When people want to imply that public transit is irrelevant or failing or wasteful, they always point to relatively empty buses or trains. To the layman it certainly seems as though buses with few passengers aren’t achieving much.
This common line is based on two false assumptions. It assumes that empty seats indicates waste, which they usually don’t, and it falsely assumes that ridership is transit’s only measure of success, which it isn’t.
The Math of Efficiency: Run the Biggest Bus You Will Ever Need
In fact, when a transit agency runs a relatively empty bus, they’re doing what they’re told to do, and they’re doing it efficiently.
Transit operating cost is mostly labor. The cost of a bus is in the driver, not the size of the vehicle. So it doesn’t cost much for the vehicle to be bigger than needed.
But it costs a lot for the bus to be too small. Then you have crowding, or you leave passengers behind.
Demand for transit goes up and down during the day, and on different parts of the route. It also goes up and down for unpredictable reasons. A school decides to have a field trip, and a normally empty bus is suddenly packed. Nice or bad weather can change ridership patterns suddenly.
Buses and trains cannot dynamically shrink or expand to match these changing demands, and since the operating cost lies mostly in the driver, there wouldn’t be much to gain by doing that. For example, you might propose that after the morning rush hour the big buses should be replaced by smaller ones. But the cost of paying a driver to take a bus back to the base and take out a different one far exceeds any cost in running a larger bus than you need for a few hours.
So transit agencies are smart to run the biggest bus they will ever need, even though that means the bus will be empty at some hours, or on some parts of the route, or even on some days when demand is lower. They may even run a bigger bus than a route ever needs, because there are also massive inefficiencies in having too many different kinds of buses. Smart agencies have thought this through and what they are doing, in my experience, mostly makes sense.
Ridership Is Not Transit’s Only Measure of Success
If ridership were the only goal of transit, it would look very different. For example, it wouldn’t serve many parts of the city, because high ridership is just geometrically impossible in those places, for reasons we explain here. For example, it would delete a service that almost nobody is using, and it wouldn’t waste five seconds on people’s complaints that they really need or deserve that service.
The people who govern transit agencies — who are either elected officials or their appointees — almost never tell their staffs to run the agency this way. They want ridership, but they also want a lot of other things that often justify running low-ridership service.
The 2020 Covid-19 epidemic proved this point. Instead of shutting down and laying off most staff, as a profit-making business would logically do, most big city agencies did their best to run service, not just to keep their staff employed but also to enable those “essential service” workers to get around, so that the city could keep functioning. To do this, and to encourage social distance, they ran intentionally “empty” buses and discouraged people from riding them. In this, transit revealed itself to be the opposite of a business. It’s a utility, an essential element of the functioning of a city.