The new companies which came into existence with the grouping in 1923 addressed once again the best way to serve lightly populated rural communities. The options available to them centred on various forms of light railcars. Two forms of propulsion were available, the internal combustion engine and the steam engine. Electricity, in many cases required too large an investment for the likely traffic on the intermediate routes in rural areas.
Steam railcars/railmotors surprisingly given early experiences, had a second opportunity to serve in the era of the big four!
http://rogerfarnworth.com/2024/06/26/steam-railmotors-part-6-after-the-grouping/