InterCity 125
The InterCity 125 or High Speed Train is a diesel-powered high-speed passenger train built by British Rail Engineering Limited between 1975 and 1982. A total of 95 sets were produced, each comprising two Class 43 power cars, one at each end, and a rake of seven or eight Mark 3 coaches. The name is derived from its top operational speed of. At times, the sets have been classified as British Rail Classes 253, 254 and 255.
British Rail initially developed the HST as an interim measure in the early 1970s, as delays and cost concerns began to threaten their primary high-speed train project, the Advanced Passenger Train. The HSTs are now widely considered to be among the most successful trains to have operated on the British railway network, both in terms of their initial impact and their longevity: their introduction into service between 1976 and 1982 resulted in significantly reduced journey times, and large increases in patronage on the routes on which they were operated. The trains proved to be a reliable workhorse, remaining in front-line service for decades. The first withdrawals began in 2017, 41years after they were introduced., InterCity 125s remain in service with ScotRail and Network Rail.
The design became the basis for an Australian variant, the Express Passenger Train, which entered service in New South Wales in 1982.
Background
In the late 1950s and early 1960s, the British Transport Commission was modernising its rail network. It wanted to increase intercity speeds so that railways could compete more effectively with motorways. The governments of the time were unwilling to fund dedicated high speed rail infrastructure, as happened in other countries, and so the BTC instead focused on developing new trains which could operate at higher speed using existing infrastructure. A team of engineers was assembled at the Railway Technical Centre in Derby in the early 1960s, to design and develop an Advanced Passenger Train capable of at least incorporating many features not previously seen on British railways—such as tilting to allow higher speeds on curves.The APT project suffered repeated delays and in 1970, the British Railways Board decided it would not be sufficiently developed to enter public service until well into the next decade, so a stopgap solution would be needed to reduce journey times in order to compete effectively with other modes of transport. At the instigation of Terry Miller, Chief Engineer, the BRB authorised the development of a high-speed diesel train using tried and tested conventional technology for short-term use, until the APT was able to take over. An operational prototype was to be built by 1972.
Development
Concept and design
The high-speed diesel train, which became the HST or InterCity 125, was formed of a rake of Mark 3 passenger coaches between two streamlined power cars, one at each end. Each power car was fitted with a Paxman Valenta diesel engine which could produce. This engine was chosen due to its light weight, and subsequent high power-to-weight ratio. The decision to use two power cars was taken early in the project as design engineers calculated that the train would need to sustain 125mph on the routes for which it was designed, and it was established that no "off-the-shelf" diesel engine was capable of producing such power.British Rail had used a similar idea of a train with integral power cars at each end a decade earlier, with their Blue Pullman sets; although these trains were not ultimately commercially successful, they established the validity of the idea, and are often seen as forerunners of the HSTs. The concept had several advantages; firstly, a power car at each end allowed the train to be driven from either end in push–pull formation with the power cars linked by electronic control systems, and therefore reverse direction without the need for a locomotive to be run around at terminus stations, secondly, the train could run with only one power car operational, though at reduced speed, therefore allowing a journey to continue in the event of a breakdown, and thirdly, it avoided the underfloor diesel engines found in diesel multiple units, therefore avoiding noise and vibration for passengers. Another factor was that two locomotives operating in push–pull formation, would cause less wear on the rails than a single locomotive. One of the design requirements for the HST was that it should exert no more force on the track at 125mph, than a Class 55 'Deltic' locomotive at 100mph, and each power car of the HST weighed a modest 70tons which allowed it to meet this requirement.
One of the key design requirements for the HSTs was that they should be able to run at 125mph on existing infrastructure. In order to achieve this, they had to be able to come to a stop from 125mph within existing signal spacings, which required a high performance braking system to be developed. This was achieved by a high performance disc brake system, in place of the clasp brakes used on traditional stock.
Prototype
To prove the concept, British Rail produced a prototype. The framework of the new locomotive, classified British Rail Class 41, was built at Crewe Works and transferred to Derby Litchurch Lane Works for completion. The design incorporated a driving desk around the centrally seated driver, a sound-proofed door between the cab and the engine room, and, unusually, no side windows. The prototype was the first diesel locomotive in British railway history to use AC alternators in place of a DC generator, with the output converted to DC when used for traction.The prototype train of seven coaches and two locomotives was completed in August 1972 and in the autumn was running trials on the main line. The following year, high-speed testing was undertaken on the "racing stretch" of the East Coast Main Line between York and Darlington. The set was reduced to two power cars and five trailers, and there was a concerted attempt to see how fast the train would go. On 6 June 1973, was reached, which was bettered as the days passed. On 12 June, a world diesel speed record of was achieved, and the drivers believed that 150 mph was possible, but the BRB issued instructions for the high speed tests to cease. It was believed at the time that this was because the BRB wanted to promote the APT as the future of high speed rail travel in the UK.
