Phase III – Accessibility Calculator

Accessibility is affected by travel time, travel cost, and the locations and service hours of desired destinations, as well as the person’s knowledge of and comfort with the choices of travel modes and service providers. Planning for accessibility is important for making sure that those who require public transit will have good access to jobs and services such as shopping and health care.

There are three primary types of accessibility measures:

· Access measures: the cost of access to the nearest service point in the network
· Threshold measures: the ability to reach a desired destination within a time, distance, or cost limit
· Continuous measures: the attractiveness of residences based on their accessibility to jobs and services

A major indicator of transportation equity is accessibility, namely the ease with which residents can reach key opportunities such as employment, schools, health care, etc. It is the primary measure of transportation’s capability to move people and goods. Typically measured in terms of number of activities within a certain travel time or as a weighted sum of all activities discounted by the difficulty in reaching them, conventional TAZ-based regional travel models lack the sensitivity to link these measures to particular population subgroups (due to TAZ aggregations).

With new GIS-based tools, such as the TransCAD model being used by the BREJT project team, it becomes possible to sharpen the analysis to units of individual households or neighborhoods, defined by particular characteristics. Drawing upon Census data and/or household travel survey data, target populations are identified by location and their travel opportunities quantified using an “Accessibility Calculator” tool which we will develop. Essentially this tool will be an analytic procedure designed to run with TransCAD that will compute an estimate of the number of particular types of opportunities available from a given origin either within a given travel time range (say 30 minutes) by highway or transit, or as a total number of such opportunities discounted by respective travel time/cost. One may then either evaluate accessibility or accessibility changes for a given community, or sum up the values across many communities with similar characteristics.

This tool can subsequently be applied to any project or planning scenario to obtain an instant and credible measure of how specific population groups would gain or lose compared to current conditions or alternative approaches. This will be a key measure of impact in the TERP-supported regional case study, but will be available for use in any of the other case studies in the BREJT project, and would be a recommended Toolkit measure for use in evaluating regional transportation plans or project funding programs.