4314Re: More pollution from slower traffic
- Feb 6, 2002--- In carfree_cities@y..., Andras Toth <toth_andras@y...> wrote:
> Is it true or false that a car trapped in a traffic jamYes, it is true. And you can prove it yourself. For a
> 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?
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
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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