GB Railfreight Class 99 Bi-Mode Locomotives Enter Final UK Testing for Low-Carbon Freight

GB Railfreight has moved its new Class 99 bi-mode locomotives into final UK testing, a key step toward cutting carbon emissions on Britain's heavy freight corridors. Built by Stadler, these locomotives can run on 25 kV AC overhead electric power where available and switch to a diesel engine for non-electrified sections. The fleet is designed to replace older diesel-only units on trunk routes, using electric traction for the main line and lower-carbon fuels like hydrotreated vegetable oil for the rest. The Class 99 is based on Stadler's Euro Dual platform and is optimized for high-haul freight duties. Early prototypes completed dynamic trials in the Czech Republic, and the locomotives have now cleared UK regulatory approvals for safety, braking, and electromagnetic compatibility. Route proving with realistic loads is underway, often paired with existing Class 66 locomotives for fallback. The fleet is expected to enable heavier trains, fewer locomotive changes, and measurable carbon savings on routes with partial electrification. Industry observers see the Class 99 as a test case for bi-mode heavy freight in Britain. If successful, it could support policy goals to shift freight from road to rail without waiting for full network electrification. GB Railfreight plans a phased introduction over several timetable periods, with driver training and depot upgrades already in progress. The project represents a practical, near-term path to lower emissions in one of the harder-to-abate transport sectors.