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4314Re: More pollution from slower traffic

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  • turpin
    Feb 6 5:28 PM
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      --- In carfree_cities@y..., Andras Toth <toth_andras@y...> wrote:
      > Is it true or false that a car trapped in a traffic jam
      > or slowed down by sleeping policemen pollutes more on a
      > given distance than a car doing the same journey at an
      > optimal speed/rpm whatever? If true, how significant is
      > the difference?

      Yes, it is true. And you can prove it yourself. For a
      given car, a good first-order measure of how much it
      pollutes on one trip compared to another trip is the
      ratio of gasoline burned on the two trips. The more
      fuel burned, the more pollution emitted. How much does
      your mileage improve when driving on the highway, over
      driving on the city? For most cars, it's quite a bit.
      If you look, you will find articles on the optimum
      driving for gas mileage, and this is close to optimum
      driving to minimize pollution. A typical car will
      get the the best mileage by being driven at a steady
      speed somewhere around 45 mph. It varies from vehicle
      to vehicle, as does pollution per gallon burned.

      "First-order measure." In fact, the pollution increase
      from stop and go traffic is even worse than reduced
      gas mileage indicates, because a car starting from a
      dead stop generates more pollution per gallon burned
      than the same car cruising at steady speed. (Some
      decades ago, I programmed engine control computers for
      Ford.)

      Of course, the pollution generated by walking or
      bicycling is MUCH less than by driving! The question
      asked is far from the only, or even the primary, factor
      in urban planning, or even in figuring out how to
      minimize pollution. Asked that way, yep, it's true.
      Don't try to buck the facts. But don't let one narrow
      fact distract from other issues.
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