Accounting for uncertainty and variation in accessibility metrics for public transport sketch planning
Accessibility is increasingly used as a metric when evaluating changes to public transport systems. Transit travel times contain variation depending on when one departs relative to when a transit vehicle arrives, and how well transfers are coordinated given a particular timetable. In addition, there is necessarily uncertainty in the value of the accessibility metric during sketch planning processes, due to scenarios which are underspecified because detailed schedule information is not yet
... on is not yet available. is article presents a method to extend the concept of "reliable" accessibility to transit to address the first issue, and create confidence intervals and hypothesis tests to address the second. those values. We term this metric average instantaneous accessibility: instantaneous because the accessibility is calculated independently at each instant, and average because those values are averaged. Computing Accessibility Our method consists of several steps. We first compute travel times to all destinations, accounting for the uncertainty in proposed transit lines that have not yet received schedules. We then choose a travel time cutoff and a desired level of reliability for the accessibility metric. Finally, we evaluate uncertainty in our estimates using a bootstrapping process. is process is depicted visually in Figure 1 , and is described in the following sections.