The Resilience of Access

This work was first published in the Journal of Transportation Research Part D: Transport and Environment. View the paper here

While numerous studies have been completed to understand the reliability and resilience of transport networks, current assessments often neglect two things: the wider objective of the network (which is to allow people to travel between destinations of interest) and the variety of needs (and therefore destinations) of the people that the network serves. Yet, the transport network is all-but redundant if there are no operable destinations. Without considering the operational status of destinations, fixation on the network’s functionality can lead to a distorted understanding of the impacts that a disruption has on access and community function. Therefore, to better understand the resilience of a transportation network and its impacts on a community we must reconsider and broaden the approach to measure that resilience.

To address these gaps, our objective was to enhance the understanding of the role of the transportation network in community resilience. We achieve this by developing and demonstrating an approach to evaluate the direct and indirect impacts of a disruption on a transportation network and the community’s ability to access services. The approach is based on the ability to modify the transport network for an entire city to reflect potential damage (direct impacts), in a manner that is computationally efficient and therefore practicable to integrate into repeated hazard simulation. To measure the indirect impacts, we evaluate how a community’s access, and the equity of that access, changes as a result of the transportation network’s disruption and closures to essential services. This enables a better and broader understanding of how and where residents will be affected by potential hazards.

To demonstrate this approach with different types of hazards (earthquake liquefaction, pluvial flooding, and tsunami) we consider three cities: Seattle (WA, USA), Houston (TX, USA), and Christchurch (New Zealand). These case studies are used to demonstrate (1) how access and access equity changes across different demographic groups, incorporating uncertainty; (2) regions prone to isolation and their demographics composition; and (3), the potential for multi-criteria optimisation to aid decision-makers in the process of coordinating an equitable restoration program.
An interactive dashboard demonstrating our results is provided below.

The accessibility provided by the transportation network is an essential part of daily life. It enables people to access their education, employment, and daily needs as well as allowing emergency or other services to come to them. The implications of poor or inequitable access are evident even before a disaster strikes, with longer commute times being associated with reduced mental and physical health, and lower time resource to spend on other needs such as socialising or exercising. The role of the transportation network in providing access is most evident after a disruption when access is lost or significantly reduced.

In this paper, we presented an approach that looks beyond just the functionality of the transportation network and instead seeks to determine whether a community’s needs are being served in terms of access to services and amenities. We do this by evaluating the direct and, often overlooked, indirect impacts on communities after a disruption in the transportation network. Specifically, we consider how access and equity of access to key services changes over the time frame of a disaster. The underestimated importance of the transportation network is demonstrated through our case study results where we estimate that hundreds of thousands of residents could be isolated from critical amenities after a disruption in the network. Additionally, our three case studies demonstrate that initially equal access communities can become disparate after a hazard, often with disproportionate impacts on minority or vulnerable populations. By demonstrating the approach’s functionality within the three case studies, we determined that cities with robust and equitable initial access are likely to be more resilient to natural hazards. Therefore, in the context of increased and changing hazards, we must strive for intelligent urban design that prioritises the equity and quality of business-as-usual access, to not only improve our sustainability and public health, but also strengthen our community’s resilience.

Our approach leverages the recent advances in data availability and computational power which makes repeatedly simulating damage and disruption, at the link level, practicable. This ultimately enables transport & urban planners, and emergency managers to consider the wider implications of the transport network.
That is, we can consider how disruptions to roads and destinations will impact residents spatially throughout the city.

There are exciting opportunities for the future progress of this approach by incorporating interdependent infrastructure analysis. This approach will enable new avenues to aid with equitable and effective climate change adaptation within our cities. It can do this by improving the measurement of indirect impacts and the understanding of the effects that they will have on community resilience.
Improvements in access will begin to increase the health, well-being, safety, and livability of our cities. Therefore, we urge transport planners and emergency managers to broaden their view of the network and its resilience to also include and consider equitable access to key services.

Check out our dashboard here

M. J. Anderson, D. A. F. Kiddle, & T. M. Logan (2022). The Underestimated Role of the Transportation Network: Improving Disaster & Community Resilience. Transportation Research Part D: Transport and Environment.