Giving catchment areas a reality check: Incorporating walkability into transport planning

Catchment areas have long been fundamental to public transport planning and evaluation, with a circular catchment area—or straight-line buffer approach—being the simplest. The assumption has been that people are willing to walk between 400 and 800 meters to reach a transit stop. By relying on a 400-meter radius around a public transport stop, however, it assumes that there is equal walking access throughout the radius, and the level of detail does not always consider factors that affect access to the public transport stop. Unsurprisingly, this method quickly falls short of reality – catchment areas need a reality check.

Using analysis tools and data

Circular catchment areas, calculated using the straight-line approach, have been shown to consistently overestimate population access to public transport stops and, thus, the walkability of the urban environment and the physical abilities of the person walking along the way. Instead, analysis tools and data can be used to better capture the complex context of the urban environment and better represent pedestrian access to transport stops:

• Geographic Information Systems (GIS) can be used in a high level of detail to refine circular catchment areas
• OpenStreetMap datasets can be used as it offer a representation of walking and bicycling.
• Isochrone maps can be used to correct walking distances by considering walking times

Incorporating the pedestrian environment

Catchment areas can be refined by incorporating the physical environment to incorporate the pedestrian environment. To start, incorporate key walkability information, such as:

• Existing footpath networks
• Detour information

Existing footpath networks

By incorporating existing footpath networks into catchment area analyses, public transport planners can better calculate real walking distances to transport stops. David Vale, for example, uses 83 transport stations in the Lisbon metropolitan area to show how pedestrian access compares to 700-meter circular catchment areas.

To calculate pedestrian access—or “pedestrian shed”—Vale used OpenStreetMap data and ArcGIS Network Analyst 10.2. Existing footpath networks were calculated for each site by

1. Removing non-pedestrian segments (highways, etc.)
2. Crossing-referencing Google Earth satellite imagery for accuracy

Pedestrian shed ratios of the 700-meter radii were calculated using ArcGIS Network Analyst 10.2. The resulting pedestrian sheds illustrate how much the physical environment impacts pedestrian accessibility to public transport and how insufficient theoretic catchment areas can be.

Detour information

Willingness to walk has been shown to sharply decline for trips longer than 400 meters. As such, more direct routes with smaller detour factors can increase willingness to walk to public transport. By incorporating walking detour information—which represents the time difference between walking a straight-line path and the actual distance someone must walk—into public transport planning, initial walking distances can be corrected. Detour factors can be calculated by dividing the actual distance by the straight-line distance. As a rule of thumb, detour factors should be as low as possible. Generally, between 1.0 to 1.25 is considered acceptable.

Isochrone maps also can be used to answer the question, “How far can someone walk to this transport stop in x amount of time?”. While ArcGIS tools can be used to produce isochrone maps, private companies, like EPB Schweiz AG, have developed pedestrian isochrone maps, making them much more accessible. These maps consider the physical context—such as topography and pedestrian shortcuts through parks—to more accurately show walking times.

Additional considerations

Beyond the physical environment, other variables significantly impact pedestrian access. Physical ability, safety, and security, as well as weather, for instance, all impact public transport access and should be considered in public transport planning as well. Physical abilities Walking times to public transport stops have as much to do with the physical environment as it does with the physical abilities of a person walking. Alves et al. summarize estimated walking speeds found in various studies, which show a range of estimated walking speeds across age groups:

• <30 years of age: 1.34 m/s
• >65 years of age: 0.60 – 1.00 m/s

For public transport to be accessible, walking speeds—and ranging human physical abilities—must be closely considered.

Safety and security Whether it is exposure to theft, harassment, unsafe driving behaviors, unsafe waiting areas, or fear of not knowing how to use the transport system, people consider such potential hazards when choosing to use public transport. When considering safety and security and pedestrian access to public transport stops in planning, Jehle et al. provide helpful criteria:

Security

o   Liveliness of streets o   Cleanliness and appearance o   Lighting o   Visibility of footpaths

Safety

o   Availability of footpaths o   Driver behaviors o   Joint footpath use by cyclists and pedestrians o   Pedestrian visibility

Weather

While weather may not always be shown to influence the decision to walk to public transport, it undoubtedly impacts the experience of walking of walking to public transport. Physical design choices can counter weather and improve walking experiences despite it Walk21’s top recommendation for achieving and integration of walking in public transport is to provide infrastructure to protect against weather conditions. The placement of such infrastructure should be a planning consideration to improve the experience of walking to public transport.

All footnotes below

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