Between 19 the company took delivery of 4 British built diesel locomotives to complement the steam fleet at a cost of £250,000 each. The original carriages were open above the waist and had canvas curtains, which provided little protection against the elements.These locomotives are powered by 320 Horsepower (238 k W) six cylinder turbocharged Rolls Royce diesel engines of 12 litres capacity. Between 19 the superstructure of the original carriages was modified to produce the enclosed bodies.The solution is to mount a toothed rack between the running rails and provide a cog (pinion) on the locomotive.

Rather than a revolutionary design, the bogies represent an incremental improvement to an existing design that has been in passenger service since 1986 and latterly improved in 2006 on the old carriage number 10 and the summit project flatbed truck.

In this way Hunslet have built on a solid safety record but improved the performance of this safety critical piece of equipment.

Some of the original carriages have updated with new bodies constructed on them for new Heritage Steam Experience.

A Traffic Controller at Llanberis, who is responsible for the overall movement of traffic, controls the movement of trains.

The total track length is 7.53 kilometers with a steepest gradient of 1 in 5.5 (or 1 meter rise every 5.5m travelled).

Snowdon Mountain Railway is the only public rack and pinion railway in the United Kingdom.

These new coaches have been designed and built in the UK by a partnership between Garmendale Engineering Limited of Ilkeston, Derbyshire and the Hunslet Engine Company, to a performance specification defined and project managed by the Railway.

Not only do the carriages boast higher levels of passenger safety, space and comfort, but the manufacturing process is a world first in the rail industry.

Each of these carriages had a capacity of 56 passengers, plus a guard.