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.