When we think about motorized transportation, we usually think about moving horizontally. Sometimes flipping your perspective and looking at a slightly different problem yields new insights. So let’s look at vertical transportation (that is, elevators) and see what we can learn about ground transportation.
1 Measuring people throughput is more important than vehicle throughput
How many people does an elevator car carry in an hour? You can’t just look at how many times the car travels through the shaft but also how many passengers are in the car each ride. If etiquette said we don’t share elevators but each take our own, it would take forever to serve a major tower.
You can say the same for car lanes. Vehicle throughput gets a lot more press but passengers per vehicle is just as important. When a car lane reaches maximum vehicle throughput, the only way to move more people is to get more people in the same vehicle by carpooling or taking buses or trains.
2 Adding more elevators gets higher throughput but only up to a point
Small buildings often only have one elevator. As buildings get bigger, you need more of them to move all the people. But this process can’t be repeated indefinitely. Each new elevator shaft moves more people but also takes a bite out of the floor plate used for offices or homes. A tower needs to go ever higher to fit the same number of people. By the time a building reaches 50, 100, or 150 floors, this becomes a very important consideration. You need to make each elevator shaft more efficient because new shafts take away from the intended use of the building.
Lay that logic on its side and you get something interesting! The more lanes that you add to streets, the less room there is for destinations. The wider the streets get, the further apart homes and workplaces need to sprawl. Eventually, the strategy stops working altogether and the only option is to make streets more efficient at moving people per lane, not adding more lanes.
3 Reducing dwell time matters
One of the more interesting elevator innovations is destination dispatch, a system where users enter their floor prior to entering the elevator. One way this helps is that the elevator can get going more quickly after each stop, as it doesn’t need to wait for the new entrants to press the button for their floor. Combining this benefit with the benefit from grouping passengers more efficiently, some elevator companies estimate they can get more than 30% better throughput from the same number of elevators.
Transit users don’t usually need to designate their destination at the time of entry, of course. But they do sometimes stop and interact with drivers for a different reason: paying fare. Transit systems that allow riders to pay fare prior to entry can reduce dwell times for buses just like destination dispatch reduces dwell time for elevators. (This is also true for for-hire vehicles.)
4 Circulation can help throughput
As buildings get taller, a single elevator shaft can get less useful: as there are more stories, there are fewer cars per floor and cars may have to travel further to pick a passenger up. You could potentially get multiple cars in the same shaft but you have to deal with elevator traffic! If, though, you use an elevator that can go sideways, then you can sidestep another car in the shaft, go to another shaft, and keep moving.
In horizontal world, this can already be done! Unlike elevator shafts, it’s pretty easy for a vehicle to move from one street to another and sidestep traffic jams — if (and it’s a big if), there’s good “sideways connectivity” with many cross-streets allowing you to turn onto a different street.
5 Security matters
Elevators can be scary places. You’re trapped in an enclosed space with other people with nobody else watching. Since public elevators switched from a transportation technique with an operator to a self-operated transportation technique, there has been a continuous increase in security techniques to help people keep both being and feeling safe inside elevators, from emergency call buttons to surveillance. I don’t know what the proper security techniques are for public transportation, but evidence from elevators suggests that it’s a problem worth solving.