Airport ground access and urban congestion: a paradox of bi-modal networks

Public transport systems with separated way, such as automated people movers or mass transit systems, play a fundamental role as far as airport ground access is concerned, due to high potential capacity and reliability of service time. It is widely recognized that those transport systems, introduced in cities already congested by car traffic, are able to attract only a little share of the urban transport demand due to the fact that they can take competitive advantage and tangible effects on urban mobility only under high congestion levels on the road network. These conditions are proper of congested urban networks, in particular when airports are located close to urban areas so as passengers can travel from/to airports using either the urban road network or the transit systems. This paper shows that, as far as regional and urban airports are concerned, when a new transit system with exclusive rights of way is introduced to enhance airport ground accessibility, a substantial modification of the road network is necessary both in terms of infrastructure and signal policies, to reduce the capacity of the streets in the parts of the town served by transit system in order to establish an efficient bimodal transport system.