3.2. Public transit that extends to the suburbs
The ‘‘drive-and-ride’’ model of Section 3.1 is based on the
assumption that all suburban commuters use roads and public
transit sequentially on every trip. But what about extending
public transit service to the periphery? In that case, some
suburban commuters, would choose public transit while others
would continue to drive-and ride. This is a modification of the
model of Section 2. The planner’s optimization problem is now
written as follows where n 22 is the suburban population of public
transit riders and k i the public transit investment in area i: