Locating major passenger sources (MPS) and major passenger destination (MPD).

<p>(a) In the San Francisco URT network, the census tracts in yellow, orange, and red indicate the MPS passenger production values of the most vulnerable segment. The census tracts shown in shades of blue represent the segments' MPD passenger attraction values. Black links indicate the connections between each selected URT segment and its MPS. (b) In the Boston URT network, the census tracts in yellow, orange, and red indicate the MPS values of the most vulnerable segment. The census tracts shown in shades of blue represent the segments' MPD values. Black links indicate the connections between each selected URT segment and its MPS. (c) The color of each segment represents its number of MPS (). (d) The color of each segment represents its number of MPS (). (e) The distribution of the number of major sources of passengers in San Francisco. (f) The distribution of the number of major passenger destinations in San Francisco. (g) The distribution of the number of major sources of passengers in Boston. (h) The distribution of the number of major passenger destinations in Boston.