Most building defects trace back to a decision made too early, by someone who didn't yet have the data to make it. Lift provision is one of the clearest examples. Core size, lift count, and shaft position are usually locked in during concept design, months before anyone runs a proper lift traffic analysis, and long before the building's actual population, floor plate mix, or peak-hour behaviour is fully understood.
By the time a traffic study does happen, it's often a compliance exercise rather than a design input. The core is fixed, the architect has moved on to the next stage, and the numbers that come back — average waiting time, handling capacity, interval — land as a report to file, not a decision to make. That ordering problem is worth examining, because it's costing developers money and occupants patience on buildings that are otherwise well designed.
What Lift Traffic Analysis Actually Tells You
A traffic study models how people move vertically through a building across a working day, not just at the theoretical worst-case peak. The output isn't a single number; it's a set of interlocking metrics: interval (how often a lift arrives at the main entrance), handling capacity (the percentage of the building population that can be moved in a five-minute period), and average waiting time. Together they describe whether a lift installation will feel adequate to the people using it, or whether it will produce queues at 8:50am that no amount of clever lobby design can hide.
These figures are set out in detail in CIBSE Guide D: Transportation Systems in Buildings, which remains the standard UK reference for how lift performance should be assessed and specified. What the guide can't do is tell a project team when in the programme that assessment should happen — and that's the part most projects get backwards.
The Cost of Leaving It Until the Core Is Fixed
Once a core is poured, the number of shafts, their width, and their position relative to the lobby are essentially fixed. If a traffic study run afterwards shows the building is under-lifted — a common outcome on mixed-use schemes where floor plates change use partway through design — the options left are all expensive: destination control retrofits, lobby remodelling, or simply living with waiting times that undermine the building's grade.
Running the analysis earlier, even at concept stage with provisional population and floor-area figures, doesn't eliminate uncertainty, but it turns lift design into an input the architectural team can actually respond to. A core that's one shaft too narrow is a sketch-stage fix. A core that's one shaft too narrow after RIBA Stage 4 is a claim.
This is rarely a case of the original consultant getting the sums wrong. It's usually that the brief itself moved — a floor of offices became co-working space with three times the occupant density, a podium originally planned as back-of-house became retail, or a hotel scheme added a conferencing floor after the core was already set. Static traffic calculations, run once against an early brief, have no mechanism for flagging that the assumptions underneath them have quietly stopped being true.
Simulation Over Static Calculation
Traditional traffic calculation assumes a single, simplified up-peak pattern and applies formulae to it. It's fast, and it's fine for a first pass, but it struggles with the buildings that are hardest to get right: multi-tenanted towers with staggered start times, buildings with a retail podium and office floors above, or schemes with destination-control dispatch that a static formula was never designed to model.
Purpose-built traffic analysis from AdSimulo addresses this by simulating the building over a full day rather than a single theoretical peak — lunchtime interfloor movement, lobby congestion, mixed passenger groups, and multiple dispatch strategies can all be tested against each other before a single shaft is dug. The design team gets to see the trade-off between, say, four larger lifts and six smaller ones, rather than taking it on faith from a spreadsheet.
What to Ask For, and When
Project teams don't need to become vertical transportation specialists to get this right. They need to ask for a traffic study at concept design, not at technical design, and they need to ask for it to be revisited whenever the brief changes population, use class, or floor count — all of which happen more often than programmes admit.
The questions worth putting to a lift consultant early are simple: what handling capacity and interval is this design achieving against the intended population, what happens to those figures under a mixed-use or staggered-occupancy scenario, and has that been tested through simulation rather than a single static calculation. Answers to those three questions, obtained before the core is fixed, prevent most of the retrofit problems that show up two years after handover.
It's also worth building a re-check into the programme itself, rather than treating the first traffic study as the last. A single review gate at RIBA Stage 2, and a second at Stage 4 once the brief has settled, costs a fraction of what a lobby remodel or a destination-control retrofit costs after occupation — and it gives the project team a defensible answer if a client or funder later asks how lift provision was validated.
The Takeaway
Lift performance is one of the few pieces of a building's servicing that occupants notice every single day, and one of the few that's genuinely difficult to fix after the fact. Treating traffic analysis as an early design input rather than a late-stage compliance check costs little and closes off some of the most expensive mistakes a scheme can make.