The single greatest problem of friction and wear in railroads occurs at the interface between the
wheels and the rails where the wheel flange contacts the rail, particularly in curves. It has been
estimated that the industry could save about $250 million annually from an effective program to
reduce flange/rail friction by lubrication or other means. About 1/3 of the savings would come
from increased fuel efficiency, 1/3 from reduced rail wear, and 1/3 from lower wheel wear. The
magnitude of savings could vary considerably from place to place depending upon grades,
curves, maximum speeds, and types of trains. Research with full-scale trains has shown that
effective spray lubrication of the rail can result in fuel savings of up to 25% on highly curved
track and about 5% on relatively straight track.
Flange lubrication also is expected to improve the safety of freight trains by lowering the chance
for derailment by reducing the forces that cause the wheel to climb the rail.
Although spray lubrication systems have been demonstrated successfully under controlled
conditions, practical problems have seriously limited their use. These problems include poor
durability of the spraying mechanism, difficulty in maintaining the system, and lack of
acceptance by train crews who fear loss of braking power or traction.
Another approach to rail lubrication uses wayside lubricators, which are permanently located
along curves in the tracks. Initial results with this system have been very promising, but
additional field trials are needed.
As concerns about the environment continue to increase, the development of affordable
biodegradable lubricants for rails grows in importance.
A second source of friction in freight cars occurs between the wheel tread and the top of the rail.
A system for top-of-rail lubrication has been developed recently, and it has been able to achieve
additional fuel savings of about 50% of those possible with flange lubrication. Current concerns
about top-of-rail lubrication include the high cost of the lubricant and possible adverse
interactions with the flange lubricant.
Another approach to reducing flange resistance is the use of radial or steerable trucks. This
approach usually is used only on new car fleets because of the large capital investment that
would be required for installed fleets.
While low friction is desired between the rail and the wheels on freight cars and between the
rails and the flanges on locomotives, high friction is needed between the tread of the locomotive
wheels and the rails. The recent introduction of locomotives with 4300- to 6000-hp engines and
AC asynchronous motors has produced a quantum increase in the power produced and available
at the railhead, but, at lower speeds (less than 20 mph), locomotives are limited to less than full
power because of low adhesion between the wheel and the rail. Translated into productivity, an
increase in adhesion from 35 to 40%, for example, could result in a 14% improvement in
potential trailing tonnage for a train ascending a 1% grade at 10 mph.
Possible approaches to improving adhesion include: