New publication: Accessibility with time and resource constraints

Mahmoudi, M., Song, Y., Miller, H.J. and Zhou, X.  (in press) “Accessibility with time and resource constraints: Computing hyper-prisms for sustainable transportation planning,” Computers, Environment and Urban Systems.


Accessibility is the ease of obtaining desired destinations, activities, or services in an environment. A common accessibility measure in basic and applied transportation science is the space-time prism (STP) and the network-time prisms (NTPs): these are the envelopes of all possible paths between two locations and times in planar space and transportation networks, respectively. STPs and NTPs focus on time as the scarce resource limiting accessibility. However, other resource constraints can constrain space-time accessibility, such as limits or “budgets” for energy, emissions, or monetary expenses. This paper extends NTPs to include other resource constraints in addition to time. Network-based resource hyper-prisms (RHPs) incorporate other resource constraints into NTP, capturing the trade-offs between time and other resources in determining space-time accessibility. We conceptualize RHPs as a constrained optimization problem and develop a forward and backward resource-dependent time-dependent dynamic programming to determine the boundaries of a RHP given time and other resource budgets. We illustrate our approach using the Chicago sketch network (with 933 nodes and 2967 links) for the use case of an individual with an internal combustion engine vehicle and a carbon emission budget and using portions of Washington, D.C. and Baltimore networks (with 12,145 nodes and 30,697 links) for the use case of siting electric vehicle charging stations to maximize regional accessibility.


Resource hyper-prisms; Space-time prisms; Accessibility; Sustainable transportation; Dynamic programming

Opioid Innovation Fund – Franklin County Opioid Crisis Activity Levels (FOCAL) map

OSU’s Opioid Innovation Fund is supporting CURA’s project, the Franklin County Opioid Crisis Activity Levels (FOCAL) map. We will be building mapping and spatial analysis tools to understand the social factors associated with opioid overdoses and barriers to effective treatment.  This campus-community partnership involves Harvey Miller (CURA), Ayaz Hyder (College of Public Health), Lauren Southerland (OSU Wexner Medical Center). David All (WellHQ), Gretchen Hammond (Mighty Crow Media) and Sherri Kovach (Central Ohio Trauma System).


Measuring the impacts of new public transit services on space-time accessibility

Lee, J. and Miller, H. J. (2018) “Measuring the impacts of new public transit services on space-time accessibility: An analysis of transit system redesign and new bus rapid transit in Columbus, Ohio, USA,” Applied Geography, 93, 47-63.


  • Lack of access to opportunities contributes to poor social and health outcomes.
  • Columbus, OH introduced a transit route and schedule redesign and bus rapid transit.
  • We analyze impacts on accessibility to opportunities in a deprived neighborhood.
  • Detailed route and schedule data allow high resolution accessibility analysis.
  • The new bus rapid transit has a much greater impact on accessibility


The absence of effective access to opportunities and services is a key contributor to poor socio-economic and health outcomes in underserved neighborhoods in many cities. The city of Columbus, Ohio, USA is attempting to enhance residents’ accessibility by providing new public transit services. These new services include a major Transit System Redesign (TSR) of the conventional bus network and the introduction of a new bus rapid transit, named CMAX. Using a high-resolution space-time accessibility measure, we analyze whether these new public transit services will change residents’ accessibility to job and healthcare in an underserved neighborhood of Columbus. Also, we assess whether enhancing the CMAX service to reduce delays (e.g., reserved lane, off-board payment system) will improve accessibility. The high-resolution space-time accessibility measure in this study uses published public transit schedules via the General Transit Feed Specification (GTFS). We use multiple departure times during a day to account for the temporal fluctuations of accessibility based on the transit schedule changes. We also consider the operating hours of job opportunities and healthcare services. Results suggest that the TSR yields ambiguous benefits for accessibility to jobs and healthcare. However, the new CMAX service and its potential upgrades lead to a substantial increase in both job and healthcare accessibility. The results can be used for city officials and urban planners to evaluate the effectiveness of public transit innovations in improving accessibility.

Keywords: Transportation; Space-time accessibility; Public transit; Bus rapid transit; Jobs; Healthcare