A rack railway (also rack-and-pinion railway, cog railway, or cogwheel railway) is a steep grade railway with a toothed rack rail, usually between the running rails. The trains are fitted with one or more cog wheels or pinions that mesh with this rack rail. This allows the trains to operate on steep gradients of 100% (45 degrees) or more, well above the 10% (5.7 degrees) maximum for friction-based rail. The rack-and-pinion mechanism also provides more controlled braking and reduces the effects of snow or ice on the rails. Most rack railways are mountain railways, although a few are transit railways or tramways built to overcome a steep gradient in an urban environment.
The first cog railway was the Middleton Railway between Middleton and Leeds in West Yorkshire, England, United Kingdom, where the first commercially successful steam locomotive, Salamanca, ran in 1812. This used a rack and pinion system designed and patented in 1811 by John Blenkinsop.
The first mountain cog railway was the Mount Washington Cog Railway in the U.S. state of New Hampshire, which carried its first fare-paying passengers in 1868. The track was completed to reach the summit of Mount Washington in 1869. The first mountain rack railway in continental Europe was the Vitznau-Rigi-Bahn on Mount Rigi in Switzerland, which opened in 1871. Both lines are still running.
Many different designs of rack rail and matching cog wheel have been developed over the years. Except for some early Morgan and Blenkinsop rack installations, rack systems place the rack rail halfway between the running rails, mounted on the same sleepers or ties as the running rails.
John Blenkinsop thought that the friction would be too low from metal wheels on metal rails even on level ground, so he built his steam locomotives for the Middleton Railway in 1812 with a 20-tooth, 3-foot (914 mm) diameter cog wheel (pinion) on the left side that engaged in rack teeth (two teeth per foot) on the outer side of the rail, the metal "fishbelly" edge rail with its side rack being cast all in one piece, in 3-foot (1 yd; 914 mm) lengths. Blenkinsop's system remained in use for 25 years on the Middleton Railway, but it became a curiosity because simple friction proved sufficient for railroads operating on level ground.
The Fell mountain railway system, developed in the 1860s, is not, strictly speaking, a rack railway, since it has no cogs with teeth. Rather, this system uses a smooth, raised center rail between the two running rails on steep sections of the line, which is gripped on both sides to increase friction. Trains are propelled by wheels or braked by shoes pressed horizontally onto the center rail, as well as by means of the normal running wheels.
The first successful rack railway in the United States was the Mount Washington Cog Railway, developed by Sylvester Marsh. Marsh was issued a U.S. patent for the general idea of a rack railway in September 1861, and in January 1867 for a practical rack where the rack teeth take the form of rollers arranged like the rungs of a ladder between two L-shaped wrought-iron rails. The first public trial of the Marsh rack on Mount Washington was made on August 29, 1866, when only one quarter of a mile (402 meters) of track had been completed. The Mount Washington railway opened to the public on August 14, 1868. The pinion wheels on the locomotives have deep teeth that ensure that at least two teeth are engaged with the rack at all times; this measure helps reduce the possibility of the pinions riding up and out of the rack.
The Riggenbach rack system was invented by Niklaus Riggenbach, who was working at about the same time as Marsh but independently. Riggenbach was granted a French patent in 1863 based on a working model, which he used to interest potential Swiss backers. During this time, the Swiss Consul to the United States visited Marsh's Mount Washington Cog Railway and reported back to the Swiss government with enthusiasm. Eager to boost tourism in Switzerland, the government commissioned Riggenbach to build a rack railway up Mount Rigi. Following the construction of a prototype locomotive and test track in a quarry near Bern, the Vitznau–Rigi railway opened on 22 May 1871. The Riggenbach system is similar in design to the Marsh system. It uses a ladder rack, formed of steel plates or channels connected by round or square rods at regular intervals. The Riggenbach system suffers from the drawback that its fixed ladder rack is more complex and expensive to build than those of other systems. Following the success of the Vitznau–Rigi railway, Riggenbach established the Maschinenfabrik der Internationalen Gesellschaft für Bergbahnen (IGB) – a company that produced rack locomotives to his design.
The Abt system was devised by Carl Roman Abt, a Swiss locomotive engineer. Abt worked for Riggenbach at his works in Olten and later at his IGB rack locomotive company. In 1885, he founded his own civil engineering company. During the early 1880s, Abt worked to devise an improved rack system that overcame the limitations of the Riggenbach system. In particular, the Riggenbach rack was expensive to manufacture and maintain, and the switches were complex. In 1882, Abt designed a new rack using solid bars with vertical teeth machined into them. Two or three of these bars are mounted centrally between the rails, with the teeth of the pinions rotationally offset from each other to match. The use of multiple bars with offset teeth ensures that the pinions on the locomotive driving wheels are constantly engaged with the rack. The Abt system is cheaper to build than the Riggenbach because it requires a lower weight of rack over a given length. However, the Riggenbach system exhibits greater wear resistance than the Abt. The first use of the Abt system was on the Harzbahn in Germany, which opened in 1885. It was also used on the Diakopto-Kalavryta railway in 1885, the Snowdon Mountain Railway in Wales in 1896 and in 1893 by the Japanese Government Railways on the section between Yokokawa and Karuizawa in the Usui Pass. It is used today on the Ikawa Line of the Ōigawa Railway. The pinion wheels can be mounted on the same axle as the rail wheels, or driven separately. The steam locomotives on the West Coast Wilderness Railway have separate cylinders driving the pinion wheel, as do the "X"-class locomotives on the Nilgiri Mountain Railway.
The Agudio rack system was invented by Tommaso Agudio. Its only long-lived application was on the Sassi–Superga tramway, which opened in 1884. It used a vertical rack with cog wheels on each side of the central rack. Its unique feature, however, was that the 'locomotive' was propelled by means of an endless cable driven from an engine house at the foot of the incline. It was converted to use the Strub rack system in 1934.
The Locher rack system, invented by Eduard Locher, has gear teeth cut in the sides rather than the top of the rail, engaged by two cog wheels on the locomotive. This system allows use on steeper grades than the other systems, whose teeth could jump out of the rack. It is used on the Pilatus Railway. Locher set out to design a rack system that could be used on gradients as steep as 1 in 2 (50%). The Abt system – the most common rack system in Switzerland at the time – was limited to a maximum gradient of 1 in 4 (25%). Locher showed that on steeper grades, the Abt system was prone to the driving pinion overriding the rack, causing potentially catastrophic derailments, as predicted by Dr. Abt. To overcome this problem and allow a rack to line up the steep sides of Mt. Pilatus, Locher developed a rack system where the rack is a flat bar with symmetrical, horizontal teeth. Horizontal pinions with flanges below the rack engage the centrally mounted bar, both driving the locomotive and keeping it centered on the track. This system provides a very stable attachment to the track, also protecting the car from toppling over even under the most severe crosswinds. Such gears can also lead the car, so even flanges on running wheels are optional. The biggest shortcoming of the system is that the standard railway switch is unusable, and a transfer table or other complex device must be used where track branching is needed. Following tests, the Locher system was deployed on the Pilatus Railway, which opened in 1889. No other public railway uses the Locher system, although some European coal mines use a similar system on steeply graded underground lines.