Curve resistance (railroad)

[1] Curve resistance is typically measured in per mille, with the correct physical unit being Newton per kilo-Newton (N/kN).

In Germany, Austria, Switzerland, Czechoslovakia, Hungary, and Romania the term R - b is used in the denominator (instead of just R), where b is some constant.

For the US, AREMA American Railway Engineering ..., PDF, p.57 claims that curve resistance is 0.04% per degree of curvature (or 8 lbf/ton or 4 kgf/tonne).

Note that for empty rail cars (low wheel loads) the specific curve resistance is higher, similar to the phenomena of higher rolling resistance for empty cars on a straight track.

The Russian experiments plot curve resistance against velocity for various types of railroad cars and various axle loads.

However his results all show curve resistance decreasing with increasing speed in conformance with this expectation.

To experimentally find the curve resistance of a certain railroad freight car with a given load on its axles (partly due to the weight of the freight) the same car was tested both on a curved track and on a straight track.

A single test run can find the train resistance (force) at various velocities by letting the rolling stock being tested coast down from a higher speed to a low speed, while continuously measuring the deceleration and using Newton's second law of motion (force = acceleration*mass) to find the resistance force that is causing the railroad cars to slow.

So the specific force (the result) is the deceleration multiplied by a constant which is 1/g times a factor to account for the equivalent mass due to wheel rotation.

Астахов proposed the use of a formula which when plotted[15] is in substantial disagreement with the experimental results curves previously mentioned.

[note 2] The state of repair of the railhead and of the wheelset, and of the compatibility of the two as chosen for a given railway have a significant impact on the curve resistance.

Freight vehicles with very high axle loadings are often run slowly on relatively poor track with inaccuracies laterally and vertically and jointed rails that give rise to bounce and sway will have a very different performance profile.

The wetness of the rail from rain and from unintended lubricants such as leaf litter pulverised by the wheel/rail interface will reduce the rail drag - but will increase the risk that on powered axles, that driven wheels will lose adhesion.

There are also many railways, particularly tramways, where the radius of the curve is too small for the natural steering effect to succeed - resulting that the flange rubs against the side of the rail to force compliance to the curvature.