Background The origins of the Class 91 are closely associated with the
East Coast Main Line (ECML) on which it has been primarily operated. 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, the
Deltic and then the
InterCity 125, was introduced upon the route during the 1960s and 1970s. During the 1970s, a working group of British Rail and
Department of 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. Accordingly, between 1976 and 1991, the ECML was electrified with
overhead lines. The electrification was installed in two phases: The first phase between London (King's Cross) and (including the
Hertford Loop Line) was carried out between 1976 and 1978 as the
Great Northern Suburban Electrification Project, using Mk. 3A equipment, covering in total. That same year, the ECML had been energised through to
York; However, due to various factors including technical issues, the APT programme was curtailed during the summer of 1983. Shortly thereafter, two alternative options were explored, an electrified version of the
InterCity 125 (known as the
HST-E), and the mixed-traffic locomotive; these were both intended to a peak service speed of . 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 . in 1990 On 14 February 1985, the BR board approved the substitution of the Class 91 for Class 89 for the ECML programme. and led to the electric
Networker Classes
365,
465 and
466 EMU Networker stock's procurement being taken forward. The locomotive body is asymmetric; streamlined at the 'front' (Number 1) end , but left 'blunt' at the Number 2 end so as to visually blend with the fixed sets of Mark 4 coaches in normal push-pull passenger service. Because of a design requirement that the class be able to function as normal locomotives if so required, a full driver's cab is also provided at the Number 2 endbut the locomotive's maximum speed is reduced to when this cab is at the front of a train. During the
privatisation of British Rail ownership of the Class 91 fleet passed to
Eversholt Rail Group, which in turn leased the fleet to its various operators. Eversholt put all 31 locomotives through a £30million heavy overhaul and refit process () between 2000 and 2003, seeking to improve the fleet's reliability.
Rail Magazine described it in March 2001 as being necessary because "eight out of ten failures on Class 91s were caused by the sub-standard electrics", and further noted that problems with
relays in particular were the "third-biggest" cause of failures. In November 2012, number 91114 had a second pantograph added as a pilot project conducted jointly by Eversholt,
East Coast, DB ESG,
Wabtec, and
Brecknell Willis. The new design uses the same mounting positions as a conventional pantograph but pairs two pantograph arms in an opposing configuration. If there is an ADD (Automatic Dropping Device) activation or the pantograph becomes detached, the train can keep going, so the system provides redundancy in the event of a pantograph/OLE failure.
Speed records Locomotive 91010 (now 91110) holds the British speed record for electric locomotives, reaching while on a test run down the East Coast Main Line's
Stoke Bank on 17 September 1989. Locomotive 91012 (now 91112) holds the separate record for the fastest non-stop journey between
London King's Cross and ; 3hours29minutes on 26 September 1991, running within the speed limit but hauling a shortened set of only five coaches plus DVT. The time converts to an average speed of . Despite these successes, however, Class 91 locomotives have never used their 140mph top speed in regular service, because testing conducted by British Rail in 1988 established that drivers could not interpret and act upon line-side signal aspects with sufficient consistency and accuracy when driving at speeds exceeding . Regulations throughout Britain were subsequently amended to require the use of
in-cab signalling whenever running service trains at speeds above 125mph, an option that BR were unwilling to pursue at the time. == Fleet ==