Sunday, October 21, 2012

Does Public Transportation Save Energy?

Ever since the gas crises 1970's it's become environmental dogma that getting people to park their automobile and hop on a bus or a train will save energy.  In the 1970's, when American automobiles achieved 15mpg if they're lucky, that was certainly the case.  But a lot has changed since the 1970's.  How should the environmentally conscious traveler and urban planner think about transportation and energy use today?

The answer is complicated, but also surprising.  Let's consider local travel (commuting) and long distance travel separately.  Most of our transportation energy is consumed in local travel, so that is what we will consider in this article.  Long distance will have to wait.

Local Travel

Let's look at the typical energy use of some public transit systems, and then compare them to our favorite automobile in the driveway.  Let's look at the DOE Transportation Energy Data Book Chapter 2. Not surprisingly, public transit systems vary in their energy use: light rail systems use between 2,000 (San Diego, CA) and 30,000 (Kenosha, WI) BTU per passenger-mile.  Similarly, heavy rail systems vary from 1,800 (New York City) to over 10,000 (Cleveland, OH) BTU per passenger-mile.

How do we evaluate whether or not these systems save energy?  It depends on your perspective.  Let's suppose you're environmentally conscious and you drive a Prius.  Your rated 51mpg in the city translates to just 2,254 BTU per mile.  So even if you drive alone, you will be more fuel-efficient than all heavy rail (subway) systems except those in New York City, Atlanta GA and Oakland CA --- which are apparently only marginally more efficient than a single-driver Prius.  You will be more fuel-efficient than all light-rail systems except those in Stockon CA, Los Angeles CA, San Carlos CA, and Alexandria VA.  And you will be more fuel-efficient than all commuter-rail systems in America.

Now consider that US fuel economy standards are set to steadily rise, to 54.5 mpg (2110 BTU/passenger-mile) by the year 2025.  That means that by 2025, today's Prius will be below average in fuel economy, and everyone can expect to drive a car that's more fuel-efficient than all but a few transit systems.

Hmm... transit systems don't save energy?  How has it come to this, after we were told for decades that we should ride the bus to save energy?  Basically, busses and trains were always designed with fuel efficiency in mind, whereas that was not on the agenda for automobiles until recently.  Automobiles have been improving steadily, whereas there is not so much room for improvement on transit vehicles --- especially not electric ones.  Moreover, transit vehicles suffer from many inherent inefficiencies due to the nature of shared service: extra weight per passenger to make vehicles large enough to walk around in, frequent stops, and low seat utilization.

The last one is worth considering: a hypothetical morning rush-hour bus/train that starts in the suburbs picks people up along the way, and dumps a full load downtown will only have a 25% seat utilization.  That's 50% on the way in and 0% on the way back out.  So even if it's standing-room-only by the time you get off downtown, the average seat utilization of the system as a whole can still be relatively low.  On the other hand, automobiles have only a 25% seat utilization if you don't car-pool, which is not so different from what one could expect from a transit system.

So busses and trains aren't so much better as we were led to believe.  What should we do about this in our decision-making?  It depends on who you are and what decision you are making.
  1. If you're trying to get to work in the morning rush hour in a city with a crowded transit system, you will save the most energy by car-pooling.  Even if you only have a 30mpg Corolla, two of you in the car will still save energy over any transit system.  And by driving, you relieve the transit system of having to run more busses or trains.
  2. If you can't car-pool, just buy a Prius.  You'll still do better than almost any transit system.
  3. If you do a reverse commute, the things look very different: now you will save energy by taking transit --- and lots of it.  You are taking advantage of "free" seats that won't be filled anyway, making your effective energy use zero.

Carbon Footprint

Since I'm a climate scientist, I don't really care how much energy you use, as long as you didn't generate CO2 in the process.  What I DO care about is your carbon footprint.  So let's look at the comparative carbon footprint of these different modes.

From the carbon footprint point of view, automobiles aren't looking so hot anymore, nor are busses.  Why?  Because the only way we know how to power them is with carbon-intensive petroleum.  The New York City Subway, which runs on electricity, 30% of it nuclear-generated, now looks like a clear carbon winner over anything you can drive.  

Unless you drive an electric car, of course.  And aren't electric cars great: new cars such as the Chevy Volt and Nissan Leaf get anywhere between 100mpg and 200mpg equivalent, depending on who you ask and how your electricity is being generated.  Now, the efficiency winner tips back away from the transit systems.  Electric cars have the same carbon advantages over petroleum as do electric trains.  If nothing else, switching to an electric fleet will allow us to move away from petroleum for transportation, toward other cheaper primary fuels: for example, coal, solar, nuclear, wind, natural gas, hydro --- pretty much anything in the days of $100/barrel oil.

Smart Growth and Transportation Planners

What does this all this mean for city planners?  Rather than trying to build busses to the exurbs, it seems the best way to save energy on transportation is to decrease demand for it.  And we know how to do that: build denser, more compact cities where the places people live and the places they shop and work are closer together.  The term "Smart Growth" embodies this philosophy.

