On railways, the axle load is the maximum weight of a train per pair of wheels allowable for a given section of track. The maximum axle load is related to the strength of the track, which is determined by weight of rails, density of sleepers and fixtures, train speeds, amount of ballast, and strength of bridges. Because track and especially the rails are expensive, it is desirable to optimise the track for a given axle load. If the track is overloaded by trains that are too heavy, it can be destroyed in a short time. It is convenient for the steelworks that rails are made in a limited number of sizes, so that a perfect match of rail weight and axle load is rarely achieved. New rail is often reserved for heavy main line use, which releases good but lighter rail that can be cascaded for lighter duties on branch lines. The lightest rail cascaded from the lightest branch lines may have no railway use other that for structural items such as fenceposts, telegraph posts and for reinforcing concrete.
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United Kingdom
Track
Light railways were built with rail weighing as little as 30 lb/yard but main lines used much heavier rail. On former British Rail lines the rail is mostly 90 lb/yard or 120 lb/yard.
Locomotives
In British Rail days most diesel locomotives were built to a maximum axle load of 19 tons (19.3 tonnes) so the maximum locomotive weight was 76 tons (77.2 tonnes) for a four-axle locomotive and 114 tons (115.8 tonnes) for a six-axle one. Higher axle loads are now permitted, e.g. the Class 67 locomotive is a four-axle machine weighing 90 tonnes, giving 22.5 tonnes on each axle.
Australia
Example 1
The new branch line from Blackwater, Queensland to Rolleston is being built in 2005 to haul the following:
- rail: 50 kg/m — (choice limited to 50 kg/m or 60 kg/m)
- sleepers: concrete
- sleepers per kilometre : unknown
- max speed: 80 km/h
- wagon axle load: 26 t
- locomotive axle load: 20 t
- swingnose crossings at turnouts: unknown
- traffic: 8 Mt/yr
- length of line: 110 km
- cost of line: US$185.5 million
- see IRJ May 2005
Roads
The term axle load is also applicable to trucks which is complicated by the fact that trucks may have more than two wheels per axle.
See also
External links
- Managing rail degradation on the Malmbanan, Thomas Nordmark and Dr Per-Olof Larsson-Kraik, Railway Gazette International June 2007.
