Any hotel above a certain size runs two elevator systems that never mix. The separation is a capacity decision, and the building is designed around it from the start.
Service traffic is bulkier than guest traffic
A housekeeping cart, a linen hamper, a room service trolley and a maintenance ladder each occupy most of a cab. None of them can share space efficiently with people.
The volume is also relentless. Every occupied room generates linen out, linen in, amenities, trash and often a food delivery, all of which move vertically.
Running that through the guest elevators would consume the cabs during exactly the hours guests need them, which is the morning and the early evening.
The two systems have different shapes
Service cabs are typically taller, deeper and fitted with protective wall padding and durable floors, because they are loaded with hard-edged equipment all day.
They open onto service corridors, back-of-house landings and loading areas rather than onto guest lobbies, so a cart never crosses a public space when it can be avoided.
Guest cabs are optimized for speed and appearance instead, with shallower floors and finishes that would not survive a linen cart.
Access control keeps the split intact
Service elevators are usually restricted by staff credential, which prevents them from becoming an informal shortcut that reintroduces the congestion they were built to avoid.
Guest cabs on floor-restricted systems work the other way, releasing only the floors a card is entitled to reach.
Both restrictions serve the same purpose, which is keeping each system carrying the traffic it was sized for.
The split explains where amenities are placed
Ice machines, vending and linen closets sit near the service core, because that is where restocking arrives without crossing a guest corridor.
Rooms immediately beside that core hear the traffic, which is why experienced travelers ask for something away from the elevator bank and the service door.
Suites and premium categories are usually positioned at corridor ends, farthest from both cores, and that distance is part of what the category is selling.
What happens when a cab goes down
Taking one service elevator out of commission in a tall hotel forces carts and deliveries onto the remaining cab or, temporarily, onto guest elevators.
The visible symptom is a sudden wait in the lobby and carts appearing in guest corridors at odd hours, well before any notice is posted.
Properties respond by shifting delivery windows earlier and staging supplies on floors overnight, which is why an outage often produces stacked linen at the end of a hall.