Another City is Possible: Cars and Climate

Last week I taught a class at the University of Colorado for a friend.  The class is entitled Another City is Possible: Re-Imagining Detroit. She wanted me to talk about the link between cars and climate change. As usual, I didn’t finish putting the talk together until a couple of hours before the class, but it seemed like it worked out pretty well anyway. In fact, I actually got feedback forms from the class just today, and they were almost uniformly awesome to read. As if I might have actually influenced someone’s thinking on how cars and cities interact, and how cities could really be built for people. It makes me want to figure out a way to teach on a regular basis.  Here’s an outline of what I said, and some further reading for anyone interested.

What is a car?

For the purposes of this discussion, when I say “car” I mean a machine capable of moving at least 4 people at a speed of greater than 80 km/hr (50 mi/hr). This means cars are big (they take up a lot of space) and cars want to go fast (though in reality they go at about biking speed on average, door-to-door, in urban areas). Cars as we know them today are also heavy, usually in excess of 500 kg (1000 lbs) and numerous, because they’re overwhelmingly privately owned. These four characteristics in combination makes widespread everyday use of automobiles utterly incompatible with cities that are good for people. Big, fast, heavy, numerous machines are intrinsically space and energy intensive, and intrinsically dangerous to small, slow, fragile human beings.

The Takeaways:

  • Tailpipe emissions are just the tip of the iceberg — the vast majority of the sustainability problems that cars create have nothing to do with what fuel they use, or how efficiently they use it. Amory Lovins’ carbon-fiber hypercars could run on clean, green unicorn farts, and they’d still be a sustainability disaster.
  • The real problems that come from cars are the land use patterns they demand, and the fact that streets and cities built for cars are intrinsically hostile to human beings. In combination, sprawling, low-density land use and unlivable, dangerous streets functionally preclude the use of transit, walking, and biking as mainstream transportation options. In a city built for cars, you have no choice but to drive.
  • The good news is that another city is not only possible, it already exists. Very modest density (about 50 people per hectare or 10 dwelling units per acre) is enough to drastically reduce car use, and make low energy transportation commonplace. In combination with good traditional urban design, these cities are extremely livable, healthier, cheaper to maintain, much more sustainable, and much safer than our cities.
  • The bad news is Peak Oil is not going to save us. There are a whole lot of unconventional hydrocarbons out there in the oil shale of the Dakotas, the tar sands of Alberta, the ultra-heavy crude of Venezuela’s Orinoco basin, and the ultra-deep water reservoirs off the coast of Brazil, etc. We’d be crazy to burn them all, but hey, maybe we’re crazy. And even if we did run out of oil, it’s entirely possible to electrify our cars for everyday urban use, even with today’s mediocre battery technology. If we want a different kind of city, we’re going to have to choose to build it.

Urban Form and Transportation Energy

The density of a city (citizens per unit area) has an enormous impact on how much energy people use to get around:

Urban Density vs. Transport-Related Energy Consumption
Urban Density vs. Transport-Related Energy Consumption

But you don’t have to have very high densities to dramatically reduce the amount of energy used. We’re not talking about the skyscraper canyons of lower Manhattan and Hong Kong. If the entire city is built to about 50 people per hectare — which is comparable to the density of Boulder in the downtown area, or on University Hill, suddenly cars become dramatically less attractive — they’re more difficult to use because parking and traffic congestion become serious issues, and they’re less necessary because at 50 ppl/ha you can walk to many destinations, and frequent, convenient mass transit service is economical. The 85% decline in energy use for transportation you see going from Denver to Amsterdam is there because many people aren’t driving at all, not because they’re using more efficient cars.

It’s about Time, not Distance

People are much more sensitive to how much time it takes to get to their destination than about how far they have to go to get there. On average, we’re willing to spend something like a half hour each way on a daily commute, regardless of how we make that commute. On average we’re willing to take about 5-10 minutes each way for the easy little everyday errands we run nearby. The consequence of this sensitivity to time, and not distance, is that if you build capacity for people to move faster, they do not hesitate to go further. Building additional freeway lanes and unimpeded arterial roads thus leads to sprawling land uses. Increasing capacity simply allows people to go ever further.  It’s easy to build cities that are dense rather than sprawling, and in which your commute takes the same amount of time but is more pleasant, and done at lower speeds under your own power.

