Return to the office means an elevator bottleneck, unbearable lines
Limited occupancy in elevators means long lines and wait times
Now that Pfizer and Moderna are beginning to roll out coronavirus vaccines, return to office planning is expected to ramp up. This is good news for office property managers, who have endured low occupancy levels since the start of the COVID-19 pandemic.
As tenant re-entry begins, the health safety measures taken by property managers will soon be put to the test. For example, most buildings are limiting elevator occupancy to 4 or fewer passengers at a time to ensure social distancing, as recommended by the CDC. While this measure has little impact on elevator service when building occupancy is below 10%, elevator traffic experts say these limited occupancy rules can (and likely will) cause a bottleneck to form at the elevators—especially at lunchtime and during the evening rush hour.
The reason for this is simple—every elevator system has a saturation point that is crossed when more passengers need the elevator than can be moved through the system at one time. If you’ve ever called the elevator, saw it was full, and had to wait for the next one, then you’ve probably experienced elevator saturation. And as you likely remember, it was a frustrating (not to mention wasteful) experience for everyone involved.
By limiting elevator occupancy to a fraction of what it used to be, the elevator system in a building could experience saturation events when only 30 or 40% of the total building population returns (unless appropriate measures are taken to reduce elevator demand). Some studies suggest that elevator wait times could be an hour or more at peak times. With passengers being accustomed to waiting 30 seconds or less for the elevator, buildings will need to decide on how to prevent the bottleneck if they want to keep their tenants happy.
Of course, occupancy limits could be removed, but there are liability concerns in doing so that will prevent crowding elevators like people used to do. This means that elevators will continue to have limited occupancy for some time.
What does a bottleneck look like?
Imagine three different scenarios; people going into their office building in the morning at 8am, people going out to lunch at 11:30am, and people leaving work at the end of the day at 4pm. In the morning, you walk into your building and see a line formed in the lobby leading to the elevator banks. You wait and wait until it is your turn to get into an elevator with 3 other people. You are headed to the 34th floor. Once inside, the ride is relatively quick as the elevator only makes stops for the 4 passengers going up to their offices.
At lunchtime, you and a group of coworkers are excited to get lunch together. You made reservations for a restaurant at 11:30am and head for the elevators at 11:20am. One of you presses the down button and you all wait, chatting and laughing (as we’re all starved for social interaction at this point!). 30 seconds pass, then a minute, and then another minute. You all begin to get impatient with each passing minute. You press the button again thinking maybe it hasn’t registered correctly. You look at your phone and it’s 11:28am. Finally, the elevator door opens, only to be filled with passengers and already at capacity. You now have a choice to make: overcrowd the elevator (and violate CDC guidelines), or wait for the next elevator and leave everyone frustrated and impatient.
At the end of the day, you go to the elevator at 4pm with a coworker. You call it, and after waiting a minute, the elevator door opens with no one inside it. You were on the verge of panic, but relief washes over you when you realize you actually have an elevator to yourselves! You get on and press the lobby floor button. The elevator doors close, you feel the elevator move, and you see the floor counter change from 34 to 33. The elevator slows down, the doors open, and three other people get on, overcrowding the elevator. The doors close, you feel the elevator move once more, but again, the elevator immediately decelerates the moment it gets moving to stop at the 32nd floor. Two more people ask to get on, no one says a word, and the elevator ride starts to get uncomfortable.
The elevator continues to do this all the way down to the lobby, making stop after stop. You go from relieved to panicked, as the elevator gets completely overcrowded and all of the passengers get visibly irate. With each additional stop, you feel the level of anxiety and frustration of each passenger bubble up. As the doors continue to open, you see lines form on every floor and see the people waiting also get understandably impatient as they realize the elevator is already full, and they will need to wait even longer for the next one.
Why does an elevator bottleneck form?
The fact that passengers usually wait less than a minute for the elevator is a result of careful planning, expert design, and extensive simulations — long before the building itself is even constructed. The process of designing and analyzing elevators is complex, often involving some combination of manual calculation, simulation, and observation of existing buildings. The goal of these analyses is to design a vertical transportation system that can efficiently move passengers through a building during peak periods of the day, without significant delays.
It is a common misconception that waiting time increases linearly with passenger demand. If the average waiting time were 20 seconds when moving 8% of a building’s population every 5 minutes, then it would be logical to assume that the waiting time would increase to 40 seconds when moving 16% of the population in 5 minutes. However, experience and simulation show this to be incorrect.
The relationship between passenger demand and average waiting time is not linear. A major contributing cause of this non-linearity is a significantly increased number of intermediate stops and passenger queuing. In other words, an overloaded elevator will make many more stops per round trip, many of which are unnecessary after the elevator is fully occupied.
As mentioned earlier, when passenger demand exceeds an upper threshold, the elevator system reaches saturation — the point at which a passenger may wait many minutes, or even hours, for an elevator. As shown by the dotted line in the graph above, this saturation point drastically shifts when limiting elevator occupancy in compliance with CDC health guidelines because elevators carry fewer passengers and make many unnecessary intermediate stops to pick up additional passengers — even when the elevator is already at capacity. As buildings seek to limit liability and accommodate health conscious tenants both during and after the COVID-19 pandemic by limiting elevator occupancy, the saturation point for most buildings remains unknown.
How can I address the elevator bottleneck on a limited budget?
Emerging occupancy sensing technologies will play a vital role in re-densifying buildings both during and after the COVID-19 pandemic. By monitoring the occupancy levels in each elevator in a building, only elevators that are able to pick up additional passengers will respond to hall calls, while full elevators will prioritize delivering the in-car passengers to their destination. This occupancy sensing technology is a fraction of the price of other available solutions, such as destination dispatch and multi-car systems — both of which are major modernization projects that don’t fully solve the elevator bottleneck while taking months to years of planning and execution.
If a building on a limited budget wants to prepare for tenant re-entry in the coming months, such major projects fall well outside of the realm of possibility. A more practical solution involves retrofitting elevators with state-of-the-art occupancy sensors—which can be installed in a matter of hours—to improve throughput, simplify compliance with health guidelines, and constantly gather rich, anonymized passenger data to help coordinate tenant re-entry.
