Characterization and Assessment of Transportation Diversity: Impacts on Mobility and Resilience Planning in Urban Communities
Rahimi Golkhandan, Armin
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A transportation system is a critical infrastructure that is key for mobility in any community. Natural hazards can cause failure in transportation infrastructure and impede its routine performance. Ecological systems are resilient systems that are very similar to transportation systems. Diversity is a fundamental factor in ecological resilience, and it is recognized as an important property of transportation resilience. However, quantifying transportation diversity remains challenging, which makes it difficult to understand the influence of diversity on transportation performance and resilience. Consequently, three studies are undertaken to remedy this circumstance. The first study develops a novel approach – inspired by biodiversity in ecological stability theory – to characterize and measure transportation diversity by its richness (availability) and evenness (distribution). This transportation diversity approach is then applied to New York City (NYC) at the zip code level using the GIS data of transportation modes. The results demonstrate the variation of transportation diversity across the city. The characterized inherent and augmented complementarities start to uncover the dynamics of modal compensation and to demonstrate how transportation diversity contributes to this phenomenon. Moreover, the NYC zip codes with low transportation diversity are mainly in hurricane evacuation zones that are more vulnerable. Consequently, low transportation diversity in these areas could affect their post-disaster mobility. In the second study, the influence of transportation diversity on post-disaster mobility is examined by investigating the patterns of mobility in New York City one month before and after Hurricane Sandy using Twitter data. To characterize pre- and post-Sandy mobility patterns, the locations that individuals visited frequently were identified and travel distance, the radius of gyration, and mobility entropy were measured. Individuals were grouped according to the transportation diversity of their frequently visited locations. The findings reveal that individuals that lived in or visited zip codes with higher transportation diversity mostly experienced less disturbance in their mobility patterns after Sandy and the recovery of their mobility patterns was faster. The results confirm that transportation diversity affects the resilience of individual post-disaster mobility. The approach used in this study is one of the first to examine the root causes of changes in mobility patterns after extreme events by linking transportation infrastructure diversity to post-disaster mobility. Finally, the third study employs the transportation diversity approach to investigate modal accessibility and social exclusion. Transportation infrastructure is a sociotechnical system and transport equity is crucial for access to opportunities and services such as jobs and infrastructure. The social exclusion caused by transport inequity could be intensified after natural disasters that can cause failure in a transportation system. One approach to determine transport equity is access to transportation modes. Common catchment area approaches to assess the equity of access to transportation modes cannot differentiate between the equity of access to modes in sub-regions of an area. The transportation diversity approach overcomes this shortcoming, and it is applied to all transportation modes in NYC zip codes to measure the equity of access. Zip codes were grouped in quartiles based on their transportation diversity. Using the American Community Survey data, a set of important socioeconomic and transport usage factors were compared in the quartile groups. The results indicated the relationship between transportation diversity and income, vehicle ownership, commute time, and commute mode. This relationship highlighted that social exclusion is linked with transport inequity. The results also revealed that the inequity of the transport system in zip codes with low transportation diversity affects poor individuals more than non-poor and the zip codes with a majority of black and Hispanic populations are impacted more. Further consideration of the impacts of Hurricanes Irene and Sandy in NYC shows that people in areas with a lower transportation diversity were affected more and the transport inequity in these areas made it difficult to cope with these disasters and caused post-disaster social exclusion. Therefore, enhancing transportation diversity should support transport equity and reduce social exclusion under normal situations and during extreme events. Together, these three studies illustrate the influence of transportation diversity on the resilience of this infrastructure. They highlight the importance of the provision and distribution of all transportation modes, their influence on mobility during normal situations and extreme events and their contribution toward mitigating social exclusion. Finally, these studies suggest that transportation diversity can contribute to more targeted and equitable transportation and community resilience planning, which should help decision-makers allocate scarce resources more effectively.
General Audience Abstract
Transportation systems are very important in every city. Natural disasters like hurricanes and floods can destroy roads and inundate metro tunnels that can cause problems for mobility. Ecological systems like forests are very resilient because they have experienced disturbances like natural disasters for millions of years. Ecological systems and transportation systems are very similar; for example, both have different components (different species in an ecological system and different modes in a transportation system). Because of such similarities, we can learn from ecological resilience to improve transportation resilience. Having a variety of species in an ecological system makes it diverse. Diversity is the most important factor in ecological resilience, and it is also recognized as an important factor in transportation resilience. Current methods cannot effectively quantify transportation diversity – the variety of modes in a system – so determining its impact on transportation resilience remains a challenge. In this dissertation, principles of ecological diversity are adapted to characterize transportation infrastructure to develop a new approach to measure transportation diversity; metrics include the availability of transportation modes and their distribution in a community. The developed approach was applied in New York City (NYC) at the zip code level. Locations with low transportation diversity (fewer modes and/or unequal distribution) were identified, and most of these zip codes are located in hurricane evacuation zones. Consequently, these zip codes with the least diverse transportation systems are the most vulnerable, which can cause serious issues during emergency evacuations and the ability of people to access work or essential services. Therefore, in a city hit by a natural disaster, understanding the relationship between people's mobility and a transportation system's diversity is important. Twitter data was used to find the places that people in NYC visited regularly for one month before and one month after Hurricane Sandy. Subsequently, using different methods, the pre- and post-disaster mobility patterns of these individuals were characterized. The results show that after the disaster, individuals had a higher chance of maintaining their pre-disaster mobility patterns if they were living in and/or visiting areas with high transportation diversity. Based on these findings, we confirmed the influence of transportation diversity on post-disaster mobility. In addition, the transportation infrastructure should provide equitable service to all individuals, during normal operations and extreme events. One of the ways to determine this equality is equity of access to transportation modes. Hence, transportation diversity was used as an indicator for equity of access to transportation modes to overcome the limitations of current methods like catchment area approaches. NYC zip codes were grouped based on their transportation diversity and a set of important socioeconomic and transport related factors were compared among these groups. The comparison of socioeconomic and transport related factors in zip codes showed that the zip codes with lower transportation diversity are also more socioeconomically deprived. This highlights the likely influence of transportation diversity on social exclusion. Further consideration of the impacts of Hurricanes Irene and Sandy in NYC shows that people in areas with a lower transportation diversity were affected more and the transport inequity in these areas made it difficult to cope with these disasters and caused post-disaster social exclusion. Therefore, enhancing transportation diversity should support transport equity and reduce social exclusion under normal situations and during extreme events. The investigations conducted highlight the importance of the provision and distribution of all transportation modes, their influence on mobility during normal situations and extreme events and their contribution toward mitigating social exclusion. Finally, the collective results suggest that transportation diversity can contribute to more targeted and equitable transportation and community resilience planning, which should help decision-makers allocate scarce resources more effectively.
- Doctoral Dissertations