How did these unique transit systems help hefty locomotives scale steeper mountain slopes than ever before?
Arack-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 loc ated centrally bet ween the two running rails – enabled locomotives to traverse steep gradients over 7 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 t herefore was essentially a means of conver ting the rotational energ y generated by the train’s power plant into linear mot ion on the rack. As both the rack-and-pin ion gears had teeth, the system also ac ted as an additional form of adhesion to the track, with the inter-mesh ing teeth holding the veh icle in place when not in motion.
Due to the primary for m of power traditionally being steam, for rack-andpin ion systems to work the trains needed to be con siderably adjusted. This mod ification stretched f rom the undercarriage of the train (so pinions could be installed) to the tilting of its boiler, cab and superstructure.
Tilting was necessar y as steam engine boilers require water to cover the boiler tubes and fi rebox at all times to maintain stabilit y – something that is nigh-on impossible to achieve if the train isn’t level. As such, cog railway locomot ives wou ld lean in towards the track to cou nter the ter rain’s gradient.
Today, while ra re, rack-and-pin ion systems are still in operation worldwide, albeit with a mix of steam engines and d iesel/elec tr ic locomot ives. One of the most famous is the Mount Washington Cog Railway, which we look at more closely in the boxout opposite.
Rack and roll
Understand the anatomy of a rack-and-pinion locomotive now with our cutaway illustration
A mechanical mountain climber
The Mount Washington Cog Railway in New Hampshire, US, 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 up Mount Washington’s western slope, beginning at 820 metres above sea level and culminating just short of the peak at 1,9
