Loading ...
Sorry, an error occurred while loading the content.

More pollution from slower traffic

Expand Messages
  • Andras Toth
    Hello, As I am new to the list, I don t know whether this has been already discussed here (I searched the archive but did not find anything related). In
    Message 1 of 9 , Feb 6, 2002
    • 0 Attachment
      Hello,

      As I am new to the list, I don't know whether this has been already
      discussed here (I searched the archive but did not find anything related).

      In Hungary where I come from there is an argument popping up time and again
      about the harmful effect of slowing down the traffic. In many newspaper
      articles we can read that cars going slower pollute more, and therefore
      enlarging a road and building tunnels is justifiable and blahblah.
      And it is true, as we know that the right speed for optimal fuel
      consumption for a car is way over 50 km/h (not to mention 30 km/h). More
      fuel = more pollution.

      I can imagine a few counterarguments, but they are not entirely convincing
      to me.

      1. "Slower cars mean fewer cars. This counterbalances the increase in
      pollution per car." Has this been proved? Also, even if it is true we have
      to face the much more far-reaching and difficult argument about reducing
      the amount of car traffic, as some people would object that they do not
      want to be restricted in their access to the town.

      2. "Slower cars mean fewer accidents. Breathing in polluted air is not as
      bad as being hit by a car." But with this argument, how can you be an
      environmentalist and a protector of civil rights at the same time?

      3. "You can't live in a town turned into a network of highways." And their
      answer could be: "If that's the price to pay for less pollution, why not?"
      And then you have been dragged again into the tricky grounds of town
      aesthetics and social ethics etc. Isn't there a more straightforward and
      simple answer?

      How do you usually cope with this question?

      Regards

      Andras Toth
      currently in Paris
    • Mark Jaroski
      ... Frankly, it s simply not true at all. Yes, an engine has an optimum running speed, but it s measured in rpm (rotations per minute) *NOT* km/h. The car is
      Message 2 of 9 , Feb 6, 2002
      • 0 Attachment
        Andras Toth wrote:
        > In Hungary where I come from there is an argument popping up time and again
        > about the harmful effect of slowing down the traffic. In many newspaper
        > articles we can read that cars going slower pollute more, and therefore
        > enlarging a road and building tunnels is justifiable and blahblah.
        > And it is true, as we know that the right speed for optimal fuel
        > consumption for a car is way over 50 km/h (not to mention 30 km/h). More
        > fuel = more pollution.

        Frankly, it's simply not true at all. Yes, an engine has an
        optimum running speed, but it's measured in rpm (rotations
        per minute) *NOT* km/h.

        The car is polluting the least when it is parked with the engine off.

        Other than that the pollution curve has more to do with
        things like the temperature of the engine (a cold engine has
        to run a richer fuel mixture which generates soot).

        Speed has nothing at all to do with it.


        --
        --
        =================================================================
        -- mark at geekhive dot net --
      • carfreecrawford
        ... and again ... newspaper ... therefore ... More ... convincing ... we have ... reducing ... not ... The only way to speed up cars is to add road capacity,
        Message 3 of 9 , Feb 6, 2002
        • 0 Attachment
          Andras Toth said:

          >In Hungary where I come from there is an argument popping up time
          and again
          >about the harmful effect of slowing down the traffic. In many
          newspaper
          >articles we can read that cars going slower pollute more, and
          therefore
          >enlarging a road and building tunnels is justifiable and blahblah.
          >And it is true, as we know that the right speed for optimal fuel
          >consumption for a car is way over 50 km/h (not to mention 30 km/h).
          More
          >fuel = more pollution.
          >
          >I can imagine a few counterarguments, but they are not entirely
          convincing
          >to me.
          >
          >1. "Slower cars mean fewer cars. This counterbalances the increase in
          >pollution per car." Has this been proved? Also, even if it is true
          we have
          >to face the much more far-reaching and difficult argument about
          reducing
          >the amount of car traffic, as some people would object that they do
          not
          >want to be restricted in their access to the town.

          The only way to speed up cars is to add road capacity, which
          seems always to draw more cars, slowing things down again
          within a few years. You end up worse off than you started:
          more cars driving slowly.

