InterCity 225 fleet to deliver all of the benefits of their December 2021 timetable.[27] LNER later confirmed that they would be keeping 10 sets in service.[28]

In September 2020, Eversholt Rail Group and London North Eastern Railway extended their lease to 10 by 2023. In addition, there are options to make it operational until 2024. It will be overhauled at the Wabtec Doncaster plant.[29][30]

At the end of service on 15 January 2021, the remaining serviceable InterCity 225 sets went into storage and are currently not in service. The sets are planned to return to service in summer 2021 after engineering works at King's Cross station have been completed as part of the East Coast Upgrade.[31]

Europhoenix purchased 91117 and 91120 in September 2019. They were repainted at Bounds Green TMD before moving to UK Rail Leasing's Leicester depot. They are to be re-geared for freight operation in Europe.[32]

Rail Operations Group have taken a pair of Class 91s for use in testing of the newly electrified Midland Main Line prior to the introduction of regular electric services between Bedford and Corby.[33] The company has also expressed interest in using the Class 91s on high speed logistics trains.[34]

Grand Union is proposing to operate InterCity 225s on London Paddington to Cardiff Central and London Euston to Stirling services.[35][36]

• P.J. Donnison; G.R. West (25–28 September 1989), Institution of Electrical Engineers (ed.), "The design and development of the class 91 locomotive", IEE Conference Publication (312): 294–298, ISBN 978-0-85296-384-5
• P.C. Bennett (25–28 September 1989), Institution of Electrical Engineers (ed.), "Aspects of the design, construction and testing of BRB's Class 90 and 91 locomotive transformers", IEE Conference Publication (312): 279–283, ISBN 978-0-85296-384-5
• R. Dettmer (12 May 1998), "The Class 91 locomotive. Learning from the APT", IEE Review, 34 (5): 188–189, doi:10.1049/ir:19880072, ISSN 0953-5683
• Broom, M. L.; Smart, G. W. (1990). "The design, manufacture and assembly of the wheelset for the British Rail Class 91, 25 kV, 225 km/h locomotive". Proceedings of the Institution of Mechanical Engineers, Part F: Journal of Rail and Rapid Transit. 204 (26): 141. doi:10.1243/PIME_PROC_1990_204_200_02. S2CID 111232510.