Elevator traffic analysis explained: why your building needs one

If you have ever waited too long for an elevator in a busy building, you have felt what happens when traffic analysis is done badly or not at all. Traffic analysis is how engineers work out how many elevators a building needs, how fast they should be, how large the cars should be and how the system should be arranged to give good service.

It is often skipped or treated as a formality. Here is why it deserves more attention, and how it works.

What is elevator traffic analysis?

It is a simulation. Using specialist software, engineers model how people move through a building and test how different elevator arrangements cope.

The analysis looks at:

• The building's population. How many people are on each floor, and how crowded does it get at peak?
• Traffic patterns. When people arrive in the morning, leave in the evening, move between floors, and go out and come back at lunch.
• The elevators. How many, how fast, how quickly they accelerate, how many people they carry, and the type and timing of the doors.
• The arrangement. Zones, groups, express service, sky lobbies and the control method.
• The targets. The longest acceptable wait, how many people the system must carry, and the grade of service expected.

The result is a detailed forecast: the average wait, the longest wait, the handling capacity (the share of the building's population the elevators can move in a five-minute peak) and how long the queues in the lobby will be.

Why does it matter?

For a new building

During design, traffic analysis answers the basic question: how many elevators do we need, and what should they be?

Getting it wrong is costly either way:

• Too few elevators means long waits, unhappy tenants and lower rents.
• Too many elevators means wasted money, lost lettable floor space and higher maintenance costs for life.

Each elevator shaft in a typical tall building takes about 3 to 4 square metres on every floor. In a 40-storey building, one unnecessary elevator costs 120 to 160 square metres of lettable space. Over the building's life that is a large sum.

For an existing building

In a building already in use, traffic analysis helps find the cause of poor performance and test ways to improve it. Typical cases:

• Tenants complain about waiting. Are there too few elevators, or is it a control or settings problem?
• A floor changes use. Turning an office floor into a call centre changes how many people are there and how they move.
• A modernization is planned. How much improvement will a new controller bring, and will it be enough?

How the analysis works

Step 1: describe the building

The engineer enters the building's physical details:

• The number of floors and the height between them
• The population of each floor, or the density per square metre
• The type of use: office, residential, hotel, hospital and so on

Step 2: describe the elevators

The proposed or existing system is modelled:

• The number of elevators and how they are grouped
• Speed, acceleration and smoothness of ride
• Car capacity and dimensions
• Door type, width and opening and closing times
• Controller type and control method

Step 3: set the scenarios

Several scenarios are run to test the system under different conditions:

• The morning arrival peak, which is the hardest test for offices
• The evening departure peak
• Two-way traffic at lunchtime
• Movement between floors
• Emergency evacuation, where regulations require it

Step 4: run the simulations

The software simulates thousands of journeys and follows each person from pressing the call button to arriving at their floor. Modern tools model individuals: when they arrive, where they are going and how long they take to step in and out.

Step 5: judge the results

The results are compared with industry benchmarks:

These are general guidelines. Exact targets vary by region, market and class of building.

Common mistakes we see

1. Rules of thumb in place of simulation

Simple formulas such as "one elevator for every so many floors" were acceptable decades ago. They are not enough for modern buildings, because they ignore traffic patterns, control methods and the way several elevators in a group affect each other. Simulation is the industry standard.

2. Looking only at the morning peak

The morning arrival is usually the hardest test for an office building, but it is not the only one. Lunchtime, when people travel up, down and between floors all at once, can be just as demanding. A system tuned only for the morning may perform badly at lunch.

3. Unrealistic population figures

Underestimating how many people will use the building is the most common error. If the analysis assumes 10 square metres per person and the real figure is 7, the elevators will underperform from the first day.

4. Ignoring future growth

Buildings change. Floors change use, tenants fit more people in, and new features such as roof terraces and gyms create extra journeys. A good analysis allows a margin for growth, usually 15 to 20 per cent above the expected population.

When to commission one

• New buildings: at concept or first design stage, then updated as the design develops.
• Modernization: before deciding the scope, to establish current performance and set targets.
• Change of use: whenever a significant change in how floors are occupied is planned.
• Disputes: when the owner and the elevator contractor disagree about performance.

What you receive

A traffic analysis report from Doug & Danny includes:

1. A summary of the main findings and recommendations
2. Detailed results for every scenario simulated
3. A comparison showing how several arrangements perform
4. A growth test showing how the system copes as the population rises
5. A clear recommendation on the best arrangement
6. Notes for the architect on shaft dimensions, pit depths and headroom

The report gives you the evidence to make design decisions with confidence. It also sets the standard the installed elevators can later be measured against.

Get your traffic analysis

Whether you are designing a new building or solving problems in an existing one, a professional traffic analysis gives you the facts you need to decide well.

Ask about a traffic analysis

Doug & Danny uses leading simulation software to produce accurate, practical traffic analysis for buildings of every type and size in Saudi Arabia, the GCC and the United Kingdom.