Access is a necessary-but-not-sufficient condition for strong ridership: It’s possible that a transit system offering improved access might still show a drop in ridership — say, because of a spate of equipment breakdowns — but a drop in access implies that ridership will eventually fall as well, because longer trips inevitably make alternative modes more attractive…

The idea of transit access isn’t new, but our ability to put a useful number on it is. David Levinson, a professor at the University of Sydney who has written numerous books about transportation access, says that quantitative breakthroughs now allow planners to make far more precise calculations than before. “We’ve got better data now through the General Transit Feed Specification and GPS, as well as from Census Bureau datasets. For each person, the data tells which block they live in and which block they work in. This didn’t exist at that detailed a level until the mid-2000s.”
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