A cog railway is a railway which is equipped with a toothed center track which articulates with a cog underneath the locomotive. The cog and track create more traction for the train. Such railways can be found in many regions of the world, and while they are often operated as novelties because trains are less heavily used for transport, some do continue to be used in practical applications.
The main reason to install a cog railway is a concern that a train may have difficulty making its way up a grade. In this case, using the cog and center track will keep the train from slipping as it goes up or down the grade. Cog railways can be used on mountainsides to allow a train to go up and down the mountain reasonably safely, and they are also used in urban and rural settings where a grade is steep enough that a conventional train might not be able to navigate it.
Speed is a limitation with a cog railway. The train can generally only move fairly slowly, because the articulation of the cog and track prevents rapid progress. The locomotive may push or pull the cars, depending on whether it is going up or down hill and the preferences of the operator. Thanks to the cog and track, the locomotive has excellent braking ability, which can increase safety significantly.
Also known as a rack and pinion or rack railway, a cog railway can be used to move people and goods in an area where other vehicles might not be able to function. On a mountain, for example, cars and trucks might not be able to navigate. Alternatives to cog railways include gondolas and lifts, along with cable railways.
Cog railways operated as novelties for the tourist trade can be found in many communities. Often, a steam engine is used for additional novelty, although diesel locomotives can be applied as well. If a steam engine is used, visitors may be able to see a curious variation on locomotive design developed specifically for the cog railway. To function properly, the boiler of a steam engine must be relatively level, and in the case of a cog railway, a normally positioned boiler will tilt as the train moves uphill. To compensate for this, some locomotives on cog railways have tilted boilers which look misaligned on level ground, but which move into a level position as the train climbs up a hill, ensuring that the boiler will work right when the train needs power most.