Congested urban transportation networks and emission paradoxes

In this paper, we identify three distinct paradoxical phenomena that can oc cur in congested urban transportation networks as regards the total emissio ns generated, which demonstrate that so-called 'improvements' to the transp ortation network may result in increases in total emissions generated. In p articular, we illustrate, through specific examples, the following: (1) the addition of a road may result in an increase in total emissions with no ch ange in travel demand, (2) the total emissions may increase with a decrease in travel demand and (3) the improvement of a road in terms of travel cost may result in an increase in total emissions without a change in the trave l demand. These examples demonstrate that the network topology, cost struct ure, as well as the travel demand structure must be taken into consideratio n in any policy system aimed towards the reduction of emissions due to moto r vehicles. (C) 2000 Elsevier Science Ltd. All rights reserved.