Site icon Andy May Petrophysicist

Commuting to work: car, train or bus?

By Andy May

The United States Department of Transportation tells us in their online report “Public Transportation’s Role in responding to Climate Change” that we should use public transportation to reduce our greenhouse emissions. This claim is also made in Time’sGlobal Warming Survival Guide.” Even the CDC (Centers for Disease Control and Prevention) recommended public transportation, in 2017, as “one of the best ways to reduce greenhouse emissions.” Public transportation does reduce congestion during peak traffic hours, but data from the National Transit Database suggests that cars are cheaper and use less fuel per passenger-mile traveled, so this claim is suspicious. Let’s examine it.

An APTA (American Public Transportation Association) report says:

“A single person, commuting alone by car, who switches a 20-mile round trip commute to existing public transportation, can reduce his or her annual CO2 emissions by 4,800 pounds per year, equal to a 10% reduction in all greenhouse gases produced by a typical two-adult, two-car household. By eliminating one car and taking public transportation instead of driving, a savings of up to 30% of carbon dioxide emissions can be realized.”

Even the Federal Transit Administration, an agency of the U.S. Department of Transportation, says something similar:

“If just one driver per household switched to taking public transportation for a daily commute of 10 miles each way, this would save 4,627 pounds of carbon dioxide per household per year—equivalent to an 8.1% reduction in the annual carbon footprint of a typical American household.”

These quotes are so misleading, I’m tempted to call them criminal. Pay particular attention to the wording, especially “single person” switching to “existing public transportation” or “eliminating one car.” Wow! They framed that precisely, didn’t they? It’s a classic strawman fallacy.

Let’s examine the thesis in a more honest, straightforward and clear way. The goal is to transport people from home to work and back again. Is public transportation (bus or train) cheaper and does it use less fuel than driving in a personal car? We can save emissions (both greenhouse gas and true pollutants) by switching to natural gas or by using less fuel. A few transit buses use natural gas, but most use diesel, most light rail systems use electricity. Electricity is not very efficient, since only 32% of the primary energy used to produce it is delivered to the customer as electricity according to the EIA. Further, 30% of the electricity in the U.S. comes from coal, the dirtiest fuel according to the EIA. So, we will focus on the quantity of fuel used by cars, buses and light rail and the cost of each per passenger-mile.

Full disclosure, although I’m currently retired, I commuted to work by bus from 2008 until I retired in 2016. The decision to take the bus was not because of cost, although that helped. My company would either pay for the bus pass or parking and since the park-and-ride was a six-mile commute from my house and parking there was free, the bus was clearly cheaper for me personally. But, the main reason was to avoid almost two hours of driving every day.

Jeff Foxworthy, the redneck comedian, once said (paraphrasing): If you’re going 80 mph on the highway and every other car on the road is passing you, you’re in Houston on the Hardy Toll Road. The joke is a little old, today you could be on any of the Houston Toll Roads and the joke would still be true. Riding the bus was a relief, it was quality time to read or nap on the way to work and decompress on the way home. I enjoyed the bus ride and saved money at the same time.

But what about the cost to the community and the economy? The web site “Portland Facts” provides us with the data used to construct Table 1, which shows the total cost of commuting by personal car, light rail train and bus in 2007, in 2016 dollars:

Table 1. The passenger-mile cost of commuting by car, transit bus and automobile in 2007, in 2016 dollars. Source: Portland facts, AAA and the National Transit database (NTD).


Table 2 uses more recent data from the National Transit Database to show the same costs in 2016. Over the 9 years between the tables, the Toyota Corolla fuel use and cost per passenger-mile has stayed the same, light rail is now cheaper, but uses more fuel per passenger-mile (31.6 MPG versus 35.9 MPG) and the transit bus is more expensive but uses less fuel per passenger-mile (38 MPG versus 30 MPG in 2007). Both tables are in 2016 dollars, none of the costs are corrected for the difference in fuel prices. For those interested, the dollars in 2007 are 86% cheaper than the dollars today, that is the 2007 costs are multiplied by 1.16 to get to 2016 dollars.

By way of comparison, gasoline was about $2.40 in 2016 and $2.90 in 2007, but this difference is not considered in the tables. The miles-per-gallon values are computed by converting the volume of fuel used by buses and trains to BTU equivalents and then converting the BTUs to gallons of regular unleaded with 10% ethanol (E10 gasoline). The buses and trains use a variety of fuels, compressed natural gas, electricity, diesel and gasoline depending upon the city, but these can all be converted to BTUs of energy.

Natural gas, diesel and gasoline are primary sources of energy and their BTU equivalents are taken from this table in Wikipedia. Electricity is a secondary source of energy, the energy is created using coal, natural gas, nuclear or some other primary source and then transmitted to the end user for use. Creating electricity and transporting it involves a lot of losses and, on average, only 32% of the primary energy is delivered to the end user as electricity according to the EIA (see here for a discussion). For this reason, we used 10,666 BTUs per kWh to convert the electricity used by some light rail trains to gallons of gasoline equivalent, rather than the 3,413 given in the Wikipedia table. This is so the comparison of electricity to diesel, etc. is valid. Using this conversion factor, we are comparing the primary energy used to create the electricity to the primary energy used in diesel, natural gas or gasoline powered trains and buses, i.e. primary energy to primary energy.

