Re: [carfree_cities] More pollution from slower traffic
- Andras Toth wrote:
> Is it true or false that a car trapped in a traffic jam or slowedPerhaps the problem is the question. A better one might be, If the top
> 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?
speed were held down and more stop-and-go introduced to the driving
experience, would fewer people choose to drive, and would the use their
car in a more efficient manner?
The argument your question implies is part of a
favour-the-filthiest-mode thinking: whichever road users pollute the
most, given them a favoured postion on the road. In the name of
"safety," road engineers also argue that vulnerable road users must
yield to motorists who, after all, could kill them. In both cases, the
pedestrian and cyclist are restrained and, surprise-surprise, over time
their numbers decrease, with many of those trips switching to driving,
making the congestion-caused delays greater. Please note that there is
an ecology at work here.
Speed and delays are a product of conflicts on the roads caused by a
demands for the road's use. If you could make sure only one person
could use the road system at a time, voila!, no conflicts. But would
that be politically acceptable?
I am glad the wind friction was mentioned, since it suggests that the
premise itself is wrong.
And as far as the stop-and-go factor is concerned, in general, there are
more occasions-per-mile to have to stop or slow in a dense environment
than a less dense one, partly due to the smaller number of intersections
in each mile. But lower densities translate into longer distances for
each trip, more than wiping out any savings in reduced need to use the
brakes and gas-pedal.
One final note: speed is a _personal_ benefit to the driver, not the
community. As speed increases, the distanes between vehicles has to
increase proportionally, meaning that fewer drivers can be accommodated
at higher average speeds than at lower ones (and lane widths must be
higher, too). Also, increased speeds, as you have noted, increase the
seriousness of collisions, and they increase the marginal utility of
driving over walking/cycling/transit, not to mention the longer-term
effect of the increases in modal split cutting at the critical mass the
other modes need to be viable.