The Effects of Urban Road Capacity Expansions

The Effects of Urban Road Capacity Expansions


Anders Tonnesen, Institute of Transport Economics, Aud Tennoy, Institute of Transport Economics, Frants Gundersen, Institute of Transport Economics


We examine in detail the short-term and long-term mechanisms resulting from ongoing road-capacity expansions. Applying a case-study approach, we ask: What are the effects on road traffic volumes and GHG emissions of urban road-capacity expansions?


The effects of urban road-capacity expansions
Planning and construction of urban road capacity expansions are going on in most of the larger cities in Norway. The motivation for the projects is often to reduce congestion and/or local environmental problems, and in some cases to reduce GHG emissions by reducing congestions. However, as noted by Nolan and Lem (2002), increases in capacity on urban highways are likely to reduce the time cost of travel, thereby resulting in increased traffic volumes. In this project we examine in detail the short-term and long-term mechanisms resulting from an ongoing road-capacity expansion. Applying a case-study approach, we ask: What are the effects on road traffic volumes and GHG emissions of urban road-capacity expansions? Several sources of data have been applied, among these, register data on housing, population density and commuting patterns, as well as registration of traffic volumes and traffic flow on defined road stretches. The project also applies qualitative interviews and document studies of county plans, municipal plans and zoning plans.

Our main hypothesis relate to the mechanisms road-capacity expansions are believed to cause in pressured urban transport systems:
 modal shifts towards higher car driver shares and longer travels causing increased road traffic
 longer commutes causing increased road traffic
 more developments of housing, workplaces, retail etc. further from the city centre as travel time by car are reduced, causing increased traffic volumes
 more car-based location of new developments, causing increased traffic volumes

The project takes departure in the existence of a competitive relationship between the modes of transport. This implies that if conditions for car use are or become better, compared to conditions for using other modes, the shares of the car travel mode will be higher (Downs, 1962; Mogridge, 1997; Nolan and Lem, 2002). If travelling by other modes becomes relatively better than by car, the shares of those travel modes will increase. This, in turn, also has consequences for land-use patterns, as high car-shares to a larger extent facilitates housing, retail and workplaces in distant locations.

The Norwegian case – road-capacity expansion in Ålesund
The city of Ålesund is located at the west coast of Norway. With 46 000 inhabitants within its borders, the city municipality is 13th largest in Norway. In the research project, a road-capacity expansion west of Ålesund city, in an area called Blindheim-Breivika, is explored. Main components in the road project, which was completed in 2002, are two tunnels and a two-level interchange.

Severe rush hour overload and congestion were main arguments for the road-capacity expansion. Anticipating steep population growth, followed by steadily worsening conditions for car-driving, the need for a road-capacity expansion was emphasised in the 1990’ies (Municipality of Ålesund 1993). It was then concluded that with the planned new road system there would be substantial capacity reserves for handling future traffic growth.

Turning to the present, traffic in the Blindheim-Breivika area is again described as congested (National Road Authorities 2013). Traffic counts show how there has been a steady increase in number of cars passing through the tunnels since they were taken into use. In depth analysis also reveal how the areas that according to theory would benefit most from the road expansion have been highlighted in policy documents as sites for new development. After the completion of the road-capacity expansion these areas have also been at the higher end in terms of new house building in the region. Through the in-depth analysis, we illustrate how the quality of the transport system affects both travel behaviour and land-use patterns.

Downs, A. (1962) The law of peak-hour expressway congestion. Traffic Quarterly, Vol. 16, pp. 393-409.
Noland, R. B. & L. Lem, L. L. (2002) A Review of the Evidence for Induced Travel and Changes in Transportation and Environmental Policy in the US and the UK. Transportation Research D, Vol. 7, No. 1, Jan. 2002, pp. 1-26.
Mogridge, M. J. H. (1997) The self-defeating nature of urban road capacity policy. A review of theories, disputes and available evidence. Transport Policy, 4 (1), 5-23
Municipality of Ålesund (1993) Municipal plan for the Spjelkavik area. Approved by the city council 07.10.93. Municipality of Ålesund
National Road Authorities (2013) Concept study of the transport system in Ålesund. National Road Authorities


Association for European Transport