What to assess to model the transport impacts of urban growth? A Delphi approach to examine the space-time suitability of transport indicators

Selection of right transport impact indicators of urban growth is challenging because the impacts vary both geographically and temporally. For example, congestion might be a problem in inner-city areas in a short-term but might not be detectable in a regional context event in the long-run. This paper contributes to address this challenge. First, the study systematically selects 23 transport impact indicators through a review of 62 indicators identified from the literature. Second, it evaluates and classifies their suitability in terms of space–time dyads through a two-round of Delphi survey involving 29 international experts. The experts reached a consensus that 12 (52%) indicators are suitable in various space–time dyadic combinations. Only “travel time” was identified as a suitable indicator for all three spatial (local, city, region) and two temporal (short-, long-term) scales. The findings serve as a guide for decision makers, transport modelers and planners to adopt indicators according to their scale of operation, and thus simplify the daunting task of suitable indicator selection process.