This propane tank is 2.15m / 7' long

Propane tanks are used on railroads to supply fuel for 'switch heaters', that prevent track switches from icing up or filling up with snow.

Usually found near junctions, railroad crossings with other railroads, or 'crossovers', where trains can switch from one track to another.

They are also used occasionally to power generators to keep signals operating during an extended power failure.

You may also find them around industrial buildings that use propane and homes for heating.

These tanks add another detail that makes your railroad more visually interesting.