What’s Wrong with an Empty Bus?

Why is this bus in Paris empty? It’s parked at the end of the line.

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.




8 Responses to What’s Wrong with an Empty Bus?

  1. Anonymous April 7, 2020 at 11:13 am #

    “Buses and trains cannot dynamically shrink or expand to match these changing demands”
    Multiple unit trains can be coupled together to make longer trains, but even then it doesn’t seem to be very common to actually do it, basically unheard of on metros (even the ones which could do it) and getting rare on electrified suburban rail.

    The cost issue raised here also only applies to high wage countries, in low wage countries vehicle size can matter much more (and so you get minibuses which wait until every seat is full before departing).

    • Fbfree April 7, 2020 at 12:29 pm #

      The Chicago ‘L’ has been known to use 8-car trains at rush hour and decouple them to 4-car trains off-peak on some lines as vehicle maintenance is a significant fraction of the operating cost for those trains.
      This is only on lines that already have a lot of excess capacity, in order to maintain frequency.

      • Mtnsguy April 9, 2020 at 1:03 pm #

        Metra runs the same trains all of the time. They do not change the size of trains, either during the day or during the week. In fact, they will remove locomotives for servicing, but not rearrange the trains except for needing to take the cars out of service for repair. On weekends and off-peak, they will only open a certain fraction of the cars in a train to customers. On weekends, for example, it is not unusual to see a 10-car train on the UPNW line (where I live) with only four cars open for customers.

    • asdf2 April 8, 2020 at 10:38 pm #

      Coupling and decoupling trains takes time, which means man-hours, which means $$. It would not at all surprise me if it’s cheaper to just run the rush-hour-sized train all day than to pay people to uncouple half the cars at the end of morning rush hour and attach them again at the start of evening rush hour.

      Also, routes that share tracks with freight trains have minimum weight regulations imposed by the government. If they uncoupled half the cars, the trains might not even be legal to operate.

  2. Eric Brightwell April 8, 2020 at 9:21 am #

    I’ve heard these complaints — inevitably from people who would never use mass transit under any circumstances — to justify their complete reliance on an automobile. I have two responses for them:
    1. I’ve never been on a bus or train and thought to myself “If only there were more people on this thing!”
    2. When is the last time your car was filled to capacity?

    • Murray April 8, 2020 at 3:34 pm #

      Good point about the cars. Given the standard usage, most people should be going around on motorbikes.

    • Mtnsguy April 9, 2020 at 1:09 pm #

      I don’t know anyone who has ever said, “I wish there were more traffic on this road, it’s too empty! Or, driving along a major thoroughfare at 11 pm, “There are too many lanes here. This proves we really only need one lane in each direction!”

  3. jean-francois cantin April 8, 2020 at 9:22 pm #

    Most people use their car about 5% of the time, yet it’s not seen as a waste. They will buy a SUV because they can fit more stuff in it yet most of the time the trunk is empty or filled with junk. It’s not seen as a waste. A empty bus is the same, it’s not a waste, it’s a available capacity for somebody to make a trip.

    A bus would not be full most of the time even in peak hour because you have a fix geometry and it will fill up on is way to the main destination. it’s not full from the beginning of the line.

    Also having different size of vehicule it really not optimal for the maintenance crew. You need to train the maintenance crew on each model, maintain an inventory of replacement part for each model, etc.

    Having bigger bus also allow the agency to offer the same capacity on a route with less bus and less driver. Pretty important knowing the staff shortage most agencies faces. They do need to find the balance not to impact to much the frequency because then it loses its attraction.