According to Smart, although James Bond was able to drive a Mercedes-Benz 250SE on train tracks in Octopussy by simply having the tyres shredded by spikes, in the real world converting a road car into a train is much more involved process.
In fact, the company says that it took Interfleet around six months to model and engineer the ForRail conversion.
The car's alloy wheels and pneumatic tyres were replaced with a set of solid steel wheels measuring 22 inches in diameter and weighing 80 kilograms each.
As the ForRail would be entirely guided by railway tracks and junctions, Interfleet disconnected the car's steering wheel. To ensure that ForRail stayed on the tracks, the wheels were locked in place by aluminium supports that were welded between the axles.
Over the weekend, during a model train exhibition, the ForRail went into limited service along a 16 kilometre stretch of the Bluebell Railway, a privately run vintage train line that cuts through Sussex, UK.
Handily the gauge (or width of the tracks) on the Bluebell Railway is 1435mm, which isn't too far removed from the ForFour track of 1467mm at the front and 1429mm at the rear.
The ForRail was operated at all times by a licensed train driver and was run at low speeds to ensure everyone's safety. With the ForRail's job now down, the car will be converted back into a road-going car.
Daimler states, hopefully with a bit of tongue in cheek: "Smart and Mercedes-Benz do not encourage any individual to carry out similar modifications. It’s incredibly difficult."