Shifting perspectives: A comparison of travel-time-based and carbon-based accessibility landscapes

Abstract

Undoubtedly, climate change and its mitigation have emerged as main topics in public discourse. While accessibility planning is recognized for supporting sustainable urban and transport development in general, the specific challenge of reducing transport-related greenhouse gas emissions has rarely been directly addressed. Traditionally, accessibility is operationalized in line with the user perception of the transport system. Travel-time-based measures are considered to be closely linked with travel behavior theory, whereas CO2 emissions are not necessarily a major determinant of travel decisions. Given the changed prioritization of objectives, additional emphasis should be placed on the environmental costs of travel rather than solely the user costs. Accessibility analysis could account for this shift in perspectives by using CO2 emissions instead of travel time in the underlying cost function. While losing predictive power in terms of travel behavior compared to other implementations of accessibility, carbon-based accessibility analysis enables a normative understanding of travel behavior as it ought to be. An application in the Munich region visualizes the differences between travel-time-based and carbon-based accessibility by location, transport mode, and specification of the accessibility measure. The emerging accessibility landscapes illustrate the ability of carbon-based accessibility analysis to provide new insights into land use and transport systems from a different perspective. Based on this exercise, several use cases in the context of low-carbon mobility planning are discussed and pathways to further develop and test the method in cooperation with decision-makers are outlined.

Measuring just accessibility within planetary boundaries

“…U.S. In a similar vein, Kinigadner et al (2020Kinigadner et al ( , 2021 applied a carbon constrain to place-based accessibility (cumulative opportunities) using Germany's carbon reduction targets as thresholds and estimated the impacts on accessibility in multiple current and future scenarios. While losing their predictive power on individual's travel behaviour, emission-sensitive measures of accessibility provide understanding on the gap between the current and environmentally sustainable levels of accessibility, which is currently much needed in transport planning and policy.…”

“…Regarding this, it is important to consider overall sustainability effects systemically including whole lifecycle impacts and different time scales to obtain an accurate picture. For example, while private car usually prevails against public transport in travel-time based comparisons, incorporating a future emission budget into the optimization may shift this perspective to the opposite (Kinigadner et al, 2021). There is a lot of ground to cover in navigating and making visible such interlinkages and conflicting interests in accessibility research.…”