The gravity model as a tool for decision making. Some highlights for Indian roads

Abstract

For many decades, there have been plenty of analyses all over the world about the relationship between socio-economic attributes and transport flows. One of the most fruitful tools is the gravity model, in the beginning used for road transport, but recently widely used for air transport and international trade. India is an outstanding example of complexity, with a mixture of megapolises and vast rural areas. Its road network shows plenty of six and four lane expressways spanning hundreds of kilometers, complemented by a dense web of State and local secondary and tertiary links. In the last decades, National and State Governments have improved vast tracts of roads, but there is still a huge gap. Investment priorities are usually decided on the ground of existing congestion or strategic issues, but not much on demand analyses. For ascertaining whether in India socio-economic structure and transport flows follow a common pattern, complete corridor OD matrices were calibrated from partial screen matrices for a sample of long-distance corridors (NH-1, NH-6, NH-8, NH-58, NH-73). These matrices were later analyzed by means of gravity models that included parameters such as population or GDP per district (as zone attributes) and road distance among district centroids (as friction factors). Several formulae were tested, and the best fit was selected. Results for main corridors are rather homogeneous, and rather consistent with research carried out in other countries. Simple formulae have a high explanatory capacity, even if the huge mega-cities of Delhi and Mumbai are included in the analysis. But results for rural corridors are much less consistent, probably due to a less mature structure in terms of spatial distribution and transport relationships.