The Value of Contiguous Grouping within Destination Dispatching 1

The Value of Contiguous Grouping within Destination Dispatching

Overview
This article briefly illustrates the role of elevator dispatching within an elevator system. It then describes the difference between traditional elevator systems and the destination dispatching approach and explains that destination dispatching directs specific passengers into specific elevators. The article then explores the reasons that contiguous grouping, the grouping of passengers going to contiguous or nearly contiguous floors into the same elevator, provides better elevator service than using non-contiguous grouping.
Elevator Dispatching
In order to most effectively serve the riding public, modern elevator systems use proprietary elevator dispatching algorithms, often referred to collectively as the elevator dispatcher, to determine which car in a group of elevators should respond to a specific demand for service. The dispatcher chooses a particular car to serve a particular request in a way that supports providing the best overall elevator service to all of its users. The dispatcher may consider, among other objectives, how long people wait in the hallway, how long people spend in the elevator and how much energy the system is consuming.
Consider this example: A passenger is waiting for an elevator at floor 3 to take him up to a higher floor in a 12-story building, and there are three elevators capable of serving this passenger. The elevator dispatcher must select which one of the three elevators to assign to this service request. If the first elevator is traveling down to the lobby and is already filled with passengers and the second car is at floor 8 traveling up to drop off two passengers at floors 9 and 10 and the third car is empty at floor 2, then the dispatcher has an easy decision to make – the empty car is probably the best choice.
But the situation is usually more complex than the simple situation described above. Elevator dispatchers must be designed to balance existing known situations (e.g. where is each car currently positioned), existing unknown situations (e.g. how many people are waiting in the hall way for this car) and future unknown situations (e.g. how many people will arrive at floor 10, wanting to travel down, in the next few seconds?) and select the appropriate car that can serve a specific service request in an appropriate amount of time without disrupting overall efficiency of the system. Elevator companies spend significant resources to develop the best dispatching algorithms possible to handle these complicated scenarios.
Elevator dispatchers must provide good service for all passengers. It is not acceptable for an elevator dispatcher to allow some passengers to wait for a very long time while serving other passengers extremely quickly even though this approach might produce acceptable “average” response times. This type of dispatching methodology will result in unhappy long-waiting passengers and complaints of poor elevator service. Instead dispatchers must balance the requests of all passengers at all locations to make sure that no passenger waits too long or spends too much time in the elevator.

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