Forwarded message:
From owner-tchrs@LISTSERV.ARIZONA.EDU Mon Jul 5 13:17 MST 1999
Date: Mon, 05 Jul 1999 13:29:19 -0700
From: Jane Jackson <jane.jackson@ASU.EDU>
Subject: math problem/freeways
Sender: Discussion List for Arizona Physics Teachers
<TCHRS@LISTSERV.ARIZONA.EDU>
X-Sender: jacksonj@imap1.asu.edu
To: TCHRS@LISTSERV.ARIZONA.EDU
Reply-to: Jane Jackson <jane.jackson@ASU.EDU>
Message-id: <v01510106b3a6c4b94b1c@[129.219.101.215]>
MIME-version: 1.0
X-MIME-Autoconverted: from quoted-printable to 8bit by listserv.arizona.edu id
NAA05102
Content-transfer-encoding: 8BIT
Content-Type: text/plain; charset=iso-8859-1
Content-Length: 6312
Phoenix and Tucson have something in common with Denver: a growing
population. Below is a commentary on freeways that Al Bartlett just sent to
me. Physics and math students could be assigned practical problems such as
this, so I share it with you.
Cheers,
Jane
********************************
ALBERT ALLEN BARTLETT
Professor Emeritus: Department of Physics: University of Colorado
Boulder, Colorado: 80309-0390
E-Mail: albert.bartlett@colorado.edu
July 5, 1999
Letter to the Editor
The Denver Post
Denver, Colorado
Via E-Mail
Dear Friends,
May I submit the following (approximately 880 words) in the hope that it
might be used as an OpEd piece in the Post?
ooooooo
WE NEED TO CHECK THE NUMBERS
The numbers in the Denver Post's front page story 'More Lanes, More
Traffic' ( June 28, 1999) raise three serious questions.
1) The story indicated that the present six-lane road ( I-25 ) can carry
256,000 vehicles a day 'if it is not widened.' Is this reasonable?
Let's do some arithmetic. This is approximately 43,000 cars per lane
each day, or an average of about 1780 cars per lane for each of the 24
hours in a day. This is about one car every 2 seconds in each of six
lanes. One can imagine cars at this density during the rush hours, but it
is hard to imagine this density 24 hours a day. Have I made a mistake or
are the numbers wrong in the story?
2) What is the public cost of the widening of I-25 per car accomodated
and per person transported?
The Post story said that widening would cost $650 million and 'would
bring 50,000 more cars a day onto that highway by 2020 .' As far as I
can tell, the 50,000 additional cars would consist of 25,000 cars
traveling to work in the morning and then returning home in the evening, so
that each commuting car is counted twice each day. If there are an average
of 1.2 people per car, the added 25,000 cars that are accomodated by
the lanes added to I-25 will get 30,000 additional people in to work in
the morning and home in the evening. To do this, it is proposed to spend
$650 million of public money. This is $26,000 for each commuting vehicle
or about $22,000 for each commuting person. This is an enormous public
subsidy for private personal transportation! This is just the initial
capital cost: maintenance is extra.
While the state and the federal government [i.e.,taxpayers] will pay the
cost of the added lanes on I-25, the local communities [i.e., taxpayers]
will have to pay for widening of local streets to get these extra cars onto
the new lanes on I-25 and then pay for widening streets to get them off
the new lanes. At the destinations one needs 25,000 new parking spaces
to accomodate all of these additional cars. These extra costs could easily
double the $26,000 cost per car of the added lanes, raising the total
cost of the public subsidy to $50,000 or more per car accomodated on the
lanes that are proposed to be added on I-25 . This should be of great
interest to fiscal conservatives, because we are talking about big money!
3) The Post's story told of debate over the projections for the future
growth of traffic on I-25. Are the projected figures reasonable?
The quoted increase from 256,000 to 306,000 vehicles per day by 2020
after the six lanes are increased to eight, corresponds to an annual
average growth rate of only 0.85 % . The total expected growth of the
commuting traffic is certainly greater than this. A front page story in
the Post (June 30) gave figures from which one can calculate that, in the
last eight years, the average annual population growth rate of Parker is
about 12.9 % and of Castle Rock is about 6.6 % . The following table
shows how a traffic load of 256,000 cars a day in 1999 will grow in the
years up to 2020 for 1 % , 5 %, and 10 % annual growth rates.
1999 2010 2020
1 % 256,000 286,000 316,000
5 % 256,000 444,000 732,000
10 % 256,000 769,000 2,091,000
Apparently the two lanes added to I-25 will take 50,000 daily car trips
out of the surrounding neighborhoods and this will fill the enlarged I-25
to capacity, but will it relieve the congestion on I-25? One planner made
the understatement, '[Even with the new construction] Congestion [on I-25]
isnít going to improve dramatically.' If we take 50,000 daily car trips
out of the surrounding neighborhoods and put these cars on the enlarged
I-25 , how long will it take for population growth to generate 50,000 new
daily car trips which then will have to go back into the surrounding
neighborhoods, leaving the neighborhoods no better off than they are today?
The total daily car trips could grow from 306,000 to 356,000 in 15
years if the annual growth rate of cars is 1 % , 3 years for 5 % , and
1.5 years for a growth rate of 10 % . It was said that the added lanes
will not reduce congestion on I-25 . With continued population growth,
the added lanes will not reduce the burdens the surrounding neighborhoods
suffer because they have to accomodate the spillover traffic from I-25. So
whereís the gain?
As quoted in the Post's story, Representative Todd Saliman understands the
problem. He observed that the projected traffic numbers are probably low.
He said, 'I know that people wish we could just add a few lanes and our
problems would be solved forever... But that's just not how it works.'
The general conclusion is, that as long as population growth continues in
the Metro Denver area, adding more lanes on major thoroughfares will not to
alleviate traffic jams, it will only enlarge the traffic jams.
Unless I have made a dumb mistake in my figures, I think the numbers given
in the story in the Post are not reasonable.
Sincerely yours,
Albert A. Bartlett; Professor Emeritus of Physics
University of Colorado, Boulder, 80309-0390; (303) 492 7016
************************************
Jane Jackson, Dir., Modeling Workshop Project
Box 871504, Dept.of Physics, ASU, Tempe, AZ 85287
480-965-8438/fax:965-7331. http://modeling.la.asu.edu
"The ideals which have lighted my way, and time after
time have given me new courage to face life cheerfully,
have been Kindness, Beauty, and Truth." - Einstein (1931)