How a bespoke diesel-electric locomotive replaced outdated fleets to haul nuclear waste across Britain.
In short: When Direct Rail Services needed a modern, efficient replacement for its aging Class 20 locomotives, it turned to Stadler Rail to build a custom solution. The resulting Class 68, or UKLight, was engineered to navigate strict British loading gauges while delivering the power required for heavy freight and passenger operations.
By 2009, Direct Rail Services (DRS) recognized that its existing fleet, including the Class 20 and the inefficient Class 66, could no longer meet its operational needs or evolving EU emission standards. Seeking a versatile replacement capable of hauling nuclear flask trains through 2036, DRS collaborated with Stadler Rail Valencia to adapt the existing Eurolight platform. The resulting Class 68 was designed specifically for the British network, requiring significant modifications to fit within restricted loading gauges and achieve a top speed of 100 mph.
A key engineering challenge was the transition from a Co-Co wheel arrangement to a four-axle configuration. Through a low center of gravity and balanced weight distribution, the locomotive minimizes weight transfer between axles, ensuring consistent tractive effort. The propulsion system features a 3,800 hp Caterpillar C175-16 engine paired with an ABB-built traction package. To reach the 100 mph target, engineers relocated axle-hung traction motors to the body, successfully reducing unsprung mass. The unit also includes an electric train supply of up to 500 kW, allowing it to haul large passenger trains like the Class 390.
Since its introduction in 2014, the Class 68 has proven highly effective across diverse roles, from specialized nuclear waste transport to passenger services for operators like Chiltern Railways and TransPennine Express. The fleet has undergone various upgrades, including the integration of AAR push-pull equipment for carriage compatibility. Looking forward, the introduction of automatic start-stop technology in 2026 aims to further mitigate noise and pollution, demonstrating the platform's ongoing evolution as a cornerstone of British rail logistics.
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Sources
- Summary by Intellect · source: British Rail Class 68
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