Preface. Weight reduces energy efficiency, so one way to make transportation more efficient is to light-weight rail cars, buses, trucks, and cars. For every 10% reduction in weight, up to 7.6% more fuel efficiency can be gained (Joost 2012). While a great deal has been done to lighten buses, cars and trucks, railcars aren’t replaced for decades.

So unless passenger rail cars are full, they can be the least energy efficient, even a passenger car with 4 people will carry more passengers per gallon.  This is often true, because the long trains running at rush hour continue to remain long as the time and cost to pay workers to shorten them mid-day is often not done.

Another issue with weight are that limits to growth in metals. Ore qualities are declining at the same time the energy to mine, crush, smelt, and fabricate metals is also in decline. The average weight of a vehicle in 1987 was 3,221, in 2022 it’s 4,156 pounds, with a Tesla Model X weighing almost 5,400 pounds.  And 3 billion more people are expected by 2050, and they’ll all want cars.

To get all the materials required, it won’t be long before we’re floating in outer space: by 2050, material consumption will need to almost triple to 180 billion tonnes of materials, almost three times today’s amount. If 180 billion tonnes grows in the future at 5% compound rate, in 497 years the entire earth will be consumed, all 5.972 x 10²¹ tonnes of it (Friedemann 2016).

When it comes to mass transit, efficiency is rated in people per gallon of gas. Full lighter-weight buses with diesel engines, which are nearly twice as energy efficient as gasoline engines, are the most efficient, and can be scaled up and down easily, and routed flexibly, unlike light rail.  Passenger rail cars are very seldomly replaced, the average U.S. Amtrak rail car is 21 years old today, in 2016 the average BART (bay area rapid transit) car was 40 years old.

What follows is based on the following document: NRC. 2015. Comparison of Passenger Rail Energy Consumption with competing modes. National Research Council, National cooperative rail research program, National Academies Press.

As the authors note in this paper “to date, decisions about train types and operating patterns in the passenger rail industry have not been strongly influenced by energy use and efficiency concerns”.

Alice Friedemann  www.energyskeptic.com  Author of Life After Fossil Fuels: A Reality Check on Alternative Energy; When Trucks Stop Running: Energy and the Future of Transportation”, Barriers to Making Algal Biofuels, & “Crunch! Whole Grain Artisan Chips and Crackers”.  Women in ecology  Podcasts: WGBH, Jore, Planet: Critical, Crazy Town, Collapse Chronicles, Derrick Jensen, Practical Prepping, Kunstler 253 &278, Peak Prosperity,  Index of best energyskeptic posts

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Since the 1970s, studies have always shown buses are more energy efficient than rail (and cars and airplanes).

After the 1973 and 1979 energy crises hundreds of energy efficiency studies were done, and hard to find since they’re stored as images not text (i.e. see May 1976 Bibliography for Transportation energy conservation, Transportation Center Library, Northwestern University, Evanston, IL)

Yet despite the inevitable decline of oil production, which probably started worldwide in 2018 for both conventional and unconventional, similar studies are rarely done today.  Nearly all papers today only care about greenhouse gas emissions.

One of these early studies by Mittal (1977) found if every seat had a passenger, a bus was by far the most energy efficient transportation mode (energy intensity BTU seat/mile):

Bus 500         Rail 1000         Compact car 1100         Average car 1600        Airplane  3600

A compact car comes close to being nearly as good as rail if all 4 seats are taken. When Mittal did this study, the average compact car had an average of 20 mpg.  But the best subcompact cars would have beaten rail since their combined 1977 city/highway miles per gallon were quite high: Honda Civic 44 (in 2016 at best 35), Honda Accord 42 (in 2016 at best 31), Toyota Corolla 41 (in 2016 at best 32), and so on (USDOE/AFDC 1977).

Based on actual ridership, rather than all seats filled, buses were still the most energy efficient, and compact autos (2.4 passengers) were even more energy efficient than trains:

Bus 1100, Compact auto 1900, Rail (Metroliner) 2000, Average Auto 2650, Rail intercity 3500, Airplane 6500

The Mittal study found that autos are most efficient from 50 to 60 mph.  But passenger trains reach peak energy efficiency at cruising speeds in the range of 20 to 30 mph, so to increase ridership and get people out of their cars, trains operate at faster, energy-inefficient speeds.

In 2016, buses are still more energy efficient than rail

Another reason rail tends to be less efficient than buses, or even autos, is that people usually need to drive to a train station, which adds to overall oil consumption.

This paper looked at other studies which I’ve summarized in Table 1. As you can see, buses perform on average 118% better than rail (from 24 to 218% better).   The numbers represent energy intensity in BTUs, so the lower the number the better.

And buses are better for other reasons — they can change routes, it’s easier to add more buses than to shorten and lengthen train cars.  In fact, in may passenger rail systems, it takes so much time, and so much money to remove rail cars during the day when there are few riders, that maximum length rush-hour trains run all day long, wasting tremendous amounts of fuel.

The best high-mileage cars would often beat rail as well, but since only average cars, with not-so-great miles per gallon were used in all of the studies, so I didn’t include autos, or airplanes, which are the worst wasters of oil by far.

Seat-miles per gallon (SM): ideal result: all seats are occupied.

Passenger –mile per gallon (PM): the actual energy efficiency given real ridership, also called the load factor, which is the average percentage of seats occupied by passengers.

