Melissa's Hot Takes

What is the Empty Bus Myth?

You’ve heard it before. “Why are we paying to run empty buses? Everytime I see a bus, there is nobody on it!”

Excusing the fact that there is absolutely no way that this can be true, we may be tempted to agree with the underlying premise. Why are we funding a service that is clearly underutilised?

Fortunately, this line of thinking is illogical. Firstly, this is not how we talk about other forms of transportation. When was the last time that you heard someone say: “Why are we paying for a road that nobody drives on?” Secondly, it ignores that there may be a valid reason that the bus is empty – for instance, that it is at the start or end of its route. Thirdly, it may not even be the case that the bus is empty! The windows of a bus are relatively higher than the windows of a typical motor vehicle; if a passenger is even slouching a little, it is entirely plausible that someone outside the bus may not even be able to see them.

The point of this article, however, is to mathematically prove the folly of this statement. My hypothesis (Footnote 1): A nearly empty bus is still a more efficient mode of transport than a car.

Why Am I Writing This? I am writing this so you can send this to the next person who says that we should not be funding so-called ‘empty buses’.

Why Should You Listen to What I Have to Say? I have recently completed a Master of Environmental Planning (read about my experience here!), and I completed a Bachelor of Science in Physics and Mathematics several years ago. I have the ‘know-how’ and ‘can-do’ when it comes to calculating the numbers of our transit system.

The Math.

According to Stuff, the Ford Ranger is the most popular new car in Aotearoa New Zealand. The Ford Ranger XL has an overall length of 5.35 m (210.9 in).

Woah, look at how cool it is! Photo from Ford.com.

Waka Kotahi provides the specifications for the standard bus in Aotearoa. The length of a large, single decker bus, such as those common in my hometown of Kirikiriroa Hamilton, is 13.5 m.

The most valuable infrastructure in our cities. Change my mind. Front bus image from Waka Kotahi; side bus diagram from Our Auckland.

We may automatically assume, therefore, that the bus is two and a half times longer than the motor vehicle. However, we must also take into account that in actual traffic, motor vehicles are not aligned bumper-to-bumper; in fact, there is a buffer space between vehicles. A rule of thumb is that you should stop where you can see the tires of the vehicle ahead. We will generously call this 2 m. This means that the bus is approximately two times longer than the motor vehicle.

A comparison of the two vehicles, including the space between the cars that arises in normal traffic. Ford image from Ford.com; bus image from Our Auckland.

The driver is the sole occupant of the vehicle in two-thirds (68%) of trip legs according to data collected by Waka Kotahi. Again, let us make a generous assumption that one vehicle has one occupant and the other vehicle has two occupants.

This means that for the motor vehicle, we have three total passengers over a length of 12.5 m.

Now, let us consider the bus. That means that the bus only needs to have three passengers (we are not going to include the driver) to be an as efficient use of space as the motor vehicle. If the bus is carrying at least four passengers? It is more space efficient than the car.

Is that really so empty? Diagram by Melissa Smith.

A single decker bus can carry between fifty-five and seventy-five passengers (both sitting and standing) according to specifications from Waka Kotahi. To be generous to the motor vehicle, we will take fifty-five passengers as the maximum passenger capacity. This tells us that a bus at 5% capacity is as space efficient as a car at 25% capacity (Footnote 2).

Is that not incredible?

Footnote 1. I know this is not the proper use of the term, but roll with me here.

Footnote 2. If every single person riding that bus were driving to their destination as well, that would not only gobble up 100 parking spaces within the city, it would also take up a whopping 735 m of road space, or over half a kilometre. That would add a lot of time to your commute.