Improving Transport Project Appraisals
In the Islamic Countries
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1. Consider if the policy proposal has significant environmental effects
2. Detailed qualitative assessment to determine the range and nature of the environmental
effects identified
3. Make use of ecosystem services framework to define wider environmental effects
4. Quantifying and valuing environmental/ecosystem service effects
5. Report the environmental effects in the main policy appraisal
The appraisal period used is 60 years. A discount rate of 3.5% is used for the first 30 years, and
a discount rate of 3% is used for the remaining 30 years. Regarding risk analysis, there is no
prescriptive advice and it is just recommended to undertake a risk analysis.
2.2.5 Demand analysis
To support the development of evidence required in CBA, WebTAG provides guidance on
modelling techniques alongside the guidance on appraisal. It covers subjects such as forecasting
future levels of demand and modelling the impacts that a proposal will have on travel choices
such as route choice, choice of destination and choice of mode.
In TAG Unit M1 – Principles of Modelling and Forecasting28, it is explained why variable demand
modelling needs to be considered in an appraisal. Assuming that there is a need, it then goes on
to give initial advice on the scope of the model, with a view to develop a model which is
appropriate for the complexity of the interventions that it will be used to test.
In TAG Unit M2 – Variable Demand Modelling 29, considerations and processes required in
variable demand modelling are described. It includes the following items:
 Scoping the need for having a variable demand model and scoping out the requirements of
the model
 Travel costs handling within the model
 Development of the model
 Calibration of the model
 Ensuring validity of the model
2.2.6 Results of project appraisals
Appraisal is used to inform decision-makers throughout the development of a project, from the
early stage of alternative generation to the final approval. By providing those responsible for the
project with a means of identifying, designing, selecting and refining options, the appraisal
process avoids being no more than a hurdle over which the chosen alternative has to jump.
Different scenarios are used in the appraisal. The core scenario, based on the most unbiased and
realistic set of assumptions, will form the basis for the analysis reported in the Appraisal
Summary Table and, as such, should represent the best basis for decision-making given current
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