When is a Bus Worth It?

Our cars are getting bigger and have gotten bigger in a bad way. Remember when the Hummer H2 was considered a grossly large vehicle? In 2002 when it was released, the size of the H2 was its own cultural flashpoint, as though Hummer had gone out of the way to mock the detractors of its original vehicle by making a larger and more audacious vehicle. I looked back at some coverage and found a pretty fascinating article about the appearance of the first H2s in the Bay area. In this article, the H2 is called an “ultimate arrogant driving machine,” a “four-wheel leviathan,” and an “unrepentant road hog.”

Harsh, and I can’t disagree, but the H2 doesn’t feel so big these days. I remember seeing a Hummer for the first time and being astounded. Nowadays? I only register seeing one because it’s a somewhat uncommon car. 

Out of curiosity, I went to Carsized.com, a website that allows you to visually compare different vehicles and compared the H2 with a vehicle I see every day on the urban streets of Denver, a modern Chevy Suburban. As it turns out, the Suburban is about as tall as the H2, and quite a bit longer, yet I don’t see a whole lot of reporting on how this vehicle is the ultimate arrogant driving machine. 

The reason is contextual size. 22 years ago, the H2 towered above other cars, a sore thumb in a sea of sedans and smaller SUVs and trucks. Today, the road is crowded not simply because there are 50 million more cars registered than in 2002, but because those cars have gotten bigger and bigger. From 2013 to 2023, the average car in the US got one foot wider and one foot, ten inches longer. That’s a lot of space. We’ve boiled the frog, and as a result of these monstrous vehicles we are paying the price with road deaths on an upward trajectory since 2009.

But this isn’t an essay on road safety and the causes of large vehicles in the US, much ink has already been spilled on this front. It’s obvious that a vehicle like the Suburban is a significantly less efficient way to travel than something like a Smart Car (discontinued because of slow sales). Beyond that, it is much less societally “worth it” to drive something like a Suburban when factoring in things like land use, emissions, and cost to operate.

My revulsion to huge cars, trucks, and SUVs calls into hypocrisy something I have deep affection for: the bus. If the Suburban is a leviathan of the roadway, then a bus is a titan. Here in Denver, our RTD Buses are 8.5 feet wide, 40 feet long, and 9 ¾ feet tall – that is huge! This got me thinking, how does a bus fare (pun intended) societally when measured against the baseline of a car? That is, when would it be the socially-optimal decision to have folks driving instead of riding the bus? If a bus provided service to one rider a day, certainly we would all be better off if that person simply drove themselves or we could provide a rideshare. I decided to look at this worthiness on three fronts – how much space a vehicle takes up, emissions per person, and costs to society.

Space

As I’ve alluded to, the Suburban, H2, and other road giants are also not particularly efficient ways of moving people around. Sure, if all 9 seats in the Suburban are full, that’s actually not a terrible way of getting people from place to place, but the Department of Energy reports that the average occupancy of an SUV is 1.7 people per trip, just .3 more than a sedan. And these SUVs are huge, here is a little comparison I made of a Suburban and an RTD bus:

Here is what that looks like visually:

Suburbans are about half the length of a bus! I knew these vehicles were huge, but this still shocked me. Using one of these to shuttle yourself from place to place is a pretty silly way to get around, and is evidence that we aren’t always rational with our mode-choice. A teeny vehicle like a Smart Car, however, might get you a bit more efficiency from a road-space perspective. Both to give cars their best shot of success here, and to be able to compare different sizes of personal vehicles, I’m going to include both the Suburban and the Smart Car in my comparisons. I should note, though, you’re exceedingly unlikely to spot something Smart-Car-sized on the roads, whereas you’ll count dozens of cars like the Suburban on a typical American commute (over half of cars in Colorado are SUVs, only about 28% are sedans). For the record, here is a Smart Car and a Suburban, wowie:

So, for reference, here are how the sizes of these vehicles compare to one another:

When we’re thinking about roadway space efficiency, though, we don’t actually care all that much about height. A taller vehicle doesn’t translate into more street parking issues, traffic congestion, or merging problems. So, as I compare the space of these vehicles, that isn’t all that important. Width is a bit trickier – does it really matter that a bus is wider than the other vehicles? Other than maybe, maybe the argument that roads are designed wider to carry buses (which I have no evidence for), vehicle width doesn’t seem to matter much from a space perspective. Cars and SUVs are probably narrower than 7’ because any wider and drivers would feel uncomfortably close to the lane markers, a worry that a professional bus driver doesn’t share. 

What this means is that vehicle space efficiency is a primarily measure of vehicle length per person. Fantastic, we can calculate that easy peasy. Using the average passenger statistics referenced above, we find that a Smart Car driving down the road uses 6.31’ of length per passenger, while a Suburban uses 11.07’ per passenger (8.83’/1.4 passengers and 18.81’/1.7 passengers, respectively). From there, take the 40 feet and divide it by feet per passenger, and you have your answer! Purely from a space perspective, people should be switching from Smart Cars to buses when 6.34 or more can climb aboard, and should get out of their Suburbans when 3.62 can board.

This doesn’t take into account parking. Parking – street parking in particular, but all parking – is a horrible use of land, and private automobiles account for nearly all parking demand. Buses don’t park on the street or in surface lots, and so they more or less have an infinite advantage here. I don’t want to break my computer by dividing by 0, so we’ll move on.

