Access

MengyingCui.jpg
The Access theme is led by Dr. Mengying Cui. It aims to measure the ease of reaching destinations. 
Understanding access can help achieve the ’30-minute city.’

Accessibility measures the ease of reaching destinations and provides a way to evaluate the performance of transport system. ’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).

primal-access

To apply this in practice, the function of costs needs to be specified, and the most basic one is cumulative opportunity measure, written as,

cumulative-opportunity

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

Accessibility by public transport to jobs in Sydney, jobs within 30 minutes.

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.

newframeworkfcapaper
Full cost accessibility (FCA) framework

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.

full30min

Recent accessibility papers by TransportLab

2018

2017