Case Study:

Tren Urbano

Methodology

Station-Area Walkability

In addition to measuring regional accessibility, the MIT research team also evaluated station-area walkability for the Tren Urbano system. People are typically willing to walk no more than a quarter- to a half-mile to access a rail transit system, and the benefits largely accrue to land uses located within this area. If the street network is circuitous or other barriers to travel exist, the accessible land area may be smaller than the area within a given radius, and the number of uses that benefit may be reduced.

To describe station-area walkability, the authors developed a "Walkability Index" (WI) that is defined as the ratio of the area of the observed transit impact zone (e.g., the land within an actual quarter-mile walking distance) to the area of the expected impact zone (e.g., a circle of quarter-mile radius). For a station that has no pedestrian access, the index is zero; for perfect pedestrian access (e.g., open land where the pedestrian can walk anywhere), the value is one. For a standard grid system, the index value is 0.6.

The authors measured the walkability of each station area using Census TIGER/Line files and GIS analysis tools. While the TIGER/Line files do not contain every piece of information relevant to walkability (e.g., sidewalks or pedestrian bridges), they do represent well the physical layout of the street network. Some cities or metropolitan areas have developed their own GIS file of the street network, which could also be used for this analysis.

To conduct the walkability analysis, a GIS package with network analysis capabilities, such as ArcInfo or TransCad, is required. The GIS is used to trace the street network within a quarter- to half-mile network distance of the station. Then, a buffer is drawn around these lines to represent the land area that is reachable within this walking distance. The buffer can be selected based on local characteristics. For example, in the Tren Urbano analysis area, a typical city block is 100 meters deep, so a buffer depth of 50 meters, or half this distance, was selected.

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