          >2. "Slower cars mean fewer accidents. Breathing in polluted air is
          not as
          >bad as being hit by a car." But with this argument, how can you be an
          >environmentalist and a protector of civil rights at the same time?

          You're proceeding from the assumption that one has to accept
          dangerous, polluting objects on the street. Don't accept that
          basic assumption.

          >3. "You can't live in a town turned into a network of highways." And
          their
          >answer could be: "If that's the price to pay for less pollution, why
          not?"

          The answer is simply that you can't build your way out of
          congestion (and therefore out of pollution), and that trying
          to do so ultimately makes the situation even worse.

          >And then you have been dragged again into the tricky grounds of town
          >aesthetics and social ethics etc. Isn't there a more straightforward
          and
          >simple answer?

          Don't be afraid to argue this point, but I grant you that you'll
          only be likely to win your argument on the technical issues--
          people just don't seem to care about aesthetics any more. sign.
        • turpin
          ... You re half-right. Yes, engines have an optimum RPM, FOR A FIXED LOAD. But the load depends on the speed and the car. That doesn t answer the question of
          Message 4 of 9 , Feb 6, 2002
          • 0 Attachment
            --- In carfree_cities@y..., Mark Jaroski <mark@g...> wrote:
            > Frankly, it's simply not true at all. Yes, an engine
            > has an optimum running speed, but it's measured in rpm
            > (rotations per minute) *NOT* km/h.

            You're half-right. Yes, engines have an optimum RPM, FOR
            A FIXED LOAD. But the load depends on the speed and the
            car. That doesn't answer the question of how to make a
            trip in an automobile with minimum pollution. And if you
            ask THAT QUESTION, then it depends on the car as well as
            the engine. And for most cars, the answer is that you
            achieve minimum pollution per mile by driving at a steady
            rate, near highway speeds. The "steady rate" is the more
            important part of the answer. A car driven at a constant
            30 mph will use less gas and pollute less than one driven
            stop-and-go, though sometimes up to higher speeds. In
            fact, stop-and-go driving has a lot of harmful effects,
            not only in pollution, but also in wear and tear on the
            car, increase in accidents, etc.

            Now: there's always the issue of how important that
            fact is in relation to the variety of concerns at hand.
            But please, don't deny a fact just because it's
            inconvenient. It only hurts your credibility when you
            raise those other concerns.
          • Andras Toth
            Sorry, I managed to put a simple question very complicatedly, because I started to look for answers myself. So, putting aside all theoretical argumentation
            Message 5 of 9 , Feb 6, 2002
            • 0 Attachment
              Sorry, I managed to put a simple question very complicatedly, because I
              started to look for answers myself.

              So, putting aside all theoretical argumentation about traffic and urban
              planning (in which I have always fully adhered to the opinions you defend
              on this list):

              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?

              (I am secretly hoping that someone will come up with a reference to a
              scientific study proving what Mark Jaroski stated, that is speed has
              nothing to do with it.)

              Andras Toth
            • turpin
              ... 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
              Message 6 of 9 , Feb 6, 2002
              • 0 Attachment
                --- 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.
              • carfreecrawford
                ... urban ... defend ... down by ... doing the ... significant is ... Brake-specific fuel consumption of internal combustion engines generally reaches a
                Message 7 of 9 , Feb 7, 2002
                • 0 Attachment
                  Andras Toth continued:

                  >So, putting aside all theoretical argumentation about traffic and
                  urban
                  >planning (in which I have always fully adhered to the opinions you
                  defend
                  >on this list):
                  >
                  >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?

                  Brake-specific fuel consumption of internal combustion engines
                  generally reaches a minimum (optimum) at the engine RPM at which
                  the greatest torque can be developed. Generally, this is about
                  half the maximum RPM but varies quite widely. Further, the
                  fuel efficiency of a car in any gear is generally best when the
                  engine is running at the optimum RPM, but this is only for
                  that gear. The most efficient gear is alwyas the highest gear
                  except if steep hills are being climbed. That means that the
                  top gear of a car is always the most efficient and that a
                  speed of somewhere between 40 MPH and 65 MPH is almost always
                  the most efficient speed in top gear (some sports cars may
                  be most efficient at even higher speeds).

