Cost Benefit Analysis (CBA) plays a role in the evaluation of road investment proposals in most countries. There does now seem to be a general tendency to try to extend the types of investment to which CBA (or kindred approaches) is applied, from pure investment in building of new roads, over decisions about design standard, to choice of maintenance standard. This paper addresses the assessment of time gains in the latter types of cases. The author shows how resulting time gains are a result of a close interrelation between speed choice, driving comfort and values-of-time, and discusses how such investments can be evaluated to avoid double-counting and systematic underestimation of benefits. In CBA, time gains are known to produce a major part of the user benefits that are balanced against investment (and other) costs. As a consequence, research into theory, and empirical estimation, of values-of-time has been conducted in many countries. The resulting values are known to comprise two inseparable components: the "resource" value of time as such, and a "quality adjustment", reflecting the circumstances under which the time is spent. For practical CBA, the estimated (average) values-of-time are typically multiplied by average estimated time gains from the investment, to obtain an estimate of the consumer surplus generated. This method is relevant when the investment in question reduces travel time at basically constant driving comfort, as e.g., by introducing a shortcut in a network of homogeneous standard. Many measures, however, induce time gains for road users by "allowing" a higher travel speed, or rather, reducing the "comfort-price" of using a higher speed. (Comfort is used here in a broad sense, covering also aspects such as subjective safety, perceived risk of enforcement etc..). In those cases, the standard method for assessment is less applicable, since the time gain actually is achieved by a comfort improvement, which in turn implies a change in value-of-time. Nevertheless, time gains constitute a major part of the user benefits induced. Thus, also those time gains have to be (properly) assessed, and included in the CBA. This paper shows how travel time (gains) and value-of-time is related through driving comfort and speed choice, and discusses how this may be considered in assessment.
Abstract