Table 1. Energy intensity of bus versus rail

• Table 2-4. Energy intensity of intercity passenger transportation modes (Mittal 1977)
• Table 2-6. Energy intensity of Canadian passenger travel modes in 1996 (Lake et al. 1999)
• Table 2-9. Energy intensity of passenger modes—selected Canadian routes (English et al. 2007)
• Table 2-10. Emissions and energy intensity of passenger modes— selected routes in Spain (Alvarez 2010)

Passenger trains that aren’t full waste a lot of energy. Train-miles per gallon measures the overall energy efficiency of the entire train. With passenger trains, the heaver the train, the less energy efficient it will be.  The weight of passengers, even if the train is full, is usually not enough to make a difference.

Since locomotives and rail cars last 40 years, many mass transit systems are using heavy equipment that wastes fuel whether the train is full or empty.

When mass transit agencies are finally able to buy new equipment, the new locomotives and train cares are still heavy due to needing to comply with out-of-date rules on crash safety.  This prevents agencies from buying cheaper, lighter, safer, and far more energy-efficient European, Australian, or Asian equipment.

Buses have a hard time competing with rail when energy efficiency isn’t a priority

People find trains more pleasant, they often come with dome cars, bars, more comfortable seating, go faster, and have a smoother ride.  Who doesn’t love trains?  The middle class sees buses as lower-class and would prefer to ride trains – especially high-speed rail which would also get them to their destination faster.

Why electric train data was not included

As the authors note several times in this document:

“A tank or “meter-to-wheels” comparison [of electric to diesel-electric locomotives] ignores potentially significant losses associated with the generation and transmission of electricity from a remote generating site to the electric locomotive. The conversion of diesel fuel to energy for traction takes place on board the diesel-electric locomotive, so any losses that occur in conjunction with the conversion are incorporated into efficiency measurements. By contrast, losses associated with the generation and transmission of purchased electricity from a remote station to an electric locomotive occur before the electricity arrives at the train, so they generally are not reflected in measures of efficiency for the train. Measures of efficiency that are based on comparisons of the energy content of the purchased fuel to purchased kWh of electricity are thus skewed in favor of the electric train.”

The authors point out that under actual operating conditions, rather than the idealized coasting data used to get high-speed rail funding, electric trains tend to consume more energy than the statistics show: “Electrification does not generally improve passenger rail energy efficiency when direct and upstream energy consumption is considered, unless the regional generation profile contains a substantial amount of renewable power generation. When combined with track upgrades, implementation of higher horsepower electric locomotives may facilitate more rapid acceleration and higher operating speeds that actually increase energy consumption.”

Mittal looked at all-electric and diesel-electric energy intensity (BTU per seat-mile) at a steady cruising rate of 65 mph, and what the actual energy intensity would be when actually operating.  He found that the energy intensity of diesel-electric in real conditions increased from 35 to 85%, and all-electric increased from 164 to 229%.  The real figures for the all-electric locomotive would actually be much higher, since the calculation does not include the energy consumed by the power plant and lost over the transmission wires to the pantograph.

Hopkins also found the diesel-electric to be more energy efficient than the all-electric (115-170 seat-miles-per-gallon versus 65-95).

I also explain why diesel-electric locomotives are more energy efficient than all-electric locomotives in my book “When trucks stop running: Energy and the future of transportation” in the “Why electrify” section of “Can freight trains be electrified?”.

Conclusion

Conserving energy is only a priority in a crisis.  Meanwhile everyone’s been attending the all you can consume oil keg binge party since Spindletop first blew its lid.  It is human nature to party until the hangover begins rather than care or worry about future generations.

Some day, when fossil fuels are scarce and rationed, especially oil, people will wonder why such waste was allowed to happen.  Why wasn’t efficient mass transit built, mainly buses, to discourage cars, which guzzle 63% of transportation oil in the U.S.?  Why were CAFE standards abandoned for 30 years?

I’ve found two congressional hearings that discuss this.  In of them, Carole Browner, former head of the EPA describes her experiences in a mock exercise of an oil crisis (called the Oil ShockWave) where she played the role of the Secretary of Energy.  “In this position I was supposed to suggest a series of short-term steps that could be taken by the American public to reduce oil use. [So] I said we could impose a 55-mile per hour speed limit, which would save 134,000 to 250,000 barrels of oil a day, year-round daylight savings time to save 3,000 barrels per day, and a Sunday driving ban to save 475,000 barrels of oil per day.  The other Cabinet members  rejected these ideas. They did not think they would be acceptable to the American people.”

Carter also explains how it was in the interest of both oil and car companies to keep vehicles inefficient (Senate 111-78):

“We have gone back to the gas guzzlers which I think has been one of the main reasons that Ford and Chrysler and General Motors are in so much trouble now. Instead of being constrained to make efficient automobiles, they made the ones upon which they made more profit. Of course, you have to remember, too, that the oil companies and the automobile companies have always been in partnership, because the oil companies want to sell as much oil as possible, even the imported oil-the profit goes to Chevron and others. I’m not knocking profit, but that’s a fact. And the automobile companies knew they made more profit on gas guzzlers. So, there was kind of a subterranean agreement there”.

References

Friedemann A (2016) Limits to Growth? 2016 United Nations report provides best evidence yet. energyskeptic

House 110-19. November 7, 2007. Oil Shock: Potential for Crisis. U.S. House of Representatives.  52 pages.

Joost WJ (2012) Reducing Vehicle Weight and Improving U.S. Energy Efficiency Using Integrated Computational Materials Engineering. JOM volume 64: 1032–1038

Senate 111–78. May 12, 2009. Energy Security: Historical perspectives and Modern challenges. U.S. Senate committee on foreign