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Rack-And-Pinion Railways

Rack-And-Pinion Railways
A rack-and-pinion railway (also known as a cog railway) was one that employed a toothed track. The addition of the toothed rail – which was usually located centrally between the two running rails – enabled locomotives to traverse steep gradients over seven per cent, which remains to this day the maximum limit for standard adhesion-based railways.

Core to the operation of each rack-andpinion system was the engagement of the locomotive’s circular gears onto the linear rack. The rack and pinion therefore was essentially a means of converting the rotational energy generated by the train’s powerplant into linear motion on the rack. As both the rack-and-pinion gears had teeth, the system also acted as an additional form of adhesion to the track, with the inter-meshing teeth holding the vehicle in place when not in motion.

Rack-And-Pinion Railways

Due to the primary form of power traditionally being steam, for rack-andpinion systems to work the trains needed to be considerably adjusted. This modification stretched from the undercarriage of the train (so pinions could be installed) to the tilting of its boiler, cab and superstructure. Tilting was necessary as steam engine boilers require water to cover the boiler tubes and firebox at all times to maintain stability – something that is nigh-on impossible to achieve if the train isn’t level. As such, cog railway locomotives would lean in towards the track to counter the terrain’s gradient.
Today, while rare, rack-and-pinion systems are still in operation worldwide, albeit with a mix of steam engines and diesel/electric locomotives. One of the most famous is the Mount Washington Cog Railway, which we look at more closely in the boxout opposite.

A Mechanical Mountain Climber
The Mount Washington Cog Railway in New Hampshire, USA, was the first rack-and-pinion railway used to climb a mountain. Completed by Sylvester Marsh in 1869, the system is the second-steepest rack railway in the world, with a top gradient of 37.4 per cent. The railway runs 4.8 kilometres (three miles) up Mount Washington’s western slope, beginning at 820 metres (2,700 feet) above sea level and culminating just short of the peak at 1,917 metres (6,288 feet). The locomotive goes up at 4.5 kilometres (2.8 miles) per hour and descends at 7.4 kilometres (4.6 miles) per hour. Despite being built 144 years ago, this cog railway is still fully operational.