Revisiting modal split as an urban sustainability indicator using citizen science

Abstract

This paper discusses three uses of modal split indicators, and illustrates how it evolved from a technical, intermediate step in transport analysis, over a measure of transport system efficiency to a symbolic urban sustainable mobility indicator. A framework which includes 11 factors is presented and applied to the different uses of the modal split indicator. Besides the comparison of the three main uses of modal split in research and practice, this contribution focuses on a citizen science project (Straatvinken) in the region of Flanders, Belgium. In this project thousands of citizens carry out traffic counts. While the project was initially set up to monitor modal split targets in the urban area of Antwerp, the emphasis shifted towards street liveability. This is visible in the fact that the citizen science project added a narrative-based liveability survey to capture experiences with and evaluations of the liveability at street level. The case illustrates that citizen science is, besides a tool to address data gaps, also an approach to increase the validity of indicators. The reason is that citizen science, which seems to be underexplored in transport studies, differs in what gets measured, how it is measured and why. This approach has proven to provide a fine-grained, integrated assessment of street-level changes in the composition and intensity of the traffic and their effects on the perceived liveability. We argue that it strengthens and complements traditional modal split measurements at the regional or urban level, which typically rely on the modelling of individual mobility behaviour based on household travel surveys. Traditional approaches allow observing broad trends in mobility choices at the regional level, but they do not provide insights in how those individual choices translate into effects at street level. Although often initiated out of certain sustainability concerns, existing modal split models do not reveal how an observed modal shift at the regional level affects the perceived liveability or sustainability at street level.