Railroad Spiral Design and Performance

This paper reviews forms of spiral geometry that have been used and proposed as transition shapes in railroad tracks and compares them with respect to dynamic performance and spiral length. The dynamic performances that are compared were calculated using the Gensys rail vehicle motion simulation program and a well known model of the Eurofima coach. The results illustrate: 1) the dynamic disturbance caused by the discontinuity of first derivatives of track curvature and twist with the conventional ‘linear’ spiral; 2) the better dynamic performance of other simple forms of spiral including the virtually perfect performance of two of those forms; and 3) the amounts by which lengths of alternative spirals exceed that of the conventional ‘linear’ spiral for the example transition..