The British Rail Class 150 Sprinter is a class of diesel multiple unit passenger trains; they were developed and constructed by British Rail Engineering Limited at York Carriage Works between 1984 and 1987 for use on regional services across the UK. The type is a second-generation design, built to more modern standards and based on BR's Mark 3 body design for longer-distance services. It was developed alongside the lower-cost Pacers, which were built using bus parts, for use on short-distance services. Two prototype units were built, followed by 135 production units in two batches. Subsequently, further members of the Sprinter family were also developed and introduced to service, including the Class 155, Class 156, Class 158 and Class 159.
Background
By the beginning of the 1980s, British Rail (BR) was operating a large fleet of first-generation DMUs of various designs. While formulating its long-term strategy for this sector of its operations, BR planners recognised that there would be considerable costs incurred by undertaking refurbishment programmes necessary for the continued use of these ageing multiple units, particularly due to the necessity of handling and removing hazardous materials such as asbestos. In light of the high costs involved in retention, planners examined the prospects for the development and introduction of a new generation of DMUs to succeed the first generation.
In the concept stage, two separate approaches were devised, one involving a so-called railbus that prioritised the minimisation of both initial (procurement) and ongoing (maintenance and operational) costs, while the second was a more substantial DMU that could deliver better performance than the existing fleet, particularly on long-distance services. The initial specification developed for the latter type was relatively ambitious for the era, calling for a maximum speed of , a rate of acceleration compatible to contemporary EMUs, the ability to couple/work in multiple with existing EMUs, facilitate through-access for passengers, feature pressure ventilation, the ability to assist another failed unit, and to comprise either a three or four-car consist.
This specification led to the development of the experimental British Rail Class 210 diesel-electric multiple unit. However, to deliver the performance specified, it was found that relatively expensive equipment had to be used, particularly to provide sufficient speed, acceleration, and through-passenger access; it also had maintainability problems due to space limitations. Despite these shortcomings, it was recognised that a production fleet that was assembled from proven components would possess both a greater reliability level and lower maintenance costs; it was forecast to achieve an availability rate of 85 percent. As such, the type had sufficiently demonstrated a promising reduction in maintenance costs was achievable, especially once initial teething problems were dealt with, as well as the wider value represented by a new generation of DMUs in the reduction of ongoing costs for BR.
By 1983, experience with the Class 210 had influenced planners to favour the procurement of a new generation of DMUs, but also to adopt a new set of specifications somewhat less demanding than the prior set. Specifically, it was decided to lower the top speed from , as testing had shown that the higher rate brought no perceptible improvement in journey times due to the typically short distances between the stations that the type was intended to serve. Furthermore, it was determined that a propulsion system delivering per tonne would deliver sufficient acceleration. The requests for compatibility with other rolling stock were eliminated, although auto-coupling and auto-connecting functionality were added. In addition to a good ride quality, the specification included a sound level of 90dB when at full speed, an operational range of , and an interval between major overhauls of five years or .
In comparison to the previous generation of DMUs, which typically used a pair of engines for each power car, the new generation DMU would use only a single engine per car; sufficient cooling was also provided that even with one failed engine, a two-car unit could continue to perform typical services without incurring a major performance deficit. From an operational perspective, it was intended that the DMU could be assembled akin to building blocks, comprising between two and four cars that may or may not be outfitted with various passenger amenities such as toilets and luggage spaces.