Edinburgh Napier University

  Microsimulation modelling is a widely accepted tool in the assessment of the impact of a wide
variety of transport schemes. The robustness of a model depends on the accuracy with which traffic behaviour is
represented. In the case of road pricing the key element lies in predicting motorist’s behavioural responses when
confronted with tolls. This behaviour is affected by an individual’s willingness to pay to avoid a congested trip
that will result in either increased journey times (measured as ‘value of time’) or a more variable journey time
(measured as ‘value of reliability’). This “subjective value of time” differs from the “social value of time”
applied in project evaluation and which reflects the losses to society as a whole derived from longer travel times.
Firstly, this paper reviews subjective values of time and reliability from a variety of schemes from around the
world and finds that both VOT and VOR depend on a number of factors including the motorist’s socioeconomic
characteristics and the characteristics of the trip itself. Accounting for this heterogeneity is important in
forecasting usage in the context of tolls. Secondly, this study will attempt to derive VOT and VOR values in a
UK context. In the UK there is only one toll road, the M6Toll, which runs parallel to the heavily congested M6
around Birmingham. A Paramics microsimulation model of both roads has been developed, calibrated and
validated using traffic data from the Highways Agency’s Journey Time Database. By comparing results after
each historical toll rise on the M6Toll, this model will serve to derive VOTs and VORs suitable to the UK
context. These values will then be used to develop a new form of the cost equation that governs vehicle
behaviour in simulation. This equation will include both VOT and VOR for the segments identified.