The fixed-formation concept was proven in trial running between 1973 and 1976, and British Rail went on to build 95 sets of production HSTs to transform InterCity services.
Production versions
Manufacturing of the production power car sets began in 1974 at the Crewe Works, with the Mark 3 coaches being manufactured at the Derby Litchurch Lane Works. The first production power car, numbered 43002, was delivered in late 1975. The production versions were mechanically very similar to the prototype, but differed considerably in appearance: the streamlined wedge-shaped front end lacked conventional buffers, and the drawgear was hidden under a cowling. The single cab front window was much wider than the prototype's, and side windows were included. Unlike the prototype, no driving position was included at the inner end, as the power cars were originally intended to operate in fixed formation.The train's appearance is the work of British industrial designer Kenneth Grange who was approached by British Rail to design the livery, but under his own impetus, and without telling anyone, decided to redesign the body. He worked with an aerodynamic engineer, and they built and tested a model in a wind tunnel. "It really was rather quite brutal, rather clumsy. I thought, 'Oh I'd like to get my hands on that', although the brief was nothing to do with the shape, absolutely not at all." He presented the new design to British Rail and persuaded them to adopt it. In 2016 GWR renamed 43002 "Sir Kenneth Grange" in his honour, at the same time returning it to its original blue and yellow paint scheme. After being withdrawn from GWR service, 43002 was acquired by the National Collection in November 2019 and was displayed at the National Railway Museum in York.
The redesigned front end also had the advantage of easing union acceptance of the train: the railway union ASLEF had objected to the prototype's lack of space for a secondman to sit alongside the driver, and had refused to operate the prototype in public service. The cab on the production version was wide enough to accommodate two people, and so was able to overcome these objections.
An InterCity 125 consists of two Class 43 diesel-electric power cars, each powered originally by 2,250 bhp Paxman Valenta engines, and a set of six to nine Mark 3 coaches.
Key features of the design are the high power-to-weight ratio of the locomotives, which were built for high-speed passenger travel, improved crashworthiness over previous models, and bi-directional running avoiding the need for the locomotive to run around at terminating stations. Until the HST's introduction, the speed of British diesel-powered trains was limited to. The HST allowed a 25% increase in service speeds along many of the lines on which they operated.
Lighter axle loading allowed the trains to travel faster than conventional services along lines not suited to full-speed running, such as Edinburgh to Aberdeen. Coupled with superior acceleration over older locomotives, this allowed substantial cuts in journey times. The increased speed and rapid acceleration and deceleration of the HST made it ideal for passenger use.
British Rail service
Introduction into service
Deliveries continued in 1976, and on 4 October a partial service of HSTs running at began on the Western Region, from, on the Great Western and South Wales Main Lines. The radical update of the standard BR livery on the power cars was complemented by the 'Inter-City 125' branding, which also appeared on timetables and promotional literature. By the start of the summer timetable in May 1977, the full complement of 27 Class 253 sets was in service on the Western Region, replacing locomotive-hauled trains on the Bristol and South Wales routes. Passenger numbers rapidly increased due to the speed and frequency of the services. The displacement by HSTs of Class 50 locomotives to slower services effectively finished off the last Class 52 diesel-hydraulics by early 1977.The production of Class 254 continued through 1977 for East Coast Main Line services. The HSTs allocated to the ECML had eight coaches instead of seven on the Western Region, and British Rail had originally planned to fit uprated Valenta engines to the longer HSTs, but this was not carried out, as it was found that the engine's coolant system would struggle to deal with the extra heat produced by a higher powered engine. The first 125mph East Coast HST services were introduced for the summer timetable in May 1978, with HSTs taking over Flying Scotsman and other services. The previous generation of Class 55 'Deltic' locomotives were relegated to secondary duties, before being withdrawn entirely in late 1981. A full HST timetable for the ECML was due to be introduced in May 1979, but was delayed until late August due to the Penmanshiel Tunnel collapse. The HSTs reduced the London-Edinburgh journey time by up to an hour.
In 1979, HST services began in South West England, to destinations such as Exeter, and, and in 1981 they were introduced to the Cross Country Route via. In 1982 HSTs were introduced to Midland Main Line services from London St Pancras: Although the HSTs were mostly limited to a top speed of on those routes, their increased acceleration still reduced journey times.
Ninety-five HST sets, including 197 Class 43 powercars, were built between 1976 and 1982. More Mark 3 trailer cars were built in the 1980s for the Western Region Class 253s, making them eight-car rakes in common with East Coast and Midland Main Line services. During the 1990s only the Cross-Country sets remained as seven-car rakes, with just one first-class coach.
One of the main selling points of the new HST services were the increase in speed and comfort without any increase in fares. The HST brought considerable improvements in service, and British Rail began active marketing to support the train's introduction. The InterCity service was a great success for British Rail.