And it works.  Whereas transit usage is uniformly low almost everywhere, Total Vehicle Miles travelled per day varies greatly among American cities.  Not surprisingly, New Yorkers travel less than anyone else on average (9 miles/day): travel by any means is slow and difficult, and there is so much so close anyway.  And suburban New Yorkers, who drive through densely-packed suburbs, drive less than almost anyone else (17 miles/day).  Even Los Angelenos, famous for their car culture, don't drive that much: 23 miles/day.  In contrast, Houstonians drive an average of 38 miles/day.  Think about it: driving a Prius in Houston will have a greater carbon footprint than a Corolla in LA.  And if you live in New York City, you might as well drive a mini-van or SUV.

So where does transit come in?  The problem is, compact cities quickly become congested, and there's no place to park all those Priuses anyway.  Transit enables cities to grow at higher densities than would otherwise be possible using just automobiles.  Transit does not save energy directly.  But it is a key tool we have that allows us to save energy by building compact cities.  Even in "transit-oriented developments" being built today, the overwhelming majority of people drive.  But they drive less, and that is the key.

What does this mean for the transportation planner?  In building new cities, we should plan for transit via bus lanes, rights-of-way, etc.  But there's no need to actually build and operate the transit lines until congestion creates demand.  That is 180 degrees different from the more common approach today, in which we do anything we can to entice people out of their cars.  The problem is, once we've built a non-compact city, it doesn't matter what form of transportation we use to get around it, we will be stuck with high energy use.

There are other good reasons to build transit systems as well: they require lower capital costs for the vehicles, use less infrastructure per capita, use less land in the city centers, and provide universal mobility.  But they only really work well in relatively dense, compact areas.

The Ultimate Carbon-Friendly Transportation

If riding the bus doesn't win eco-points over driving your Prius, what's the serious eco-warrior to do to get to work?  The answer is the bicycle.  But not just any kind of bike.  Read on...

It's well-known that bicycles require less energy to move forward than any other vehicle known to mankind.  They are so efficient because they are extremely light-weight, they have low rolling resistance, and they don't go fast enough for that efficiency to be killed by their bad aerodynamics (25 mph and up).  So bikes are really efficient to push around, and twice as efficient as walking.

The big problem with bikes is their inefficient power plant: you.  Because you eat food grown through our commercial agriculture system, which is incredibly inefficient.  For example, 40 calories of fossil fuel energy are expended for every calorie of beef protein produced at your table, ready for you to eat.  Other foods seem to be better: grains require only maybe 10 calories of oil per calorie of food.

So when we take our agriculture system into account and look at biking vs. our trusty Prius, how do things  stack up in the end?  If you're a couch potato and need the exercise anyway, then the bike is a clear winner.

But suppose you're already fit, now you'll have to eat more when you bike.  If you eat bananas to power your bike, you'll apparently come in at 65g CO2 per mile.  That compares with 220g CO2 per mile for a Prius.  Definitely a lot more efficient.  But if you and your three buddies want to get somewhere, you'll do less harm to the planet driving your Prius.  And if you're a carnivore and love your cheeseburgers... well, you might as well just drive, the cheeseburger-powered bicycle apparently does 260g CO2 per mile.

If biking doesn't save much energy after all, what's the eco-conscious bike lover to do?  The answer is this new invention that came out of China over the last decade: the electric bike.  At first, it seems like "cheating:" surely a motorized vehicle will have a higher carbon footprint than a manual bicycle.  But our electric grid is (thankfully) far more efficient than our agriculture, giving electric bikes a significantly lower carbon footprint in the end.

All-in-all, my electric bike uses about 10% the power of a Nissan Leaf --- which translates into somewhere between 1,000 and 2,000 mpg electric equivalent.  The vehicle has a top speed of 20mph, goes for 30 miles on a charge, and requires so little power to recharge it's not worth metering: someone once e-biked across Canada using only $10 of electricity.

So there it is.  The electric bicycle is the most energy-efficient, lowest carbon-footprint way to get around that's known to mankind.  Eco-warriors, take note.  Even if you charge up your bike on the dirtiest coal-fired power you can find, your carbon footprint on an electric bike is still almost too small to measure.  Even better, e-bikes are blast to ride, and they get you across the Hudson River for free!


What are the take-away points for this, if you personally want to lower your carbon footprint?  It's pretty simple:
  1. Arrange your live so you don't have to travel as far.  See if you can live close to where you work, etc.
  2. Ride the bus if it saves you time, money or aggravation.
  3. Plan on spending $25K for your next car, which should be a hybrid and get at least 45-50 mpg, even in the city.  This is less than the average $30K spent on new automobiles in America today.
  4. Go get an electric bike, and ride it wherever you find it to be practical.  You will make the money back very quickly in lowered costs of gasoline, wear-and-tear, tolls, etc.
  5. Get involved in your local government to adopt a complete streets policy --- on that provides safe bicycle facilities in your town.
This article is Copyright (c) 2012 by Bob Fischer.  Unauthorized use and/or duplication of this material without express and written permission from this article is strictly prohibited. Excerpts and links may be used, provided that full and clear credit is given to Bob Fischer and The Jersey Biker with appropriate and specific direction to the original content.

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