Table 2. The passenger-mile cost of commuting by car, transit bus and automobile in 2016. Source: AAA and the National Transit database (NTD).


The automobile costs are from AAA brochures Your Driving Costs for 2007 and 2016. The values for light rail and transit bus costs are averages for the top ten systems in the National Transit Database (NTD), by size, in the U.S. The top 10 transit bus systems are listed in Table 3, the data shown is 2016 data. The spreadsheets used to make the tables in this post can be downloaded using the link at the end of the post.

Table 3. Some of the critical data from the National Transit Database for the top 10 transit bus systems in the U.S. Source NTD.


The top 10 light rail systems are listed in Table 4 along with some statistics. All the light rail systems listed are powered by electricity. Light rail lost riders between 2007 and 2016, but it did become cheaper.

Table 4. Some of the critical data from the National Transit Database for the top 10 light rail systems in the U.S. in 2016. Source NTD.


Table 5 shows the same data for the top 10 transit bus systems. Most of the transit buses are powered with diesel, but some are powered by natural gas, gasoline or electricity. Unlike light rail, transit buses have become much more fuel efficient and they have not lost riders.

Table 5. Some of the critical data from the National Transit Database for the top 10 transit bus systems in the U.S. in 2016.  Source NTD.


The average number of passengers transported in a car trip is 1.59, as shown in Figure 1, this translates to about 40% of the passenger capacity of a Toyota Corolla. The Toyota gets about 36 MPG, so the per-passenger miles-per-gallon is about 57 MPG of regular unleaded E10 (Ethanol 10%) gasoline, as shown in Table 1.

Figure 1. Average occupancy of various passenger vehicles. Source: (Davis, Diegel and Boundy 2010). See page 8-10.


The NTD database supplies us with the amount of fuel used in the various light rail systems and transit bus systems. In Table 4 we see that the average light rail system gets 31.6 miles per gallon per passenger mile in 2016, this is 45% less than the miles per gallon obtained from a Toyota Corolla. The number of passengers per train is determined from dividing the passenger-miles from the NTD database by the vehicle revenue miles. By comparing this to the seating capacity in the train we see that, on average, these trains run at only 13% capacity. This is the reason for the poor mileage per passenger-mile.

In Table 5 we see the same figures for the top 10 transit bus systems in the U.S. Transit buses get even fewer passenger-miles-per-gallon than light rail systems in 2007, but much more in 2016. However, transit buses still only get 66% of the passenger miles-per-gallon of a Toyota Corolla. Again, the reason is low seat utilization.

Discussion and Conclusions

There is no question that transit buses and light rail systems reduce highway congestion. Just two passengers on a bus or train remove a car from the roads on average. Transit buses and light rail are most heavily utilized during rush hour, so when traffic is heaviest, they remove the most cars from the road. This is a big plus. Transit buses utilize existing roads, but light rail systems require the building of exclusive, new infrastructure. The data in Tables 1 and 2 clearly show that the problem with light rail is the large capital expenditure required, relative to cars and buses.

In 2007, the light rail systems discussed in this post cost 185 million dollars more than the transit bus systems. The light rail systems, in terms of capital costs, which are the tracks, depots, maintenance buildings and facilities, and trains basically, cost $0.98 per passenger-mile in 2007. By way of contrast, the transit bus systems only cost $0.18 per passenger-mile and the Toyota only cost $0.27. The transit bus systems only purchase the buses, land and buildings for the park-and-rides, they use existing roads. The light rail systems get 20% more miles-per-gallon per passenger-mile in 2007, but passenger cars do better on fuel than both public transportation systems. Transit bus fuel economy improved by 2016 and in that year, buses were more efficient that light rail. Further, the light rail systems run with fewer occupied seats, they are not as flexible in scheduling as transit buses. The data shows that the transit buses provide more flexibility, lower start up costs, and lower net traffic congestion than rail.

Transit buses typically have more stops, in more places than trains. Thus, passengers travel fewer miles to get to a bus stop than to a train stop. In some cases, passengers can walk or bike to a bus stop, but very few people live close enough to a train station to get there by walking or bicycle.

It is obvious from the NTD and AAA data, that personal passenger cars are the cheapest and most environmentally friendly way to transport people to work. They use less fuel per passenger-mile and the costs are much lower than for transit buses and rail. But, cars cause more congestion than public transit. The NTD data shows clearly, that transit buses are a cheaper and more convenient (to the passenger) way to transport large numbers of workers during rush hour. Light rail might be useful in some circumstances, for example transporting passengers from one large population center to a downtown work area, but since American cities tend to be very spread out, it seems more likely that transit buses are the best option for most cities. The reason to use public transportation is to reduce congestion, not to reduce greenhouse gas emissions or air pollution.

The 2007 and 2016 NTD databases and some derivative datasets used to make the tables and illustrations in this post can be downloaded here.

Work Cited

Davis, Stacy, Susan Diegel, and Robert Boundy. 2010. “Transportation Energy Data Book: Edition 29.” Oak Ridge National Laboratory.


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