Your basic concepts are right but I think your numbers are a bit off. No two
lane highway can carry 40,000 cars a day. The threshodl for congestion on a two
lane road is closer to 10,000. The other factor that has to be taken into
account is access control. A six lane with controlled access can carry 120,000,
albeit not very well. A six lane with frequent intersections can carry far
less. There are many examples around the nation of adding lanes to solve
congestion that only created more traffic and increased congestion. Possibly
the worst example is Atlanta, where its gotten so bad that air pollution and
traffic congestion has become the #1 political issue in the region. In Georgia,
the current Governor was elected on a campaign platform desigend to address
those issues.
As body was created that has veto power over new development that will agravate
the situation and also has the power to order local municiplaities and even
counties to accept new transit facialities that they have long opposed. In that
area the northern suburbs opposed tranist because it might make it possible for
"those people" to get to their county to go to work. Horrors! I suppose folks
had visions of burglars taking the subway out and hauling the TV's they had
stolen home on the train.
Carol Becker wrote:
> I had written earlier that we could not build enough highways to solve
> congestion. Someone challenged that assertion and asked for some facts.
> This is such a tenent of transportation planning that the folks that I asked
> were a bit thrown by the question. But they were able to give me a real
> live local example.
>
> Average daily traffic counts reflect the number of cars driving on a road.
> A rough rule of thumb is that a two lane highway carrying around 40,000 cars
> a day will be congested. A four lane highway around 80,000 a day, a six
> lane aroune 120,000 a day. These are rough numbers because what starts
> happening is that the peak hours begain to spread out. Rush hour instead of
> being from 7:00 am to 8:30 am becomes 6:30 am to 9:30 am and continues until
> you have the problem that Chicago has that the highways are congested even
> at 12:00 midnight. So roads can go over these rule of thumb numbers but
> mostly by adding hours of congestion.
>
> In 1986, Highway 12 was carrying 87,500 cars a day (measured right where it
> came into downtown before the I-94 exit). At the time, the road was clearly
> having congestion problems. This road was rebuilt from being a four lane
> signalled road to a six lane interstate highway at a cost of billions of
> dollars. In 1998, this same stretch was carrying 148,000 cars per day, also
> clearly congested. Simply put, we spent billions of dollars to take a
> congested road and replace it with a larger congested road. History and
> survey data shows that enough latent demand exists that if we widened it
> again, it would be congested again within a decade, possibly sooner.
>
> There are many factors contributing to this:
> - More people owning cars
> - Women entering into the workplace
> - Fewer people able to share a ride (rush hour auto occupancy is down to
> 1.19 persons per car) (it is so low that MnDOT has stopped surveying this)
> because their work places are located so far apart
> - People drive further to get to work
> - Many more people in the region with little additional construction of new
> highways
> - A pattern of sprawling development
>
> Given these societal factors, there is no solution to congestion. As long
> as we continue to develop the region like we have and we don't change our
> driving habits, we will have increasing congestion problems. There are
> three basic strategies to addressing it:
>
> - Increasing highway lanes to provide at least temporary relief and
> removing bottlenecks to make the existing highway system more efficient
>
> - Moving people into higher occupancy vehicles, whether they are car
> pools, van pools, buses, LRT, commuter rail, which preferably run in their
> own dedicated corridor like a dedicated busway or commuter rail so they
> don't have to be on the crowded highways
>
> - Having a different development pattern to accomdate the 20% population
> growth that the region is going to experience in the next 20 years,
> preferably one that is more compact and supports these alternative
> transportation methods.
>
> We are going to have to pursue all of these strategies if we are going to
> keep the region viable.
>
> Carol Becker
> Longfellow
>
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--
Caleb Faux, AICP
Pflum, Klausmeier & Gehrum Consultants
5533 Fair Lane, Cincinnati, Ohio 45227
(513)-272-5533 Fax (513)272-5522
email: [EMAIL PROTECTED]
web-site - www.pkgconsult.com
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