Supply Curves for Urban Road Networks – a rejoinder.

Professor Hills is not quite correct to suggest that the origins of our research lay in his criticism (Hills, 1993) of Evans’ use of monotonic speed- ¯ ow relationships (Evans, 1992). Our interest lay in the more general use of area speed-¯ ow relationships in strategic models, of which Evans’ work was an example. However, our research bene® ted from Hills’ analysis, and from his subsequent contributions to our attempts to clarify de® nitions in this problematic area. It is unfortunate, therefore, that there are still differences in our understandng of these de® nitions. The diOEerences between us relate to six key issues, which we consider in turn below.