[sustran] Re: WorldTransport Forum Economics of Traffic Congestion
and TDM
Todd Litman
litman at vtpi.org
Fri Jul 22 01:30:14 JST 2005
Congestion costs, and the benefits of congestion reduction strategies, are
difficult to quantify because traffic congestion tends to maintain
equilibrium: efforts to reduce congestion by expanding roadway capacity
generally lead to increased peak-period vehicle trips, and little reduction
in delay over the long term. Much of the ultimate benefit consists of
improved access to urban-fringe locations, and therefore more sprawl, which
reflects a benefit to users but imposes various social costs. For
information, including extensive references, see "Congestion Costs"
(http://www.vtpi.org/tca/tca0505.pdf).
Most urban traffic models use fixed trip tables, which assume that the same
number of trips will occur regardless of travel speeds. As a result, they
fail to account for the additional peak period trips that occur when
roadway capacity increases (called "Generated Traffic," see
http://www.vtpi.org/gentraf.pdf). This type of modeling tends to overstate
the benefits of roadway capacity expansion and undervalue alternatives,
including public transit improvements and TDM programs.
Professor Richmond raises important questions about the evaluation of
travel time. Studies of the value of travel time savings (VTTS), have been
performed to evaluate travelers' willingness to pay for marginal reductions
in trip times (see "Travel Time Costs,"
http://www.vtpi.org/tca/tca0502.pdf). The are not intended to reflect the
full social value of a travel mode, particularly those such as Public
Transit and nonmotorized travel, which provide "basic mobility
(http://www.vtpi.org/tdm/tdm103.htm)." There is a much greater social
benefit to such mobility. An entirely different approach is needed to
quantify such benefits, which have nothing to do with users wage rates.
Improving poor people's access to medical services, education and
employment can provide large benefits to society, in terms of improved
health and increased productivity, as well as helping to achieve equity
objectives. For more information see: "Evaluating Public Transit Benefits
and Costs" (http://www.vtpi.org/tranben.pdf) and "Evaluating TDM Benefits"
(http://www.vtpi.org/tdmben.pdf)
Best wishes,
-Todd Litman
At 10:40 AM 7/21/2005 +0700, Jonathan E. D. Richmond wrote:
>There are important questions about what wage rate to use in these
>congestion measures if they are to be used in making decisions. The income
>of car owners is generally higher than those without cars, so in choosing
>who to give "benefits," calculations using income of beneficiaries will
>find that there is a greater "social benefit" from doing things that help
>the rich rather than the poor.
>
>This is one of the ways that expensive metro rail systems can be justified
>over simpler bus alternatives, for example: it is argued that they are
>more likely to take cars off the road, and the time savings to the former
>road users are valued highly. The social value of improving basic urban
>bus services for large numbers of people who depend on them is shown as
>far less, by comparison, because the poor earn only a fraction of the
>income of car users and their value of time is said to be much less.
>
>What do others think? Should we, in social decision making, regard the
>benefits to a poor person as worth less than those of a wealthier person?
>If so, what sort of methodological change does that imply?
>
> --Jonathan
>
>-----
>
>Jonathan E. D. Richmond 02 524-5510 (office)
>Visiting Fellow Intl.: 662 524-5510
>Urban Environmental Management program,
>School of Environment, Resources and Development
>Room N260B 02 524-8257 (home)
>Asian Institute of Technology Intl.: 662 524-8257
>PO Box 4
>Klong Luang, Pathumthani 12120 02 524-5509 (fax)
>Thailand Intl: 662 524-5509
>
>e-mail: richmond at ait.ac.th Secretary: Kuhn Vantana Pattanakul
> richmond at alum.mit.edu 02 524-6368
> Intl: 662 524-6132
>http://the-tech.mit.edu/~richmond/
>
>
>
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