Diesel engines on passenger trains could be replaced by battery power-packs to eliminate carbon emissions over the next few years - engineers are already preparing an experimental unit to be trialled on Greater Anglia.

The new Bimode diesel/electric units on Greater Anglia regional services are essentially electric trains with a diesel generator unit in the middle that provides the electricity to drive the motors where they cannot pick up power from overhead wires.

It would be fairly easy to replace the diesel generator unit with a battery unit - and that could be trialled in the near future.

Greater Anglia's Stadler-built Bimode and Intercity trains are owned by leasing company Rock Rail which is working with Stadler to develop the battery unit.

Seven years ago an experimental battery train was trialled on passenger services between Manningtree and Harwich - but at that time battery technology meant that the range of these trains was limited. They could run on services of up to about 50 miles return - but no longer.

Battery range for trains is still some way short of what it is for cars - at the moment it is about 70 miles and recharging is done while the train is under overhead wires.

In theory that makes it an option for some shorter routes like the Sudbury or Felixstowe branches, but to recharge it would ideally need to travel a distance under electric power.

Stadler is still working with Rock Rail on battery power, but these trains are likely to emerge over the next few decades.

The government has said diesel-only trains will have to be phased out by 2040 and all diesel power on the railways, including Bimode trains, is likely to be gone by 2050. The new Stadler trains are expected to stay in service until the 2060s, so batteries or hydrogen power banks will be needed eventually.

One option that has already been used on some trains is having Trimode traction - trains that run on electric power, battery, or diesel power. That could turn out to be short to medium term option on longer non-electrified routes to reduce diesel fumes as much as possible.