upper section of shaft i after leading cab v exits zone 21 cab v can continue to move down shaft i and service passengers in the middle section of shaft i step 10 after sensors in zone 30 indicate that leading cab v has exited zone 30 trailing cab u can move down shaft 1 and enter zone 30 where it can load down passengers after sensors in zone a 1 indicate that cab u has exited zone a 1 new trailing cab t can move down into zone a 1 and wait step 11 after sensors in zone 21 indicate that leading cab v has exited zone 21 trailing cab u can move down shaft i and service passengers in the upper section of shaft i after sensors in zone 30 indicate that cab u has exited zone 30 trailing cab t can move down into zone 30 and load down passengers step 12 at this approximate point in time cabs n o and p in shaft iii can begin to execute the aforementioned steps 1 through 6 in shaft iii and cabs q r and s in shaft ii can begin to execute the aforementioned steps 8 through 11 in shaft ii step 13 after sensors in zone 11 of shaft i indicate that leading cab v has exited zone 11 trailing cab u can move down shaft i into zone 20 and service passengers in the middle section of shaft i after sensors in zone 21 indicate that cab u has exited zone 21 trailing cab t can move down shaft i into zone 29 and service passengers in the upper section of shaft i step 14 after leading cab.