InterCity 125

The InterCity 125 (originally Inter-City 125New train speeds into service
. BBC News, 1976-10-04; reproduced in the BBC "On This Day" website, accessed on 2019-05-15.) or High Speed Train (HST) is a diesel-powered high-speed passenger train built by British Rail Engineering Limited between 1975 and 1982. Each set is made up of two Class 43 power cars, one at each end, and a rake of Mark 3 carriages. The name is derived from its top operational speed of . Initially, the sets were classified as Classes 253 and 254.

The HSTs were originally developed by British Rail (BR) in the early 1970s to be used as a stopgap, whilst it developed the tilting Advanced Passenger Train (APT). In the event, the APT project was a failure, and the HSTs became a big success. The HSTs, or InterCity 125s are now widely considered as 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 have proved to be a reliable workhorse, remaining in front-line service for decades. The first withdrawals began in 2017, 41 years after they were first introduced, to be replaced with more modern trains.

As of August 2021, InterCity 125s remain in service with ScotRail, CrossCountry, Great Western Railway, and Network Rail.

The design became the basis for an Australian variant, the XPT, which entered service in New South Wales in 1982.

Background

In the late 1950s and early 1960s, the British Transport Commission (BTC) was modernising its rail network. It wanted to increase intercity speeds so that railways could compete more effectively with motorways. The government was unwilling to fund new railways and the BTC focused on increasing line speeds by developing new trains and modifications to the 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 (APT) 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 (BRB) decided it was not sufficiently developed to modernise the railways in the short term and at the instigation of Terry Miller, Chief Engineer (Traction & Rolling Stock), the BRB authorised the development of a high-speed diesel train using 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 2,250 horsepower. 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 125 miles per hour on the routes for which it was designed (the Great Western Main Line, East Coast Main Line, Midland Main Line, and the Cross Country Route), 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 125 mph, than a Class 55 'Deltic' locomotive at 100 mph, and each power car of the HST weighed a modest 70 tons 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 125 mph on existing infrastructure. In order to achieve this, they had to be able to come to a stop from 125 mph 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, 131 mph 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. 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 (1,678 kW) Paxman Valenta engines (they have since been fitted with different 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 (1678 kW per ~70-tonne loco), 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 (253001–253027) 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 (ECML) services. The HSTs allocated to the ECML had eight carriages 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 125 mph 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 : 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 carriage.

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.

Journey time reductions

One of the main selling points of the HSTs were the reductions they could achieve in journey times, with the trains being marketed in publicity material as 'The Journey Shrinker'. In 1973 British Rail produced a promotional booklet entitled ''Speed for the Seventies'' in which they laid out the expected journey times to be achieved with HSTs compared to the then extant timings.

Most of these predictions of the journey times achievable by HSTs proved to be quite accurate, and in some cases they were underestimates. For example, the best timing achieved for London to Bath was 62 minutes, and 115 minutes was achieved for London to York.

Proposed electric version

In the early 1980s, when electrification of the East Coast Main Line was in its early planning stages, serious consideration was given to producing an electric version of the HST, which would have been known as the HST-E. This would have kept the bodyshell and most of the mechanical components of the diesel version, but the power cars would have been electric locomotives fitted with pantographs. The thinking was, that as the diesel version had been proven, it would be a straightforward way to produce a 125mph trainset. The HST-E was proposed in response to the failure of the Advanced Passenger Train (APT) project. This proposal did not proceed, and BR instead developed a new electric trainset which would become the capable InterCity 225 to work the electrified services on the ECML, which came into service in the late-1980s.

World records

The prototype InterCity 125 (power cars 43000 and 43001) set the world speed record for diesel traction at on 12 June 1973.

A HST also holds the world speed record for a diesel train carrying passengers. On 27 September 1985, a special press run for the launch of a new ''Tees-Tyne Pullman'' service from to , formed of a shortened 2+5 set, briefly touched north of . The world record for the fastest diesel-powered train, a speed of , was set by an HST on 1 November 1987, between Darlington and York with a test run for a new type of bogie for use on Mark 4 coaches on the same route. The record run was led by 43102 and trailed by 43159.

Regions and operators

South West England and South Wales

On the Western Region, InterCity 125 trains (designated class 253) were introduced on services from London to Bristol and South Wales, and extended to most daytime services from London to Devon and Cornwall. Some South Wales services were extended to , and in West Wales. Maintenance was provided at Old Oak Common and St Philip's Marsh, and Laira also carried out maintenance after services to Devon and Cornwall were introduced in 1979.

British Rail Class 47 locomotives still operated cross-country services from Cornwall and South Wales to the North-East via the Cross Country Route, and London to the Midlands/Welsh Marches. Class 43s replaced them when the third batch of power cars was delivered in 2+7 formation with two first class coaches, a buffet car, and four second class coaches between two power cars. They were later expanded to a 2+8 formation, with an extra second class carriage.

Great Western Trains was formed out of the privatisation of British Rail and operated the InterCity routes from London Paddington to the west of England. In 1998 FirstGroup