The British Rail Class 158 Express Sprinter is a diesel multiple unit (DMU) passenger train. It is a member of the Sprinter series of regional trains, produced as a replacement for British Rail's first generation of DMUs; of the other members, the Class 159 is almost identical to the Class 158, having been converted from Class 158 to Class 159 in two batches to operate express services from London Waterloo to the West of England. The Class 158 was constructed between 1989 and 1992 by British Rail Engineering Limited (BREL) at its Derby Litchurch Lane Works. The majority were built as two-car sets, some three-car sets were also produced. During September 1990, the first Express Sprinters were operated by ScotRail; the type was promptly introduced to secondary routes across the Midlands, Northern England, Wales and the South West. The Class 158 enabled the replacement of large numbers of elderly DMUs but also several locomotive-hauled trains as well; this was partially accomplished via the cascading of existing Sprinter units onto other routes. To capitalise on the Class 158's improved onboard amenities in comparison to other rolling stock in use for regional services, the Alphaline branding was launched during the mid-1990s; it was also used for a time in the post-privatisation era. As a result of British Rail's privatisation in the mid 1990s, the Class 158s were divided amongst various newly-created operators broadly along their existing routes. Due to their relatively young age at that time, most operators elected to retain them for the following decades. Several, such as Northern Rail and Arriva Trains Wales, had their Class 158 fleets modernised and refitted with various new facilities, such modifications often including greater accessibility, onboard passenger information systems, WiFi connectivity, and toilet retention tanks. By the 2020s, many Class 158 operators have stated their intent to replace the type with newer rolling stock, such as the Class 170 Turbostar, Class 185 Desiro, and Class 197 multiple units. Background 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. 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