Probably you could just bunch census tracts within a certain distance of any stop and count them as being part of their nearest stop and then average them. (We

Probably you could just bunch census tracts within a certain distance of any stop and count them as being part of their nearest stop and then average them. (Weighing correctly for population differences.) If you wanted to do it better, you could have the weight for each census tract fall off with distance from the stop.