Emissions

One of the main benefits of buses and trains that advocates will point to is reduced carbon emissions. Whether it be to protect the air quality of the neighborhoods in which they operate, or to help cities meet climate goals, buses and trains are held up as key alternatives to car, plane, and boat travel. But these heuristics aren’t always perfect. Hiroko Tabuchi, a New York Times climate journalist, found that her cross-country Amtrak trip generated more emissions than flying would have. Crazy! I know many have already done the math for buses compared to cars, but you’re here with me so let’s do it together. 

Emissions data is pretty accessible – the DoE even lets you compare cars side by side on a load of metrics, including emissions – so we’ll just compare the Smart Car, Suburban, and Bus’s CO2e rate per person. Like above, after the breakeven point, every additional passenger on the bus is increasing its lead. 

There are a few wrinkles, of course. Did you know you can get a diesel Suburban? I didn’t. I’ll include both the gas and diesel in my calculations. Also, the last Smart Car to be sold in the USA way back in 2019 was all electric. While the “long tailpipe” theory – that EVs are just as polluting as gas or diesel vehicles because they’re plugged into a dirty grid – is simply not reality, there are some emissions associated with an EV. These are called “upstream emissions” and are associated with the production of any fuel, whether that be fossil fuel or electricity. Upstream emissions can also be calculated with specificity to your own ZIP code and vehicle of choice by the DoE, so I’ll use upstream emissions with a Denver ZIP for everything involved.  

For the bus, I found that the average 40’ diesel bus (not the exact one RTD uses, but good enough) generates 2680 grams of CO2/mile in the Denver area, but couldn’t determine if this included upstream emissions as well. I’ll generate a conservative estimate including estimated upstream emissions to factor this in based on the upstream emissions we’re using for the diesel Suburban. I also found upstream emissions for an electric 40’ bus, so I’ll also consider this in case RTD ever adopts those. 

Here is everything in a chart: 

For the cars, we’ll divide those totals by the average passengers then compare each bus with each vehicle. 

To me, these results were fascinating. I had personally assumed that the bus would be far more efficient, but it seems like generally you need 7 or 8 people on the bus for it to be an environmentally wise decision. Of course, buses can carry far more people than that, but I’ve certainly been on buses where there were fewer than 7. One big takeaway from this for me is that I really hope Denver continues to invest in electric buses. EVs aren’t the solution to our climate woes, but where we have necessary vehicles (like buses), I’m all for them. 

Out of Pocket Costs 

Here, I am trying to figure out how many people need to be riding the bus for it to make sense from a cost perspective. There are a number of ways you might do this – average cost per mile driven, for instance – but I’m going to use “total cost of ownership”. Every car has a total cost of ownership, which is fuel, insurance, fees, and maintenance costs over the lifetime of the vehicle combined with the initial purchase price. Obviously, a bus has a way bigger price tag, more fueling costs, and costlier maintenance requirements. We’ll just assume we bought all of these cars outright rather than financing them, because I assume my readership is universally wealthy, and we’ll also assume a lifespan of 12 years for all vehicles in question. For consistency, we’ll also divide the cost of the vehicle by 1.7 people for the Suburban and 1.4 for the Smart Car people.  If we took those costs and divided them by ridership, when would we get breakeven with the Suburban or the Smart Car? 

US Department of Energy comes to the rescue yet again, here, as they supply a calculator to help estimate cumulative cost of ownership – they even include a nifty graph! I’m using estimates from all three of these websites to generate TCO estimates for the Suburban (diesel and gas) and Smart Car.

That Smart Car is going to be tough for our bus to beat! Based on this article, new 40’ diesel buses from Gillig (the manufacturer RTD uses), cost $517,000 each, while the EV options cost $988,311 (I’m not including any incentives in these calculations). For maintenance, I’ll use numbers from this document from PG&E (link will start a pdf download, fyi), whose assumptions I sanity checked against a few different sources and seem pretty good. This is how it looks for our diesel and electric buses:

High price tag! I was surprised to see the parity between diesel and electric, which really makes the electric case compelling for municipalities that have the upfront budget and adequate charging equipment (which was not included in these calculations). This is also pretty in line with this academic paper, once you revise the paper’s oddly low purchase price calculation. 

Now we can see how many riders it takes to break even – I’m not optimistic about the bus’ chances here but let’s find out. 

That is…shockingly good! Admittedly, most buses I am on do not have 31 people, but many of them have 20 people or more, meaning that societally we are better off all contributing our money toward buses rather than Suburbans to move people around economically in those instances. With all the incentives available for Electric buses, those numbers would look even better, provided the city has the facilities to charge and maintain electric buses. That said, this is the area where buses do the worst, which is why some commentators are quite critical of public transit, but public transit is a service and is not designed to turn a profit. 

Well, there you have it. Buses are a pretty great way to move people around, whether you’re worried about the space they take up, the emissions they produce, or the cost of the vehicles themselves. These calculations didn’t even take into account the cost of parking – both paid by the individual and the societal cost of allocating space for parking – the difficult-to-quantify safety benefits of buses, the benefits of providing transportation to people who may not be able to afford or may not be able to operate a private automobile, the reduced infrastructure costs, or the myriad other benefits that transit provides. Factoring these into the calculations would really give transit an upper-hand for all three categories. I’ll leave that for another post – this was a fun exercise, and has made me feel happier about my decision to be a transit rider. Perhaps these numbers will also assist you in your own transportation decision-making!