Robust accessibility: Measuring accessibility based on travelers’ heterogeneous responses to travel time uncertainty

New paper: Lee, J. and Miller, H.J. (2020) “Robust accessibility: Measuring accessibility based on travelers’ heterogeneous strategies for managing travel time uncertainty,” Journal of Transport Geography, 86, 102747.

Highlights

  • We develop an analytical framework for measuring accessibility considering travelers’ heterogeneous safety margin plans and routing strategies under travel time uncertainty.
  • We explore how accessibility changes under various safety margin plans and routing strategies.
  • We define and measure robust accessibility: geographic areas that are accessible regardless of the safety margin planning and routing strategy.
  • Robust accessibility provides a conservative and reasonable view of accessibility under travel time uncertainty.
  • We apply our framework to measure the accessibility impacts of new public transit service under travel time uncertainty.

Abstract

Uncertainties in travel times due to traffic congestion and delay are risks for drivers and public transit users. To avoid undesired consequences such as losing jobs or missing medical appointments, people can manage the risks of missing on-time arrivals to destinations using different strategies, including leaving earlier to create a safety margin and choosing routes that have more reliable rather than fastest travel times. This research develops a general analytical framework for measuring accessibility considering automobile or public transit travelers’ heterogeneous strategies for dealing with travel time uncertainty. To represent different safety margin plans, we use effective travel time (expected time + safety margin), given specified on-time arrival probabilities. Heterogeneity in routing strategy is addressed using different Pareto-optimal routes with two main criteria: faster travel time vs. higher reliability. Based on various safety margin and routing strategy combinations, we examine how accessibility changes under varying safety margin plans and routing strategies. Also, we define and measure robust accessibility: geographic regions that are accessible regardless of the safety margin planning and routing strategy. Robust accessibility can provide a conservative and reasonable view of accessibility under travel time uncertainty. To demonstrate the applicability of the methods, we carry out an empirical study on measuring the impacts of new transit service on healthcare accessibility in a deprived neighborhood in Columbus, Ohio, USA.

Measuring risk of missing transfers in public transit systems using high-resolution schedule and real-time bus location data

New paper: Liu, L. and Miller, H.J. (2020) “Measuring risk of missing transfers in public transit systems using high-resolution schedule and real-time bus location data,” Urban Studies  (Special issue on Big Data in the City)  https://doi.org/10.1177/0042098020919323

Abstract: The emergence of urban Big Data creates new opportunities for a deeper understanding of transportation within cities, revealing patterns and dynamics that were previously hidden. Public transit agencies are collecting and publishing high-resolution schedule and real-time vehicle location data to help users schedule trips and navigate the system. We can use these data to generate new insights into public transit delays, a major source of user dissatisfaction. Leveraging open General Transit Feed Specification (GTFS) and administrative Automatic Passenger Counter (APC) data, we develop two measures to assess the risk of missing bus route transfers and the consequent time penalties due to delays. Risk of Missing Transfers (RoMT) measures the empirical probability of missed transfers, and Average Total Time Penalty (ATTP) shows overall time loss compared to the schedule. We apply these measures to data from the Central Ohio Transit Authority (COTA), a public transit agency serving the Columbus, Ohio, USA metropolitan area. We aggregate, visualise and analyse these measures at different spatial and temporal resolutions, revealing patterns that demonstrate the heterogeneous impacts of bus delays. We also simulate the impacts of dedicated bus lanes reducing missing risk and time penalties. Results demonstrate the effectiveness of measures based on high-resolution schedule and real-time vehicle location data to assess the impacts of delays and to guide planning and decision making that can improve on-time performance.

Keywords:  automatic passenger counter data, General Transit Feed Specification data, public transit, risk of missing transfer

NASEM Mapping Science Committee webinar: Geospatial Needs for a Pandemic-Resilient World. 

Epidemics and pandemics such as the COVID-19 outbreak have clear geographic dimensions due to the vector spreading the virus (human contact), demographics and co-morbidity factors that vary geographically, the distributed and heterogeneous nature of health care systems, and the highly variable response and interventions from political authorities and the public-at-large. The decline and shifts in human activity also affect broader social, economic and environmental systems to varying degrees. Geospatial information can play vital roles in crafting effective government and societal responses at the operational, tactical and strategic levels.

On 17 June 2020, the Mapping Science Committee of the National Academies of Science, Engineering and Medicine will host an online workshop on Geospatial Needs for a Pandemic-Resilient World.  This workshop will explore the needs of federal agencies, organizations, and scientists for geospatial data science to understand and respond to epidemics/pandemics and developing infrastructure and policies that facilitate effective management and graceful recovery from these types of shocks.  This workshop is free and open to the public.