British Rail Class 158
The British Rail Class 158 Express Sprinter is a diesel multiple unit (DMU) passenger train designed for regional express services as part of British Rail's Sprinter family of second-generation DMUs. Built by British Rail Engineering Limited (BREL) at its Derby Litchurch Lane Works between 1989 and 1992, the class comprises 182 units, including 172 two-car sets (subclass 158/0) and 10 three-car sets (subclass 158/9), each powered by two 350 hp diesel engines (Cummins NT-855-R5 or Perkins 2006-TWH) driving Voith T211r hydraulic transmissions, with some units later upgraded to 400 hp engines.[1][2] Introduced to replace older first-generation DMUs on non-electrified routes, the Class 158 entered service in 1990, initially with Network SouthEast and Regional Railways, offering improved acceleration, comfort, and capacity for routes such as those in Scotland, the Midlands, and Wales.[1] The units feature aluminium bodywork, air-conditioning in most cars, and a top speed of 90 mph (145 km/h), making them suitable for semi-fast and stopping services on secondary lines.[2] As of October 2025, approximately 171 Class 158 units remain in service across the UK, operated by train companies including East Midlands Railway, Northern, Transport for Wales, and ScotRail, with ongoing refurbishment programs addressing interior upgrades, accessibility improvements, and reliability enhancements to extend their operational life into the 2030s.[3][4][5] Notable recent developments include the fitment of variable-rate sanding equipment on South Western Railway's fleet to mitigate wheel slip in adverse weather, and discussions on potential replacements with battery or hydrogen alternatives as part of the UK's net-zero rail ambitions.[6][7]Background and Development
Design Origins
In the early 1980s, British Rail faced a pressing need to replace its aging first-generation diesel multiple units (DMUs), which dated from the 1950s and 1960s and suffered from high maintenance costs, outdated features like vacuum brakes and steam heating, and the presence of hazardous materials such as asbestos that made refurbishment prohibitively expensive.[8][9] To address this, British Rail pursued two parallel development approaches: a low-cost railbus concept using bus-derived components for branch line services, which evolved into the Pacer family (Classes 140-144), and a higher-specification DMU designed for regional express routes with improved comfort and performance.[10][9] The experimental Class 210 diesel-electric multiple units, trialed in 1982, significantly influenced the Sprinter family's design by highlighting the need for cost-effective alternatives to locomotive-hauled trains, though their high price led to revised specifications for production units.[10][1] These revisions included an initial top speed of 75 mph later upgraded to 90 mph for express variants like the Class 158, a single engine per car to simplify operations, and modular construction using proven bodyshell designs for easier maintenance and reduced lifecycle costs.[1][10] To select the optimal design, British Rail initiated competitive prototyping in 1983-1985, with British Rail Engineering Limited (BREL) at York developing the Class 150 units featuring Cummins or Perkins engines and Voith hydraulic transmissions, while Metro-Cammell at Washwood Heath built the rival Class 151 prototypes.[8] The BREL Class 150 emerged victorious due to superior reliability and alignment with operational needs, forming the foundational basis for the broader Sprinter production program, including the subsequent Class 158 Express Sprinter.[8][1]Specification and Production
Following the evaluation of prototypes derived from the Class 150 design, the final specifications for the British Rail Class 158 were refined to include both two-car and three-car configurations, optimized for regional express services. Each power car featured a Cummins NT-855-R5 inline-six turbocharged diesel engine rated at 350 horsepower, driving a Voith T211rz two-stage hydrokinetic hydraulic transmission to power the inner bogie. The units incorporated British Standard Institution (BSI) couplers to enable multiple working with other Sprinter-class DMUs.[1][11] In response to British Rail's tender process initiated in the mid-1980s to modernize secondary routes, an initial order envisioned up to 35 three-car units for Regional Railways, but due to budget constraints the order was adjusted, resulting in a total of 182 Class 158 units ordered from British Rail Engineering Limited (BREL), comprising 172 two-car sets and 10 three-car formations for higher-capacity routes such as those in Scotland operated by ScotRail.[1][12] Production took place at BREL's Derby Litchurch Lane Works, commencing in 1989 and continuing through to 1992.[2][13] The first production unit was completed in 1989, marking the start of assembly line output at Derby. Prior to revenue service, the Class 158 fleet underwent rigorous initial testing and certification, encompassing load trials, dynamic braking assessments, and speed trials up to the design maximum of 90 mph (145 km/h), alongside route approval processes to ensure compatibility with the British Rail network's infrastructure and signaling systems.[1][12] Entry into passenger service began in September 1990 with ScotRail, where the initial batch of units was allocated to routes including Edinburgh to Glasgow and extensions to Aberdeen and Inverness, replacing older locomotive-hauled formations.[1][12]Technical Description
Variants and Dimensions
The British Rail Class 158 diesel multiple unit was produced in two main variants: standard two-car sets and extended three-car sets. A total of 165 two-car units were constructed between 1989 and 1992 by British Rail Engineering Limited (BREL) at its Derby Litchurch Lane Works, designed primarily for regional express services with a focus on improved comfort and speed over earlier Sprinter classes. These units featured driving motor standard (DMS) cars at each end, each accommodating approximately 70 seats in a 2+2 configuration.[14][15] Seventeen three-car units were also built during the same period, incorporating an additional unpowered intermediate trailer standard open (TSO) car to boost passenger capacity to around 207 seats per set, making them suitable for busier routes. These three-car formations were initially intended for Network SouthEast operations but underwent modifications before widespread deployment. The structural design emphasized lightweight aluminum bodywork for better power-to-weight efficiency, with gangway connections allowing flexible coupling into longer trains if needed. The three-car units comprised the 158/9 subclass, with 10 allocated to Network SouthEast and 7 to Trans-Pennine services; two-car units were primarily the 158/0 subclass for Regional Railways, with some allocated to NSE without major adaptations.[15][1] Key physical dimensions of the Class 158 units are summarized in the following table, reflecting their compact footprint for secondary line operations while adhering to British loading gauge standards:| Dimension | Two-Car Unit | Three-Car Unit | Notes/Source |
|---|---|---|---|
| Length per car | 22.57 m | 22.57 m | Standard DMS/TSO car length; approximate 23 m in production specs.[1][11] |
| Overall length | 45.14 m | 67.71 m | Includes couplers; three-car variant provides ~50% more length for capacity.[1][16] |
| Width | 2.70 m | 2.70 m | Body width over doors and panels.[11][1] |
| Height (roof) | 3.78 m | 3.78 m | To top of roof; pantograph height not applicable as diesel unit.[1] |
| Weight (empty) | 75.6-77 tonnes (total) | 113.4-115.5 tonnes (total) | Two-car empty weight; per-car average 37.8-38.5 tonnes, varying slightly by engine fitment.[1][17] |