Measuring the geometric and semantic similarity of space–time prisms using temporal signatures

New publication: Miller, H.J., Jaegal, Y. and Raubal, M. (2019) “Measuring the geometric and semantic similarity of space-time prisms using temporal signatures,” Annals of the American Association of Geographers, 109, 730-753.

Well-established techniques exist for measuring the similarity of space–time paths. These measures support clustering and aggregation of space–time paths as well as moving objects database queries based on similar movement patterns or semantics. Little attention has been paid, however, to the analogous problem of measuring space–time prism (STP) similarity, despite comparable applications. This article presents and evaluates a method for measuring STP similarity through dimensionality reduction that leverages their inherent temporal ordering. The technique sweeps an STP along the time axis and derives one-dimensional temporal signatures based on a measured STP property that captures its geometry or semantics. These temporal signatures can be visualized directly as curves. We can also apply existing space–time path similarity measures to these signatures. To demonstrate the feasibility of this approach, we perform two sets of experiments measuring geometric and semantic similarity among STPs and assess the information within these curves using visualization, Fréchet distances, and clustering techniques. Results suggest that the temporal signature curves capture meaningful similarities and differences among STPs.

Accessibility planning in American metropolitan areas: Are we there yet?

Proffitt, D., Bartholomew, K., Ewing, R. and Miller, H.J. (2019) “Accessibility planning in American metropolitan areas: Are we there yet?Urban Studies, 56, 167-192.

Abstract.  Transportation-planning researchers have long argued that the end goal of a transportation system is increasing accessibility, or opportunities for individuals to meet their daily needs, but that US practice tends to focus on increasing mobility, or opportunities to travel farther and faster. This study finds evidence that the gap between theory and practice may be closing when it comes to accessibility, but that significant barriers still exist to the wider adoption of the accessibility paradigm among metropolitan planning organisations, the main entities responsible for regional transportation planning in the USA. We measure this gap by creating an accessibility index based on content analysis of a nationally representative sample of 42 US regional transportation plans (RTPs). We then use regression-tree analysis to determine the characteristics of metropolitan areas that are most likely to employ accessibility concepts. Finally, we identify barriers to a wider adoption of the accessibility paradigm. Most RTPs include accessibility-related goals, but few define the term or use accessibility-oriented performance measures. The lack of clarity on accessibility leaves vehicle speed as the fundamental criterion for success in most plans. Our analysis finds that MPOs serving large regions with high per capita income are the most likely to produce plans that focus on accessibility. We argue that such places produce more accessibility-oriented RTPs because they have greater planning capacity and recommend changes to federal planning guidelines that could speed the adoption of the accessibility paradigm in RTPs.

New publication: Accessibility with time and resource constraints

Mahmoudi, M., Song, Y., Miller, H.J. and Zhou, X.  (2019) “Accessibility with time and resource constraints: Computing hyper-prisms for sustainable transportation planning,” Computers, Environment and Urban Systems, 73, 171-183


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