Edinburgh Napier University

  The thesis reports the outcome of three main investigations. The first investigated the technical issues involved in how commuter’s departure time and mode choice might be affected by road user charging. The second investigated the public’s preferences for allocating revenues from a road user charging scheme. Both were based on surveys in Edinburgh, where plans for a particular scheme had been developed1. The third assessed how different charging levels affected both the demand for travel by car and the revenue generated, raising questions as to how the balance between differing objectives might be struck.

The surveys undertaken used stated preference techniques to investigate departure time and mode choice changes for a sample of 211 employees working in the city centre of Edinburgh in June 2002.

Departure time to work was found to be influenced not only by the work schedule (hitherto the only component of scheduling flexibility) but also by other social factors. These included whether or not regular activities were carried out before or on the way to work; and whether or not a respondent had dependent children where all adults in the household were working. The highest levels of scheduling flexibility7 were observed for individuals who had flexibility in both their work schedules and non-work activities. The calibrated models support the relevance of aspects of flexibility to the departure time choice. Mode choice was modelled using data from stated preference experiments. It was shown that many car drivers were prepared to switch to the bus when faced with paying a toll. Moreover, a small percentage of bus users were prepared to switch from the bus to the car, perhaps seeing an opportunistic reduction in traffic levels, which would make the car a viable alternative.

Respondent’s preferences for the allocation of revenues from a road user charging scheme were jointly modelled with choice of mode of travel using the nested logit model. The justification for this is that the allocation of the revenues might affect other choice decisions. The overall goodness of fit of the model was reasonable, although not all of the model coefficients were statistically significant. However, the approach to jointly modelling mode choice and revenue allocation offers an interesting concept, which is worthy of further research.

The effect of different levels of charge on traffic levels and revenue raised was investigated based on the three levels of charge, which were offered to all respondents. The findings suggest that there would be a slight increase in traffic at the lowest level of charge (in this case £2), while traffic reduces significantly at each of the next two levels of charge (£3.50 and £5). On the other hand, the revenue from the scheme increases with increasing levels of charging (up to £3.50), and then decreases with the decrease in demand. Therefore, based on this pattern, alternative optimum levels of charge can be identified to achieve different objectives. For example, in this case, if the objective is to maximise revenues, then the optimum level of charging appears to be about £3.50 — somewhat above the level of charge of £2 proposed in the Edinburgh scheme. If the objective is to reduce traffic levels, that would certainly require a higher charge than £2, but what the optimum level of charging might be cannot be determined for such an objective, since the quantity demanded still appears to be falling even when the charge is £5.

The main principle behind the theory of road user charging is that motorists should be charged for using the roads, where the extent of the charge reflects the costs that they impose on others and on the environment (thus helping to reduce traffic congestion). However, the experience from other studies suggests that in almost all cases the revenues generated are as relevant. These two objectives are conflicting; there is a need for further research and development of methodologies for the investigation of optimum specifications of schemes that reach a satisfactory compromise between the two objectives, taking into account the fact that raising revenue helps to provide funds that (under a hypothecated scheme) can be ploughed back into transport, and hence help reduce the demand for road use. Moreover, there is a need for an explicit recognition of the relevance of the revenues for the success of the scheme in terms of technicality and public acceptability.