All of the danger, none of the speed

Because you can’t build your way out of a congestion problem, congestion is endemic: the average door-to-door speed in the US if you’re driving in an urban area is only about 15 km/hr (10 mi/hr), which is pretty close to the speed of a mom riding a cargo bike carrying two kids and groceries in Copenhagen (their bike traffic lights are timed for 20 km/hr). In addition, the average US household spends more than $8,000/year on cars. If you think of all the hours that had to be worked to earn the money to pay for the cars as part of your travel time, then the real speed of a car often ends up being a lot more like walking.

About 12,000 of the 35,000 people killed by cars in the US each year aren’t in the cars — they’re pedestrians and cyclists. Since the 1950s, the safety of car occupants has increased dramatically, due to the introduction of seat belts, air bags, crumple zones, and anti-lock brakes. Meanwhile the safety of those outside the vehicle has declined, as our streets and cities have been built ever more with the convenience of drivers in mind, at the expense of everyone else. Unfair though that might be, biking and walking still aren’t actually that dangerous. Even with our poorly designed streets, a sedentary lifestyle is still far more deadly than getting out of your car. It is often the case that the extra time you need to spend to get where you’re going by walking or riding your bike is more than made up for (on average) by the increase in your life expectancy: i.e. it’s time you would have spent dead anyway, so if the walk or ride is pleasant, you’re certainly coming out ahead.

Free Parking Is Not Free

Parking is actually fabulously expensive. There are about a billion parking spaces in the USA. Each one costs several thousand dollars on average. Spaces in parking structures cost between $15,000 and $50,000 each! This means there are several trillion dollars invested, in the US alone, in storing cars when they’re not in use. Spread out over the lifetime of the parking spaces, that’s around $1,000 a year, for every single person in the US. Almost all of that cost is socialized — you never see it directly, but that doesn’t mean it isn’t there. If you live in an apartment or condo with a dedicated parking space in a structure or underground, that space alone costs you about $100/month. In some cities, parking takes up as much as 30% of the city’s land area.

Urban buildings use less materials and energy

Not only do slightly denser, walkable, bikeable, transit accessible cities use vastly less energy for transportation because they functionally preclude the widespread everyday use of cars, the buildings they’re made up of also use much less energy and materials.

LocationEfficiencyMulti-unit dwellings that share many interior walls are thermally much more efficient than single-family homes, because their surface area to volume ratio is smaller — they have less of their skin exposed to the elements per unit living space inside. This means they’re more energy efficient, and much cheaper to make very energy efficient. This is true because most of the work of making buildings efficient involves upgrading the building envelope — making them airtight and highly insulated. In the figure above from an EPA study entitled Location Efficiency: Boiling it Down to BTUs (the British Thermal Unit is an antiquated non-metric energy unit), you’ll note that on the far right, the small gray bar, representing a normal, not particularly efficient multi-family dwelling and a normal car in a transit rich area uses less energy than any of the other options to the left: putting green buildings and hybrid cars in suburban contexts is still more energy intensive than boring old apartments and condos with your average American gas guzzler in the city.

In addition to the buildings themselves being more energy and material efficient, compact development patterns use far less wire, pipe, and pavement — all their per-capita infrastructure costs and material investments are reduced.

Cars are Energy Intensive, Renewable Energy is Diffuse

Moving numerous, big, fast, heavy things long distances every day is energy intensive, no matter how you slice it. With fossil fuels driving those machines, this is a climate disaster, and today transportation accounts for about a quarter of our overall greenhouse gas emissions. With renewable energy backing electric vehicles, we can in theory address the emissions, but in exchange get a different monumental task, of supplying a vast amount of electricity from relatively diffuse energy sources. Reducing the energy intensity of our transportation systems makes the transition to renewable power much cheaper, easier, and less space intensive. Many countries (like the UK, or India) will have no choice but to eschew the high energy intensity lifestyles that we’ve become accustomed to in North America if they wish to rely on their indigenous renewable energy flows.

International Trade Will Continue, Flying May Not

When the energy intensity of transportation comes up, many people immediately start thinking about the enormous distances that we transport almost everything we make and buy, especially food. But it turns out that transporting cargo isn’t a very big problem. Container ships and rail are very, very efficient compared to passenger vehicles. Even long haul trucking, the least efficient major cargo transport mode, is still vastly more efficient than a single occupancy vehicle. At the most basic level, that’s because most of the mass that’s being transported in a cargo vessel is mass you actually want to move around, while in a car, more than 90% of the mass you’re moving is the car, not the cargo. If you count the mass of the driver as part of the vehicle (when you’re buying groceries you don’t actually want to go to the grocery store — you want the food to appear in your fridge), often more like 99% of the mass is vehicle, not cargo. Transportation of food accounts for only around 10% of its overall GHG emissions, and in the US, fully half of those transportation emissions are the result of the consumer driving the groceries home from the store.

