A spline function classes suitable for transport demand models

Abstract

The paper present a spline function class specifically suitable for the estimation of time and cost attributes in transport demand models with a long distance domain. The function class is designed to be monotonic decreasing in utility and have monotonic and marginal decreasing elasticities. The properties are obtained by calculating separate scaling factors and interception points at each spline knot. The resulting function class can handle a wide range of cost-damping structures, which cannot be absorbed using traditional linear-in-parameter forms or non-linear forms such as the Box-Cox function class. The function is particularly useful for models with a semi-long to long distance destination domain for which heavy damping in the tail is likely to be found. The function class is implemented in the new Danish National Model and we present simulation as well as estimation results from the National Model.