Novel approaches to forecasting the demand for new local rail services

Revealed Preference (RP) studies based on actual behaviour suffer from a number of statistical problems. Furthermore, RP methods are of little use when the effects of a new or radically altered service need to be considered. As a result, for a case study of demand forecasting for new passenger rail services, a new approach has been developed. The present starting point is to seek what the authors call Stated Intentions (SI) responses as to the likely usage of a new rail service. However, due to a combination of systematic biases, these responses may be taken to be gross overestimates. A check on the biases of this SI data may be supplied by a Stated Preference (SP) survey. Respondents are asked to make hypothetical choices which are sufficiently complex for there to be little chance of policy bias. It is ensured that choices presented contain useful ‘boundary values,’ being the relative valuation for which respondents would be indifferent between two offered alternatives. It is, however, crucial to ensure that the SP survey is simple enough for respondents to manage, since excessive error variability in the responses will cause the calibrated coefficients to be rescaled, presenting problems for forecasting. From the SP surveys, it is estimated that SI data overstates usage of new rail services by around 50%, even if it is assumed that nonrespondents to the SI survey are nonusers. It is concluded that an SI/SP approach can potentially provide accurate forecasts, but there are a number of practical constraints that may prevent this.