Choosing a passenger lift is not simply a matter of deciding how many people will fit inside the car.
The more important question is how the lift will cope with the way people actually move through the building.
A six-storey office with several hundred people arriving within a short period each morning presents a very different challenge from a residential building with a similar number of occupants. A hotel introduces another pattern altogether, with guests, housekeeping staff, luggage and service movements occurring at different times.
Lift traffic analysis looks at these patterns before the lift arrangement is finalised. It helps establish whether the proposed number, size and performance of the lifts are appropriate for the building rather than relying on capacity alone.
What Does Lift Traffic Analysis Look At?
At its simplest, lift traffic analysis considers the demand that will be placed on a lift or group of lifts.
That means looking beyond the maximum number of people expected to occupy the building.
Factors can include:
- Building population
- Number of floors served
- Expected passenger numbers at busy periods
- Where passengers enter and leave the building
- Lift capacity
- Travel speed
- Door operation
- Journey and stopping patterns
- The number of lifts available
- The type and use of the building
The purpose is to understand what happens when several people want to use the lifts within the same period.
A lift may have enough capacity to carry ten or twelve passengers on an individual journey, for example, but that tells us very little about how effectively it can move hundreds of people between floors over a busy 15 or 30-minute period.
Building Population Is Only the Starting Point
Occupancy is clearly important when specifying commercial lifts, but two buildings with the same population can place completely different demands on their lifts.
Consider an office and a hotel, each accommodating 400 people.
In the office, a large proportion of those people may arrive between 8.30am and 9.00am and travel from the main entrance to their respective floors. At lunchtime, movement may increase in both directions before reversing again towards the end of the working day.
The hotel is unlikely to operate in the same way. Guests arrive and leave throughout the day. Breakfast and check-out can create busier periods, while housekeeping, room service, luggage and other hotel operations introduce additional journeys.
The population figure might be identical. The traffic pattern isn’t.
This is why occupancy numbers should not be used in isolation to decide how many lifts a building needs.
Peak Traffic Can Determine the Lift Requirement
The busiest period of the day is often more useful than average usage.
If 600 people use a lift installation over an entire working day, the system may appear to have a relatively modest workload. If 150 of them want to travel within the same short period, the design problem changes considerably.
Office buildings provide a straightforward example.
Morning arrival can create predominantly upward traffic from the main entrance. At lunchtime, passengers may be travelling both up and down. At the end of the day, the dominant flow can become downward.
The lift arrangement needs to cope with these periods without creating unreasonable queues or making occupants wait through repeated journeys before they can enter a car.
Average daily passenger numbers can hide this problem.
Lift Capacity Does Not Tell the Whole Story
A larger lift can carry more people on each journey, but increasing car capacity does not automatically solve a traffic problem.
The complete journey has to be considered.
Passengers need to enter the car, select floors, travel, stop at intermediate landings, leave the lift and allow other passengers to enter. The lift then has to return or continue to another call.
Every stop adds time.
A large lift stopping at several floors may therefore handle passengers differently from two smaller lifts working together.
Door arrangements also matter. The time taken for doors to open and close and for passengers to enter or leave contributes to the overall journey cycle.
This is why simply choosing the largest available lift car is not the same as designing an efficient lift arrangement.
The Number of Floors Changes the Calculation
A lift serving two or three floors has a very different working pattern from one serving ten or fifteen.
As the number of floors increases, there are more possible destinations and potentially more stops during each journey.
Travel distance increases too.
The relationship between building height, passenger demand, lift speed and car capacity therefore needs to be considered together.
A faster lift may reduce travel time between floors, but speed alone cannot remove delays caused by repeated stops, door operation or passengers waiting to enter and leave.
For lower-rise buildings, very high travel speed may offer little practical benefit because so much of the journey cycle occurs at the landings rather than between them.
When Does a Building Need More Than One Lift?
There isn’t a single occupancy figure at which every building suddenly requires two lifts.
The decision depends on how the building operates.
A second lift can increase passenger handling capacity, but there are other reasons why multiple lifts may be considered.
Resilience is one.
Every lift requires periods of planned lift maintenance, and faults can occasionally take equipment out of service. If a building relies entirely on one lift, vertical access may be significantly affected while that lift is unavailable.
This becomes particularly important where occupants depend on the lift to access the building.
Multiple lifts can also work together rather than operating as completely independent systems. Suitable controls can allocate calls between cars so that unnecessary journeys are reduced and passenger demand is distributed more effectively.
The question is therefore not simply, “Can one lift carry everyone?”
It is whether one lift can provide the required level of service throughout the building’s working day.
Different Buildings Produce Different Traffic Patterns
There is no universal traffic model that suits every building.
Offices
Office traffic is often heavily influenced by arrival, lunch and departure periods. Large numbers of people may travel from a common entrance to different floors within a relatively short time.
Hotels
Hotel lifts deal with guests, luggage and operational movements throughout the day. Check-in, breakfast and check-out periods can alter demand, while staff may need separate service routes depending on the building.