Ironically, flying in a fully loaded passenger jet uses about the same fuel per passenger mile as driving in a Prius alone. The problem with flying isn’t that it’s particularly inefficient relative to driving, it’s that flying allows you to conveniently go several thousand miles in a single day. Many people in the US fly more miles each year than they drive, and those miles are roughly equivalent to miles driven on an emissions basis if you drive a fairly efficient car. There are lots of ways to make ground transportation much more efficient than it already is — lighter vehicles, electric motors, lower speeds, better aerodynamics, etc. But for flying, there’s just not much left that can be done. We might eventually double the fuel economy of a jumbo jet, but the nature of high speed powered flight is such that we’re not going to reduce it’s energy requirements by a factor of ten.

Low Energy Cities Can Provide High Quality of Life

Many people in the US will read what I’ve written above, and if they take me seriously or check the numbers, they’ll feel despondent, because it calls our way of life into question. But there are other ways of living, and some of them are actually much better, and available at much lower energy intensities. Cities that are built around the human scale — cities for people — can provide a very high quality of life at energies that are much more compatible with a stable climate.

A high quality of life is not the same as a high quantity of stuff. If you list off the things that really define a high quality life, it’s clear that they don’t require a lot of materials or energy. For example: autonomy and leisure time, clean drinking water, sufficient high-quality food, long life expectancy, low infant and maternal mortality, access to information and education, transparent and democratic governance systems, supportive family and community, etc.

Transportation is Just One Means of Access

Traffic engineers see transportation as a problem of moving cars. Many alternative transportation advocates like to talk about moving people rather than cars. We can also think of transportation as just one possible way to get access — to social and economic and recreational opportunities. But there are other ways to get access, including proximity: simply arranging to be in the same place as most of what you want access to, most of the time. Modestly dense cities with a diverse mix of land uses and opportunities close to each other make it easy to get what you want while only ever traveling short distances slowly. Good telecommunication technology also lets you access many opportunities remotely, using very little energy.

The Shape of Solutions

The solution to the energy intensity our urban transportation systems isn’t more efficient cars, it’s better cities. We need cities that merge the design elements that have made cities work as human habitats for thousands of years, with intelligent infrastructural systems that allow us make our economy far less material intensive, while still providing a joyful existence to around ten billion people, using no more energy than we do today. This is doable, if we want it. Many cities in northern Europe and Japan are already well on their way toward this goal.  They use about half as much energy per capita as we do in North America to provide a comparable quality of life.  If Zürich and Kyoto can cut their energy use in half again, taking them back to levels last seen in the 1960s, we’ll pretty much be there, assuming we choose to get that energy from carbon free sources.

This is not about making the right personal choices within the existing system. If you live in Houston or Tampa Bay or San Bernadino, you’re probably not biking or walking or using mass transit, and given the way those cities are built, that’s a rational decision. This shift is about changing our urban substrate, beginning with cities that already have good bones — taking places like central Portland, or Seattle, or San Francisco, or downtown LA, central Denver, Detroit, Saint Louis, Rochester, Chapel Hill, Boston — essentially any city that was built before the invasion of the automobile — and giving that space back to people wholeheartedly, in a livable form. If that can be done well, then the suburbs and exurbs will migrate inward, and the innermost ring of low-density developments built just after WWII can be re-built along the same livable urban lines. The outermost exurban fringes of our cities are likely impossible to save, and that will be difficult to deal with. Far more important than retrofitting the cities of the already wealthy nations, is getting urbanization right in places like Brazil, India, China, Mexico and the rest of the so-called “developing” world… which is rapidly becoming simply “the world”.  They need to create good cities from the beginning, rather than mindlessly replicating of our failed freeway utopias.

