It was designed around a particularly ambitious set of requirements defined in a specification produced by British Rail (BR), construction of the first unit commenced during 1982.
By the beginning of the 1980s, British Rail (BR) operated a large fleet of first generation DMUs, which had been constructed in prior decades to various designs.
[7] While formulating its long-term strategy for this sector of its operations, British Rail 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.
[8] 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 & operational) costs, while the second was a more substantial DMU that could deliver superior performance than the existing fleet, particularly when it came to long-distance services.
[8] The initial specification developed for the latter type was relatively ambitious for the era, calling for a maximum speed of 90 mph (140 km/h), 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.
In order to deliver the performance levels that had been specified by BR, particularly in regards to maximum speed, rate of acceleration, and the desired through-passenger access, it was determined to be necessary to adopt relatively expensive equipment.
[8] The propulsion system was particularly affected; a total of four traction motors were necessary to achieve the acceleration and assistance goals; furthermore, extensive and heavy soundproofing was needed between the engine compartment and the passenger space, which proved an obstacle for maintenance tasks in this area.
[8] These issues, although individually relatively minor, cumulatively served to undermine the economic arguments being considered around the prospective procurement of the Class 210 by BR, and decreased the likelihood of a large production run.
[8] For production, it is highly likely that numerous refinements would have been introduced, such as its assembly from more proven components, and that such a fleet would possess both a greater reliability level and lower maintenance costs.
[8] Specifically, it was decided to drop the top speed from 90 to 75 mph (145 to 121 km/h), as testing had revealed the higher rate to deliver no perceivable improvement in journey times due to the typically short spacing of the stations the type was intended to serve.