11.5 - Travel impacts
- 11.1 - Evaluation of private sector financing and road tolling
- 11.2 - Method of evaluation
- 11.3 - Stages of analysis
- 11.4 - Do minimum
- 11.5 - Travel impacts
- 11.6 - Costs
- 11.7 - Benefits
- 11.8 - Period of analysis
- 11.9 - Financial evaluation
- 11.10 - Cost benefit evaluation
- 11.11 - Alternatives and options
- 11.12 - Sensitivity and risk analysis
- 11.13 - References
11.5 - Travel impacts
Introduction
The draft Transit NZ implementation guide for finance and toll projects (reference 1) provides guidance on the traffic/toll modelling requirements and methods for assessing toll route feasibility.
Traffic modelling
Traffic modelling for a tolled road (and the surrounding road network) is an essential input to evaluation. The main purpose of the assignment part of the traffic modelling is to forecast traffic volumes (and corresponding traffic speeds) on each part of the road network and particularly on the toll road. The toll road traffic volumes in turn determine toll revenues.
For accurate forecasting of route choice between the toll road and alternative routes, it is important to take into account the full range of behavioural preferences of potential users of the toll road. This generally requires more sophisticated choice models and a better understanding of motorists preferences than is the cases in standard traffic models.
Traffic modelling used for road tolling projects should take into account behavioural responses such as:
- peak spreading/contraction
- trip end redistribution
- modal shift
- trip generation/suppression.
The split of traffic between the toll road and alternative routes is likely to be sensitive to the level of congestion on the road network and the mix of trip purposes by time of day/day of week. Therefore, detailed traffic modelling must separately consider periods with differing levels of congestion. Expansion or annualisation factors need to be applied separately to the results for each of these periods based on the characteristics of the toll route traffic rather than the traffic volumes in general.
