I lay my subway lines along the most car and bus traffic congested routes. In the initial layout of the city, I try to reserve one corner of every street intersection for a bus and subway stop. I don't necessarily install them on initial layout, but I'll either leave the two parcels vacant, zone the block so that only single parcel structures can grow there, or place small parks on the location. That way if the corner develops skyscrapers, hence increasing demand, the bus and/or subway are ready for installation. Combining bus, subway, train, and monorail stations opposite or adjacent to one another integrates the transit system.