Residential Buildings
Residential traffic is generally more dispersed, although busy periods still occur. Residents may also travel with pushchairs, bicycles, shopping, luggage or mobility equipment, which affects how much usable space is available inside the lift.
Healthcare Buildings
Hospital and healthcare lifts can need to accommodate wheelchairs, beds, trolleys, equipment and staff movements. Journey priority and the physical size of what needs to be transported can be just as important as passenger numbers.
Education Buildings
School, college and university lifts can experience concentrated movement between lessons, lectures or teaching periods. A lift may also be important for accessible circulation even when the majority of students normally use stairs.
Understanding the building’s actual use is therefore essential before applying assumptions taken from another type of development.
Waiting Time Matters
From the passenger’s point of view, lift performance is often experienced as waiting.
A journey lasting another ten seconds once someone is inside the car may barely be noticed. Standing at the landing while several full cars pass can be a very different experience.
Traffic analysis can help assess how the proposed lift arrangement is likely to perform when demand increases.
This is particularly relevant in larger commercial developments where poor lift provision can create queues in reception areas and affect circulation through the building.
It also explains why adding capacity to an individual lift isn’t always the answer. Sometimes the issue is how frequently a car becomes available rather than how many people can fit into it.
What Happens When One Lift Is Out of Service?
This question is easy to overlook during the design stage.
A building with three lifts does not necessarily have three lifts available every minute of its working life.
Equipment needs servicing. Inspections are required. Modernisation work may eventually be necessary. Unexpected faults can also occur.
Traffic planning should therefore consider how the building operates when normal lift capacity is temporarily reduced.
The effect depends heavily on the building.
In some premises, longer waiting times may be inconvenient but manageable. In others, losing a lift can affect accessible routes or the movement of essential equipment.
Where uninterrupted vertical movement is particularly important, resilience should form part of the original lift strategy rather than being considered only after the building is occupied.
When Is Formal Lift Traffic Analysis Needed?
Not every project requires a complex traffic study.
A small, low-rise building with modest and predictable lift use may be relatively straightforward to assess.
Traffic analysis becomes more valuable as the building, population or movement pattern becomes more complicated.
It should be considered particularly carefully where there are:
- Large numbers of occupants
- Several floors
- Concentrated arrival or departure periods
- Multiple lifts
- Mixed building uses
- High reliance on vertical circulation
- Existing problems with queues or waiting times
- Major refurbishment or redevelopment work
It can also be useful when an existing building is changing use.
An office being converted into another type of accommodation may retain the same floors and lift shaft, but the demands placed on the lift can change considerably.
The existing lift arrangement should not automatically be assumed to suit the new use.
Traffic Analysis Should Happen Before the Lift Is Specified
One common mistake is to select a lift and then ask whether it will cope with the building.
The sequence should be the other way around.
First establish how the building will be used, who needs to move through it and when the busiest periods are likely to occur. That information can then inform the number of lifts, capacity, speed, door arrangement and control strategy.
It can also affect the physical design of the building.
If analysis shows that two passenger lifts are required rather than one, finding that out after the lift shaft has been constructed creates an obvious problem.
The same applies to refurbishment. Existing shafts and structural constraints may limit the available options, making it even more important to understand which aspects of lift performance actually need improving.
Lift traffic analysis is therefore not simply a calculation about how many people fit into a car. It is a way of understanding how vertical movement fits into the operation of the building as a whole.
Getting that right at the design stage is considerably easier than trying to solve queues, waiting times and insufficient lift capacity once the building is occupied.
Frequently Asked Questions About Lift Traffic Analysis
What information is needed to carry out lift traffic analysis?
The information required depends on the project, but it can include the building type, number of floors, expected occupancy, location of entrances, proposed lift capacities and how people are expected to move through the building. More complex developments may require additional information about peak periods and different user groups.
Can lift traffic analysis be carried out for an existing building?
Yes. Existing buildings can be assessed using information about current occupancy, lift usage, waiting times and any known problems with the existing arrangement. This can be particularly useful before refurbishment, modernisation or a change of building use.
Should lift traffic analysis be reviewed if a building changes use?
Yes. A change in use can alter both the number of occupants and the way they move through the building. An existing lift arrangement that worked well for one use may not provide the same level of service after the building has been converted or significantly reorganised.
Does lift traffic analysis consider disabled users?
Accessibility needs should form part of the wider lift specification. Wheelchairs and mobility equipment can affect usable car space, while some occupants may depend on the lift as their primary means of moving between floors. These requirements should be considered alongside general passenger demand.
Can traffic analysis help decide whether destination control is needed?
In larger or more heavily used buildings, traffic analysis can help identify whether different control strategies may improve passenger movement. Destination control is one possible option, but its suitability depends on the number of lifts, building layout, passenger demand and operating requirements.
How often should lift traffic requirements be reviewed?
They do not normally need constant reassessment, but a review can be worthwhile when occupancy changes significantly, the building is refurbished, its use changes or persistent waiting-time problems begin to appear. Major lift modernisation can also provide an opportunity to reassess how the building is now being used.