an alternate plan was put forth by john hencken, an engineer, and approved by ernest p. goodrich, consulting engineer to the regional plan of new york and its environs. a linear corridor would be built from the battery to yonkers. a freight railroad would lie underground. on ground level would be roads alongside the corridor and an indoor enclosed sidewalk. the mezzanine, between the first and second floors, would be occupied by office space. the second floor would carry a "continuous noiseless moving platform system for passenger service", with adjacent belts moving at various speeds, for a maximum of 21 miles per hour (34 km/h) in the middle. this service would be free, and would be a substitute for new subways in the corridor. above the second floor would be about ten stories of apartments, offices, businesses, and other uses appropriate for the neighborhoods; these would be the main source of revenue to pay for the project. a high-speed motor parkway, open to passenger cars only, would lie on top. cars would reach the upper level via ramps at both ends and elevators at convenient intervals.