                  Aerodynamic dag of a car increases as the square of the speed,
                  so the energy required to overcome air drag over a given
                  distances doubles as the speed doubles. The rolling resistance
                  of pneumatic tires increases less slowly than the square law,
                  but, unlike railroad wheels, increases as speed increases due
                  to higher losses to hysteresis.

                  One of the largest terms in fuel consumption is acceleration
                  of the vehicle. This is because the energy used to accelerate
                  the vehicle is always lost when the vehicle brakes (except
                  that some hybrids recover a comparatively small proportion
                  of that energy). In stop-and-go traffic, poor fuel efficiency
                  is inescapable because the engine is idling some of the time
                  (using fuel without doing useful work) and is accelerating
                  the vehicle quite a lot of the time. When the vehicle must
                  brake, that energy is lost.

                  Thus, we see that a vehicle maintaining a steady 50 MPH is
                  almost certainly more fuel-efficient than a vehicle caught
                  in traffic. Fuel efficiency translates quite directly to
                  pollution output, with these caveats:

                  Cars equipped with catalytic converters emit far more
                  pollutants when cold than once warmed up. There are two
                  reasons: cold engines require much richer fuel mixtures
                  to run, and the converter does not "light" until it reaches
                  a certain, relatively high, temperature. Once this occurs,
                  the vehicle runs fairly clean.

                  When a car is accelerating, especially if the driver uses
                  a lot of power for a fast start, more fuel, and a richer
                  mixture, is required. This results in higher, and sometimes
                  MUCH higher, emissions levels.

                  So, there can be almost no arugment with the contention that
                  modern cars pollute less for a given distance when moving
                  in free-flowing traffic at highway speeds. (This equation
                  would change somewhat if engine power were limited to, say,
                  20 HP and top speed were limited to, say, 30 MPH; in that
                  case, a car moving a steady 20 MPH would be operating most
                  efficiently, and would, incidentally, be gettign FAR better
                  fuel economy than modern, high-powered cars.)

                  The argument against adding traffic capacity must thus be
                  made on other grounds, of which there is no shortage.

                  Hope this helps. For further info, see Mark's Handbook
                  (published under varying titles for many, many years, and
                  the standard reference for mechanical engineering).

                  Regards,

                  J.H. Crawford
                • Doug Salzmann
                  In a message sent Today, carfreecrawford wrote: - - Andras Toth continued: - - So, putting aside all theoretical argumentation about traffic and - urban
                  Message 8 of 9 , Feb 7, 2002
                  • 0 Attachment
                    In a message sent Today, carfreecrawford wrote:

                    ->
                    -> Andras Toth continued:
                    ->
                    -> So, putting aside all theoretical argumentation about traffic and
                    -> urban planning (in which I have always fully adhered to the opinions
                    -> you defend on this list):
                    ->
                    -> 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?

                    Joel and turpin have both provided accurate and fairly complete answers to
                    this question, the short forms of which are "yes" and "quite significant.
                    There is no question: they are correct.

                    However, the original inquiry was about the efficacy of increasing highway
                    capacity to alleviate congestion, based partly upon the assertion that
                    such action will reduce pollution by allowing autos to operate under
                    conditions that minimize tailpipe emissions. As has been pointed out
                    earlier in the thread, the phenomenon of induced traffic prevents such
                    reduction from being achieved in the real world.

                    A quick review should be sufficient to confirm that assertion. For
                    more than fifty years, autocentric societies have been madly adding to
                    highway capacity. Name one such society, or one metro area, where
                    increased capacity has resulted in overall reductions in tailpipe
                    emissions, longer than momentarily.

                    But cars don't belong in cities anyway. And they wouldn't belong even if
                    they were fueled by pleasant thoughts and emitted only music.

                    -Doug
                  • Chris Bradshaw
                    ... Perhaps the problem is the question. A better one might be, If the top speed were held down and more stop-and-go introduced to the driving experience,
                    Message 9 of 9 , Feb 7, 2002
                    • 0 Attachment
                      Andras Toth 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?

                      Perhaps the problem is the question. A better one might be, If the top
                      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.

                      Chris Bradshaw
                      Ottawa
                    Your message has been successfully submitted and would be delivered to recipients shortly.