GB Railfreight’s Class 99 fleet enters final UK testing

GB Railfreight’s new Class 99 bi-mode locomotives have entered the final phase of testing in the United Kingdom, marking a pivotal moment in the operator’s multi-year programme to modernise its heavy freight fleet and cut carbon emissions on key routes.

From Spanish assembly lines to British test tracks

The Class 99 programme has progressed steadily from Stadler’s manufacturing base in Valencia to dedicated test facilities on the European mainland and now the UK network. Early prototypes completed initial dynamic trials at the Velim test circuit in the Czech Republic, with running focused on validating performance in both electric and diesel modes under controlled conditions.

More recently, the first completed locomotives have been shipped to British ports and moved on to test centres and depots for UK-specific approvals. Publicly available information shows that heavyweight test runs are now under way with Class 99 units operating on selected routes, often marshalled with existing locomotives to verify compatibility and control systems.

Industry coverage indicates that this milestone means the project has moved beyond factory acceptance checks into the final proving of the design in real-world conditions. The move into intensive UK testing is widely viewed as the last major hurdle before the locomotives join day-to-day freight operations.

Bi-mode design aims to cut emissions on core freight corridors

The Class 99 is based on Stadler’s Euro Dual platform and is designed to haul heavy freight trains using 25 kV AC overhead power where it is available, switching to an onboard diesel engine away from electrified sections. Technical data published by the manufacturer points to a significantly higher power output when running on electricity compared with diesel, allowing the locomotive to make maximum use of existing overhead wires.

GB Railfreight has stated in its public material that the new fleet forms a central part of its decarbonisation plans, replacing older diesel-only locomotives on key trunk routes. The operator has highlighted potential carbon savings where long portions of a journey can be worked electrically, supported by the use of renewable fuels such as hydrotreated vegetable oil in diesel mode.

The combination of electric operation on the main line and lower-carbon diesel away from the wires is expected to reduce overall emissions while maintaining the high tractive effort required for heavy aggregates, intermodal and infrastructure traffic. Analysts following the sector note that this approach reflects a wider trend in European freight, where bi-mode traction is seen as a practical way to reduce emissions without waiting for full network electrification.

Regulatory approvals and route proving near completion

Reports from specialist rail outlets indicate that the Class 99 has now cleared key regulatory steps for operation on Britain’s main line network. Authorisation has focused on safety systems, braking performance, electromagnetic compatibility and adherence to the country’s technical standards for new rolling stock.

With this framework in place, attention has shifted to route proving and operational testing. Trial workings are being used to demonstrate performance with realistic freight loads, confirm interaction with signalling and control systems, and verify that the locomotives can operate in multiple with existing fleets such as the widely used Class 66. Observers have noted test formations where Class 99 units run with conventional locomotives, allowing operators to gather data while retaining a proven fallback.

These late-stage tests are also being used to fine-tune software, driving techniques and energy management strategies. Industry commentators suggest that once reliability data from these runs meets the targets set by the leasing company and operator, the locomotives will be cleared for wider deployment across GB Railfreight diagrams.

Fleet renewal and operational implications for GB Railfreight

The arrival of the Class 99 fleet coincides with a broader reshaping of GB Railfreight’s locomotive portfolio. Company announcements have flagged the planned release of some older diesel classes to the secondary market as the new locomotives come on stream, indicating a structured consolidation around more modern traction.

In practical terms, the additional power and flexibility offered by the Class 99 is expected to allow heavier trains, more efficient use of electric corridors and potentially fewer locomotive changes en route. Commentators have pointed to flows such as intermodal services, construction materials and infrastructure trains as early candidates for the new traction, where high tonnages and partial electrification are common.

There are also implications for driver training and depot operations. Training programmes have been ramped up at key locations so that crews are ready ahead of entry into full service, while depots are being equipped to handle the maintenance regimes associated with the dual-mode technology. Publicly available planning documents and corporate material suggest that the fleet will be progressively introduced over several timetable periods rather than in a single step.

A milestone for low-carbon freight on Britain’s rails

Beyond GB Railfreight’s own operations, the final testing of the Class 99 is being watched closely across the sector as a test case for bi-mode heavy freight in Britain. While other dual- and tri-mode locomotives have already appeared on the network, the Class 99 is specifically optimised for high-haul freight duties and is expected to become one of the most powerful locomotives in regular use under the wires.

Industry analyses suggest that if the locomotives perform as intended, they could support broader policy goals to shift freight from road to rail by offering reliable, lower-carbon traction without waiting for full route electrification. The ability to operate long distances electrically, then continue to non-electrified terminals under diesel power, is seen as particularly attractive for ports, terminals and construction hubs.

As final tests continue, attention is turning to how quickly the fleet can move from trial operation into daily service. With authorisations in place and route proving advancing, the Class 99 programme appears to be entering its last pre-launch chapter, setting the stage for a new generation of low-carbon freight haulage on Britain’s railways.