Transport for Wales considers converting Class 231 fleet into bi-mode units

Transport for Wales is examining plans to convert its Class 231 DEMUs into bi-mode units.

TfW Rail Ltd’s board was presented with a proposal for “hybrid conversion work” for the 11 units. The operator has a Hybrid Variation Agreement with manufacturer Stadler to serve an activation notice if it wishes to convert the units.

So far the notice has not been served. TfW has until April 30, 2026, to decide if it wishes to activate the notice.

A spokesman said: “If it does go ahead it will take up to four years to complete, with the all 11 units being converted from diesel only to bi-mode trains (pantograph conversion), one unit at a time.”

The existing lease from SMBC for the units, which have been in service since March 2023, expires in 2033. If they are re-leased until 2040, it would mean TfW could avoid having procure replacement units which would need to be bi-mode at least.

Converting the units would also reduce training requirements and changes to maintenance facilities, and avoid additional maintenance costs. It would also mean the units’ diesel engines not having to be used as much, cutting down on wear and fuel.

The Class 231s are being used on Coryton-Cardiff Queen Street and Rhymney line services on the South Wales Metro until overhead line equipment is energised, enabling Class 756 tri-mode units to take over.

They are then due to be moved onto Maesteg-Cardiff–Ebbw Vale and Cardiff-Cheltenham services.