How uncertainty in input and parameters influences transport model: output A four-stage model case-study

Manzo, Stefano, Nielsen, Otto Anker and Prato, Carlo Giacomo (2015) How uncertainty in input and parameters influences transport model: output A four-stage model case-study. Transport Policy, 38 64-72. doi:10.1016/j.tranpol.2014.12.004

Author Manzo, Stefano
Nielsen, Otto Anker
Prato, Carlo Giacomo
Title How uncertainty in input and parameters influences transport model: output A four-stage model case-study
Journal name Transport Policy   Check publisher's open access policy
ISSN 0967-070X
Publication date 2015-02-01
Sub-type Article (original research)
DOI 10.1016/j.tranpol.2014.12.004
Open Access Status Not Open Access
Volume 38
Start page 64
End page 72
Total pages 9
Place of publication Kidlington, Oxford, United Kingdom
Publisher Pergamon Press
Language eng
Formatted abstract
If not properly quantified, the uncertainty inherent to transport models makes analyses based on their output highly unreliable. This study investigated uncertainty in four-stage transport models by analysing a Danish case-study: the Næstved model. The model describes the demand of transport in the municipality of Næstved, located in the southern part of Zealand. The municipality has about 80,000 inhabitants and covers an area of around 681 km2. The study was implemented by using Monte Carlo simulation and scenario analysis and it focused on how model input and parameter uncertainty affect the base-year model outputs uncertainty. More precisely, this study contributes to the existing literature on the topic by investigating the effects on model outputs uncertainty deriving from the use of (i) different probability distributions in the sampling process, (ii) different assignment algorithms, and (iii) different levels of network congestion. The choice of the probability distributions shows a low impact on the model output uncertainty, quantified in terms of coefficient of variation. Instead, with respect to the choice of different assignment algorithms, the link flow uncertainty, expressed in terms of coefficient of variation, resulting from stochastic user equilibrium and user equilibrium is, respectively, of 0.425 and 0.468. Finally, network congestion does not show a high effect on model output uncertainty at the network level. However, the final uncertainty of links with higher volume/capacity ratio showed a lower dispersion around the base uncertainty value.

Results are also obtained from the implementation of the analysis on a real case involving the finalization of a ring road around Næstved. Three different scenarios were tested. The resulting uncertainty in the travel time savings from the comparison of the three scenarios expressed in terms of coefficient of variation, turned out to be between 0.133 and 0.145, thus confirming the importance of uncertainty analysis in transport policy assessment.
Keyword Demand modelling
Four-stage model
Q-Index Code C1
Q-Index Status Provisional Code
Institutional Status Non-UQ

Document type: Journal Article
Sub-type: Article (original research)
Collections: School of Civil Engineering Publications
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Citation counts: TR Web of Science Citation Count  Cited 4 times in Thomson Reuters Web of Science Article | Citations
Scopus Citation Count Cited 5 times in Scopus Article | Citations
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