Reliability in Transport CBA : Comparing and Testing the Consistency of the Methods and Their Outcomes
David MEUNIER, LVMT (UMR-T 9403, École Des Ponts, IFSTTAR, UPEM, UPE), Hélène LE MAITRE, French Ministry of the Environment, Energy and the Sea, Nathalie PICARD, THEMA (université De Cergy-Pontoise)
We compare diverse reliability valuation methods, both qualitatively and by their quantitative results when applied to a list of projects, and discuss their consistency conditions.
The reliability issue in transport is discussed here as uncertainty in travel times.
Diverse methods are developed by researchers or used in practice for project CBA in a good number of countries, with valuation rules that translate a quantitative measure of the uncertainty into a monetary value.
In this paper we compare methods, as regards their general characteristics such as theoretical background, practicability and data requirements but also, using data on French networks, as regards their outputs i.e. how they hierarchize projects (ordinal classification) and how they value them.
The three families of methods considered are « mean-dispersion indicator », « proportion of late arrivals » (for public transport) and « compensatory variation ». This last one is calibrated using the MIMETIC survey. The parameters used for the other methods come from official guidelines or from a meta-analysis of values appearing in the literature.
A list of travel time distributions for 12 road and rail projects is used for the comparison.
As a whole, the results indicate that project hierarchies are consistent over the methods tested, but that the monetary values given may differ, especially for the public transport methods which show much bigger reliability valuations.
Since travel time data is usually available at the link level, the difficulties in treating travel time uncertainty at the Origin-Destination level as a chain of links are also considered, acknowledging that the assumption of independence between individual links is not realistic.
Theoretical issues are discussed such as the consistency with average travel time valuation, the influence of transport service operators’ actions in public transport, and the relationship between inter-consistency of the methods and the choice of the functional form of travel time distributions.
Association for European Transport