What’s a Transit “Walk Shed”?
Metro will soon be measuring how much growth happens in places that are walkable to transit. Here’s an in-depth look at how we define “walkable” to Metrorail stations and Metrobus stops.
Metro’s new Connecting Communities metric will measure annual household growth in our region that occurs within the “transit shed” – the catchment area around transit service that generates walk ridership. And improving walkability can be an incredibly cost-effective way to reduce congestion and increase transit ridership. Let’s take a closer look at how we defined what’s “walkable to transit.”
How Far is Walkable? First, we defined walking distance as a half-mile from Metrorail, and a quarter-mile from Metrobus, for a number of reasons:
- Of all the passengers who walk to Metrorail each morning, the median walking distance is just under a half-mile (0.35 miles, actually). Riders walk farther to some stations than others, but the systemwide average is just shy of a half-mile. Since rail riders are on average willing to walk a little under a half-mile today, it is reasonable to use a half-mile as an upper limit for walking in the future. (We don’t have similar survey data on Metrobus – yet.)
- The land use within a quarter- and half-mile is where we see the strongest effects on ridership on Metro today. More on this below.
- Academic literature supports the half-mile radius from rail transit as no better than any other distance, particularly for the link between households and ridership.
- Practically, setting the distance any farther than 0.50 and 0.25 miles increases overlap with other nearby stations and bus stops, which increases computational complexity.
Walking Along a Network. While it’s easy to compute a catchment area “as the crow flies,” this fails to account for barriers like highways and rivers, and variations in street layout – which can be significant in our region. So, we constructed walkable areas using Network Analyst in GIS, based on an OpenStreetMap street network file. We found that OpenStreetMap’s network represented well some pedestrian-specific infrastructure like paths, trails, and overpasses – more so than other networks built primarily for routing automobiles.
We modified the OpenStreetMap network somewhat to more accurately represent what’s “walkable” – removing freeways and interstates, adding short pathways at rail stations with multiple exits, and more. The resulting catchment areas are not perfect – not every pedestrian link is represented, and not all links on the road network are pedestrian-friendly, so we will be improving the network in the future.
Nevertheless, this network analysis captured the major impacts on walkability from barriers, rivers, and street grid. For example, look at the impact of the network analysis at two sample Metrorail stations below:
Why Does This Matter? Because Metro wants to understand how well it connects communities in our region, and the land use around transit is a huge determinant of ridership and Metro’s success. Preliminary research at Metro suggests that the number of households within a Metrorail station’s walkable area can explain over 90% of the station’s AM Peak walk ridership.
Note 6/18/2014: thanks to some eagle-eyed commenters, we realized that there were some errors in the originally-published diagram above, undercounting the walkable area from several stations. We have since corrected the diagram.
What’s Next: We will use these sheds to measure growth near Metrorail and Metrobus for the Connecting Communities metric, and to explore the connection between adjacent land uses and rail ridership.