Additional Resources


  • Cities for People, a book by Danish architect and city planner Jan Gehl, about how to build cities on the human scale. Cities that are lively, safe, sustainable, healthy and economical, and that invite human beings to inhabit them joyfully.
  • Worldchanging 2.0: A User’s Guide to the 21st Century, a book edited by Alex Steffen, and compiled from the online magazine of the same name, laying out a vision in pieces of what a sustainable civilization looks like, and how we can get there today.
  • Carbon Zero: a Short Tour of Your City’s Future, a short e-book by Alex Steffen (available online at Grist) that talks about good cities as the platform upon which a carbon neutral civilization will ultimately be built.
  • The Death and Life of Great American Cities, by Jane Jacobs. One of the first books to really look at how people actually use cities on a day to day basis. She fought Robert Moses and his plans to build freeways through much of Manhattan, and won.
  • The High Cost of Free Parking, a book by Donald Shoup, examining the enormous hidden costs and effects of free parking, as provided in the US.
  • Fighting Traffic, a history of how cars came to dominate US cities in the early 20th century, and the public outrage that they initially inspired.
  • Sustainable Energy Without the Hot Air, a book by David JC MacKay, the chief science adviser to the UK office of Energy and Climate. It lays out in straightforward order of magnitude calculations what we use energy for, and what the various sources of renewable energy are, examining what it would take if we were really to make the transition to using them.

Talks and Films:

  • Climate Change Recalculated, a talk by MacArthur fellow and MIT physicist-entrepreneur Saul Griffith, given at the Long Now in San Francisco. He lays out just where all of the energy he consumes ends up going in all the facets of his daily life, and examines what amount of energy is actually required to lead a good life.
  • Sustainable Energy Without the Hot Air, David MacKay talking at Harvard about the material in his book.
  • Energy Transitions, a talk by Vaclav Smil about the drivers of environmental change, and just how hard it’s going to be to swap out our energy systems.
  • The Human Scale, a movie coming out in February 2013 by Andreas Dalsgaard about Jan Gehl style cities for people. It hasn’t been released in the US yet. Some clips are available from Gehl Architects on Vimeo, and the film has a page on Facebook.
  • Manufactured Landscapes, is a gorgeous and horrifying film about Canadian industrial landscape photographer Edward Burtynsky, who documents the effects of industrial society on the natural world and the people in it.
  • James Howard Kunstler critiques Suburbia at TED in 2004.
  • Alex Steffen spoke at TED in 2005 on the nature of a sustainable future, and then again in 2011 on how cities help us reduce all kinds of different environmental impacts.
  • Alex Steffen also spoke in Seattle over two nights (one, two) about bright green cities as a core climate solution before heading to the COP-15 talks in Copenhagen.
  • Jan Gehl speaking in Melbourne, Australia about Cities for People. About 90 minutes long.
  • The Social Life of Small Urban Spaces, an hour long film summarizing studies done in New York City in the 1980s that looked at how people actually use space in cities, and what makes public space vibrant and livable.
  • The Bicycle Dutch YouTube Channel, lots of videos showing how bike infrastructure in the Netherlands works, and what it feels like to live in a society that is both wealthy and not automobile dependent.


  • The Streetsblog Network, a nationwide association of blogs about the livable streets movement, and how our transportation and urban land use systems work, or don’t.
  • Streetfilms, hundreds of short online films illustrating livable streets solutions, from across the US and occasionally around the world.
  • Strong Towns, another blog on the benefits of livable cities, valuable because it comes from a much more conservative part of the political spectrum.
  • The Original Green, a blog that looks at the sustainable nature of very traditional urban development, over the last few thousand years, and how those same techniques can be used in modern cities.
  • The Atlantic Cities, a prolific blog about urban design issues from The Atlantic Monthly magazine. Lots of good pointers to other articles and studies.
  • A View from the Cycle Path, a blog written by largely by a British expat living in The Netherlands, on the nature of bike infrastructure that works to encourage mass cycling.
  • Copenhagenize, brazen urban bicycle culture advocacy from Copenhagen, Denmark. Lots of great pictures.

Related Stuff I’ve Written:

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Zane Selvans

A former space explorer, now marooned on a beautiful, dying world.

14 thoughts on “Another City is Possible: Cars and Climate”

  1. Excellent Article! Interesting, informative and very well written. I’ll be looking forward to more articles!

  2. I wouldn’t discount Houston: inside the 610 loop the population density is already about 25 ppl/ha (6500 ppl/ sq mi, – the big problem is how spread out things are outside the loop. It’s a situation very similar to LA and the Inland Empire & Orange County. If Houston METRO could get their act together and get some real public transit service going I’d bet they’d easily reach those levels of density you suggest before too long.

  3. Hi Zane, Hugh and I visited Stockholm last summer and if we were younger we’d be there now, permanently. It was so easy to get around and so liveable, along with those lovely islands, sigh. You’ve really tied it together with this article. We’re still looking for a community with this vision to retire to here. Jean

  4. I always like to quote an old buddy, and Boulder’s former director of GO Boulder before it was Go Boulder, Steve Clark:

    “Driving a car is like slicing butter with a chainsaw.”

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