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  1. joe says:

    This all assumes that people come first, and then mass transit comes later. What if we acknowledge that density of cities is endogenous (aka, density can be CAUSED by mass transit, and less density is caused by cars). If we acknowledge this factor, then your argument of diminishing returns doesn’t hold (along with most of the other calculations). Why do you think Houston is less dense than New York City? Because one had mass transit, and was built around it, and the other did not and it was built around the car.

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    • Praxis says:

      The pattern of diminishing returns from transit expansion has been demonstrated empirically. It just doesn’t attract enough people.

      Houston is less dense than New York City because it was built in the automobile age. New York is dense because it was built before the mass affordability of cars. Travel speeds were much slower, so buildings had to be closer together. There’ll never be another New York. Almost all new urban development will be low-density and car-oriented.

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  2. Bob F says:

    See the following article that came out a week before this one:


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  3. Bob F says:

    The energy benefit of transit is it allows you to build compact cities and still get people where they need to go. That has the effect of reducing travel needs for everyone, including the 80% who will still drive to work. As we build out new “Smart Growth” communities, we can build in a way to minimize travel distances — and then add transit service to the extent that congestion and demand warrants it.

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    • Praxis says:

      We could build even denser cities and walk or bike everywhere. That would save even more energy. But people don’t want to live that way. And they don’t want to live at transit-oriented densities either. Cars are just a much faster, more comfortable, more convenient and more practical way of getting around. That’s why they’ve displaced transit almost completely, and why for 50 years we’ve been designing our urban areas mostly for cars instead of buses and trains. The only urban areas where transit still has a substantial share of the transportation market are old dense cities like New York that were built before cars became widely available, and where driving (and parking) is difficult and expensive because of the lack of space.

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      • Gerry says:

        You are ignoring new development in communities like Portland, Minneapolis, and Denver. And how many people are jumping to move to these places versus Houston and Detroit? As a redisent of a small town forced to drive into the suburbs due to my job, I am very sick of people saying that this is some kind of choice that I am making.

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      • Praxis says:

        Most new development is low-density and car-oriented, not high-density and transit-oriented. That includes most new development in Portland, Minneapolis and Denver. The most recent Census data shows that the vast majority of growth in the U.S. is occurring in suburbs, not in dense urban cores or downtowns.

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      • Green Mountain Bot says:

        Minneapolis has had the largest total growth of any city in Minnesota over the last 10+ years, and Saint Paul is second. Some cities have had higher percentage growth, but in terms of bodies moving in, the core cities are ahead of the rest.

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  4. Frank says:

    It is tremendously refreshing to see an honest analysis of the relative costs and environmental impacts of public transit and private cars. Perhaps the evaluation can, in the future, be expanded to include the cost (value) of riders’ time spent traveling. I haven’t read other comments on this piece yet, but I can be sure it is filled with virulent anti-car rants filled with the transit fanatic’s trademark refusal to accept the facts.

    Thank you to Freakonomics for once again injecting fact into the discussion.

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  5. Chris Theis says:

    This story brings up one of my pet peeves, HOV lanes. In my narrow view of driving the streets of Denver it seems that HOV lanes create more congestion than not. I don’t think many drivers are changing their driving habits to take advantage of the HOV lanes, so the overall effect of the HOV lanes is more pollution.
    As I have sat in the traffic jams and watch the empty HOV lanes I have wondered if Freakonomics has had the audacity to disprove the efficiency of HOV lanes. I am sure politician, left or right will ever take this on.

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  6. Jei says:

    Your biggest mistake is that you assume the only place to add new transit is in low-density areas. With crush-loaded transit vehicles during rush hour, adding more vehicles easily increases ridership while remaining extremely efficient. Interestingly, mass transit probably follows the same rules as highway capacity–in certain markets, you can never build too much. Think about it, would you switch if the vehicles came every 3 minutes during peak? Wouldn’t everyone?

    The best incentives to ride transit is not actually the cost of driving vs. riding, but the time penalty. Transit has to take no more than 10-15% longer. Investments to make our transit faster than driving in markets where that is possible is also a good investment.

    Also, on an individual level, your choice to ride transit is always a carbon benefit. The marginal carbon cost of an additional passenger is very low.

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  7. Gerry says:

    The big factor not mentioned here is the development patterns that transit encourages. Consider Portland, OR, where dense development, with a small footprint, leads to lesser impact on the environment. Compare that to places like Houston and Detroit, developed around the automobile, where long commutes emit large amounts of pollutants and encourage land use that destroys the natural environment.

    As an electrical engineer, I take strong issue with the idea that electrification of automobiles is around the corner. While GM and Nissan have accomplished wonderful things with the Volt and Leaf, there is no sign that the economics of these vehicles will ever reach a point where a middle class family could afford two of them. Engineers do not magically invent more fuel efficient cars whenever policy makers snap their fingers, so the mandated increase in fuel economy standards is by no means a guarantee of tomorrow’s reality.

    Development patterns in these low carbon footprint cities- like New York, Chicago, and San Francisco, depend on transit. These cities simply would not exist as we know them without transit.

    Electrified transit is the proven technology that we have right now to drastically clean up how me move ourselves and develop communities. California’s bullet train, for example, is planned to operate with 100% renewable energy. We need to break the cycle of addiction, reject the temptation of questionable promises, and improve our country with what is already there for us- electrified transit.

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  8. Gary Hewitt says:

    There are three ways that public transportation can reduce carbon emissions:

    1) Reducing Auto Trips: This is only variable considered in your blog post.

    2) Reducing Congestion: Auto benefit from reduced congestion when public transportation is available. The reduced idling and travel time for autos reduce emissions.

    3) Allowing for Compact Development: The existence of public transportation allows compact development where walking and biking are possible. These reduced trips also have a positive impact on emissions.


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