A study of Seattle-area park-and-ride lots found that for suburban lots, 50% of
the park-and-ride facility’s demand is typically generated within a 2.5-mile (4-km)
radius of the facility, and that an additional 35% comes from an area defined by a
parabola extending 10 miles (16 km) upstream of the lot and having a long chord of
10 to 12 miles (16 to 19 km).(R28) This market area is illustrated in Exhibit 3-8(a).
I need to make a diagram that is an analogue of this for walking. The 'stair-steps' of distance decay, and their trip-generation potential. The half mile radius around transit stations is simply not the whole picture. It's an average, rather than a distribution. And if there is a big, nice pocket of density, just beyond the half-mile circle, it's not going to capture the full effects of transit station accessibility.