732,754. Push-button lifts. OTIS ELEVATOR CO. Aug. 4, 1953 [Aug. 13, 1952], No. 21497/53. Drawings to Specification. Class 78 (3). A control system for a plurality of elevator cars serving a plurality of landings, including terminal landings, in which call registering means are provided for each of the landings, is provided with means responsive to intermittent traffic conditions for causing operation of one or more of the cars on an intermittent basis, and means responsive to greater traffic conditions for changing over the operation to cause the cars to be despatched from at least one of the terminal landings on a time basis. The invention is described in connection with a four car system serving ten floors and in which the cars may be operated either with or without attendants. On " without attendant " operation the cars may be operated on " on call " operation or " continuous call " operation. The cars are despatched on their upward and downward trips on both " with attendant " operation and on " without attendant continuous call " operation. The despatching on " with attendant " operation is effected by giving despatching signals to the cars whereupon the attendants start the cars. On " without attendant " operation, the despatching is effected by automatically starting the cars. On " without attendant " operation the system operates " on call " until service demand conditions dictate the switch-over to " continuous call " operation. On " on call " operation, a middle free car parks at a selected middle parking floor, e.g. the sixth floor, an active bottom car parks at the bottom terminal and, the other two cars park as inactive cars, one at the top terminal and one at the bottom terminal. The cars park with the landing doors and cars doors closed. Upon the registration of a landing call for a floor above the lower terminal other than the floor at which the middle free car is parked, the middle free car is started in a direction towards that floor and upon arrival thereat is brought to a stop and its doors automatically open. The intending passenger enters the car and presses the car button for his destination. The doors close and the car takes the passenger to his destination where it is brought to a stop and the doors open, permitting the passenger to leave the car. If other calls are registered, the car stops at each floor for which car calls are registered and for which landing calls for the direction in which the car is set to travel are registered. It continues to travel in the same direction after each stop until it stops at the furthest floor in that direction for which a call is registered. This may be a landing call for the opposite direction. When all calls are responded to, the car automatically returns to the middle parking floor. If while the car is on its way to the parking floor a landing call is registered for a floor beyond, the car passes the parking floor and proceeds to the floor of call. The active bottom car serves incoming traffic. When it is started in the up direction in response to a car call, it assists the middle free car in answering landing calls. If the car does not reach a certain floor, it returns to the bottom terminal as the active bottom car upon answering its higher call, responding to calls on the way down. If on its upward trip it does pass a predetermined floor, it becomes the new middle free car and the previously middle free car is returned to the bottom terminal. A new active bottom car is selected, usually the inactive bottom car. A changeover is also effected when the middle free car is returned to the bottom terminal. In such event, the active bottom car becomes the new middle free car and goes to the middle parking floor and either the previous middle free car or the inactive bottom car becomes the new active bottom car. Should a car fail to response within a certain time interval, it is removed from service and another car is caused to take its place. This failure may be manifested in failure to start in response to a call for another floor or failure to open its doors in response to touching a button at the landing where parked. In the case of the middle free car, the active bottom car becomes the new middle free car and the inactive bottom car becomes the new active bottom car. In the case of the active bottom car, the inactive bottom car becomes the new active bottom car. Should in either case the car, which should take the place of the car'which failed to response, fail to do so, another car is called to take the place of the car which failed to response. Upon the registration of one or more overlapping landing calls for a certain period of time the system is automatically switched over to " continuous call " operation. Also this time period is shortened in accordance with the number of landing calls in registration. In addition, the change-over is effected in response to the automatic load non-stop operation of a car, providing a landing call is in registration. When the system is switched over to " continuous call operation, the cars are selected for despatching in the order of their arrival at the terminals. The despatching operation occur at the expiration of given time intervals. When the interval expires the doors close automatically and the selected car starts on its trip to the opposite terminal. When on " continuous call " operation, the despatching interval is adjusted automatically in accordance with whether the cars are early or late on a round trip basis. If traffic increases so as to slow the cars, the interval is gradually increased and, as soon as traffic decreases, the interval is shortened. Also, the despatching interval may be automatically adjusted in accordance with the number of cars in service. Under " continuous call operation, when all landing calls have been responded to for a certain interval of time, the system automatically changes back to " on call " operation. When this occurs, all cars not at the bottom terminal are started to return thereto. The car at the bottom terminal or the first car to arrive there is caused to become the middle free car and goes to the middle parking floor. When this car leaves the bottom terminal, another car there or the next car to arrive there is selected as the active bottom car and remains at that floor. When the active bottom car is selected, one of the two remaining cars is selected to go to the top terminal as the inactive top car and the other car proceeds to the bottom terminal and becomes the inactive bottom car. The invention is stated to be applicable to installations having basement service in which case the active bottom car would serve the basement. In addition, late car reversal operation may be provided when operating under despatching, as for example as disclosed in U.S.A. Specification 2,589,242. Should no car start within the time interval after the last to run car stops, the despatching circuits are disconnected enabling the cars to run freely in response to landing calls. The system may be arranged so that the cars do not have to proceed to the bottom terminal to be selected upon changing over from "continuous call to " on call "operation.