While the alignment of new railways should be designed to meet future demands, an unnecessarily high standard may make a project too expensive and may cause an undesirable impact on the environment. Hence, the alignment should be optimised with great care when building new lines. In this study, equally costly alignment alternatives are compared. The cost is assumed to be correlated to the extent to which existing obstacles along a new alignment must be removed. With this approach, longer transition curves require smaller curve radii. A power car, a tilting coach and a non-tilting coach have been studied. Vehicle reactions have been simulated with dynamic vehicle/track computer models. passenger comfort (P_CT) has been used as object function. Vertical forces, guiding forces, track shift forces and wheel climbing rations have been used in boundary conditions. It was found that the following conditions favour longer transition curves: low roll coefficients of the vehicles and body tilt systems, large angles between adjacent straight lines, and obstacles in the middle of the curves (rather than near the ends) even though the radii must be reduced.
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