Harun al-Rasyid,

Incorrect models or models incorrectly used have problems. I am convinced
that consistent equlibrium models (which are available in some places
nowadays) perform better than what you describe (for instance, building
more roads does not necessarily lead to less congestion, on the contrary,
as mode choice may change with the improvement, a new equilibrium is
reached where more people use cars and congestion may even end being
worse). The trouble is if you use inconsistent models (as most available in
practice) or if you do not have the ability or experience to interpret
correctly the model output (which is often not simple at all to judge).

One problem that current models do have though is that the sequence of
dcecisions does not matter (according to the model) while it certainly does
in practice. Think about implementing road pricing before or after
implementing substancial improvements to the public transport system.

Cheers,

J de D Ortuzar

A 06:04 PM 2/06/99 +0700, Harun al-Rasyid Sorah Lubis escribió:
>From: "Harun al-Rasyid Sorah Lubis" <[log in to unmask]>
>
>Most applied model in transport are non-structural and lack of feedback
>mechanisms.
>Therefore , we have to select some scenarios in order to predict the
>uncertainty of the future behavioural response. And partly problem of GIGO
>is one of the nightmare. A simple illustration of private vs. public
>transport strategy, i.e. building more roads (capacity) is predicted by the
>model to ease congestion, in fact what happen in the future is even more
>congested. This is explained, why this family of model is lack of feedback
>mechanism. Although, perhaps, other choice dimensions apart from route were
>considered, but how the construction and motorisation lobbies would took
>place during the time horison were out of hand.
>
>Feedback-rich model is belong to , some says, the system dynamics, which
>capable of telling the whole structure of the problem and their
>interactions. Maybe people recently involving in the policy analysis of
>transport and the environment could share their view on this issue. The
>reasons I asked this is due to the danger of using the non-structural model
>in a developing world problem, as delay of policy implementation may take
>place, high growth, etc. , apart from the basic problems of the lack of data
>base and lack of funding.
>
>
>
>Harun al-Rasyid S. Lubis http://trans.si.itb.ac.id
>Traffic Lab, Transport Engineering Division
>Dept. of Civil Engineering - ITB
>Jl. Ganeca 10 Bandung 40132 - Indonesia
>Tel/Facs. +62 22 250 23 50 [log in to unmask]
>
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Juan de Dios Ortuzar e-mail: [log in to unmask]
Departamento de Ingenieria de Transporte
Pontificia Universidad Catolica de Chile
Casilla 306, Cod. 105, Santiago 22, Chile
Tel: 56-2-686 4822 Fax: 56-2-553 0281


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