By Chris McCahill
As highlighted in two recent SSTI webinars in March and April of this year, accessibility measures are becoming more useful in practice. The most notable examples rely on proprietary data and methods, but open source approaches are also gaining traction, while highlighting the need for more reliable, open data.
Accessibility measures describe how easily people can reach destinations, usually in terms of travel time, given the existing transportation system and land use patterns.
Research published in a recent Transportation Research Record describes UrbanAccess, an open source accessibility tool developed at UC-Berkeley. Using several open data sources, it measures access to jobs by transit and walking. Like the commercial platform that we use often at SSTI, Sugar Access, this tool accounts for walk time, wait time, and in-vehicle time for transit trips, and it can incorporate travel time decay functions, which give more weight to nearby destinations than distant ones.
The tool uses transit networks from General Transit Feed Specification (GTFS) data, pedestrian networks from OpenStreetMap (OSM), and job locations from Longitudinal Employer-Household Dynamics (LEHD) data. Shortest path calculations are made using the open source Pandana tool.
More recently, PeopleForBikes announced their new Bike Network Analysis (BNA) tool, developed with Toole Design Group. The open source tool measures access to destinations by biking in roughly 300 U.S. cities using the Level of Traffic Stress (LTS) concept. Only low-stress facilities such as designated bike facilities and low-speed local roads are considered.
The BNA relies mainly on data from OSM, which means PeopleForBikes is also encouraging cities to add the relevant data wherever it’s missing or inaccurate. That includes information about roads, bike facilities, and points of interest (POIs), which can be particularly sparse.
Other tools include Conveyal’s Transport Analyst and the Conveyal-based MIT project CoAXs, which use GTFS and OSM data to produce travel sheds for accessibility analyses.
As PeopleForBikes staff writer Michael Anderson points out, these tools are only as good as the available data. GTFS is the go-to data for transit networks but the information may not reflect actual transit performance and many agencies don’t offer it publicly. Sugar Access overcomes some challenges by using commercial data from HERE (formerly Navteq), which include vehicle speeds and good POI coverage, but it also relies on GTFS and LEHD data.
Ultimately, the available tools and data let us do a lot more than we could just a decade ago. As the quality and coverage of data improves and as tools become more affordable and streamlined, accessibility measures will be integral to transportation-related decision making.
Join SSTI for our September 12 webinar to learn more about PeopleForBikes new BNA tool.
Chris McCahill is a Associate Researcher at SSTI.
Accessibility for all: Open source options for measuring access to destinations
By Chris McCahill