Access

Accessibility measures the ease of reaching destinations and provides a way to evaluate the performance of transport system. The ’30-minutes city’, proposed by Greater Sydney Commission, suggests that that 75% of the people should be able to reach jobs within 30 minutes using transit.

Accessibility has numerous dimensions, considering where, when, what, and how accessibility is measured for whom by what traffic mode based on how much travel cost is taken.

• Where: where accessibility is being measured, a block in downtown, suburban, or exurban area?
• When: when accessibility is being measured, during peak hours or non-peak hours, day time or night time?
• What: what is being accessed, e.g., jobs, schools, shoppings, restaurants, parks, hospitals?
• How: methods to measure accessibility, e.g., primal, dual, place rank, or utility-based accessibility measures.
• For whom: for whom accessibility is being measured, individual persons or a group of individuals aggregated spatially?
• What mode: what mode is being used to access, on foot, by bike, transit, or automobile?
• How much: how much travel cost is being spent to access, measured by travel distance, travel time, or full cost of travel?

Primal Accessibility

Primal accessibility as presented here is a generalization of the first accessibility formulation by Hansen in 1959. In the primal accessibility (A) problem, we solve for how many destinations (O) can be reached in t minutes from origin i by activity type or purpose (z), and population subgroup (p) (income category, racial group, modal availability, etc.), with a given mode (m), at a time of day (h),  considering costs (c):

To apply this in practice, the cost function needs to be specified, for instance the  cumulative opportunity measure is written as:

Accordingly, the following map shows the primal accessibility to jobs in 30 minutes using public transit in Sydney at morning peak hours.

Full Cost Accessibility

Generally, accessibility is measured from the perspective of travel time, only considering the time cost, as travel time is a determinant factor for travelers’ choice of mode, route, or departure time, while it neglects other internal cost factors, like safety cost and vehicle operation cost, as well as the external costs of travel. Full cost accessibility, instead, extend accessibility analysis to incorporate the full cost of travel, which allows us to  evaluate accessibility across different cost aspects.  The framework of full cost accessibility defines the internal and external cost of travel, proposes the new path types, and applies the primal accessibility for accessibility evaluations.

Accordingly, the following map shows the full cost accessibility to jobs in $9.15 full cost threshold (equal to 30 minutes time threshold at $18.30/h value of time) by auto in Minneapolis – St. Paul metropolitan area at the morning peak hours.

Recent accessibility papers by TransportLab

• Borowski, Elisa, Ermagun, Alireza, and Levinson, D. (2018) Disparity of Access: Variations in Transit Service by Race, Ethnicity, Income, and Auto Availability.
• Chaloux, Nick,  Boisjoly, Genevieve,  Grise, Emily, El-Geneidy, Ahmed, and  Levinson,  D. (2018) I only get some satisfaction: Introducing satisfaction into measures of accessibility.
• Sarkar, Somwrita, Wu, Hao and Levinson, D. (2018) Measuring polycentricity via network flows, spatial interaction, and percolation.
• Wu, Hao and Levinson, D. (2018) Optimum Stop Spacing for Accessibility.
• Wu, Hao and Levinson, D. (2018) Effects of Timetable Change on Job Accessibility.
• Wu, Hao and Levinson, D. (2018) Commute Mode Share and Access to Jobs across US Metropolitan Areas.

2018

• Palmateer, Chelsey, Ermagun, Alireza, Owen, Andrew, and Levinson, D. (2018) Accessibility-based Evaluation of Transit Projects(*) (Working Paper).
• Palmateer, Chelsey, Ermagun, Alireza, Owen, Andrew, and Levinson, D. (2018) The Role of Transit Service Area Definition in Accessibility-based Evaluation (*) (Working Paper).
• Palmateer, Chelsey and Levinson, D. (2018) Justice, Exclusion, and Equity: An Analysis of 48 U.S. Metropolitan Areas.(*) Presented at  Smart Cities – Governing Accessibility, Air Pollution and Equity at the University of São Paulo, Brazil, August 24-25, 2017
• Cui, Mengying and Levinson, D. (2018) Full cost accessibility. Journal of Transport and Land Use.  11(1) pp. 661-679

2017

• Cui, Mengying and Levinson, D. (2017) The Safest Path: Analyzing the Effects of Crash Costs on Route Choice and Accessibility  Presented at the Transportation Research Board Annual Meeting 2017.

• Iacono, Michael, Cao, Jason X., Cui, Mengying and Levinson, D. (2017) Intraurban Accessibility and Employment Density. Presented at the Transportation Research Board Annual Meeting 2017.