Appendix A Transport modelling process
The following is provided as a guide to assist in defining and implementing the transport modelling process.
Consolidate the transport modelling task
This step involves discussing the transport modelling requirements to determine the scale and scope of the transport modelling.
- Review the purpose, goals and objectives of the task or study
- Review the timeline for the task or study
- Identify how transport modelling can contribute to informing the study goals and objectives within the specified timeline
- Identify and confirm the scale and scope of transport modelling required:
- strategic level
- regional level
- corridor level
- Confirm the time period to be modelled:
- peak (am, inter-peak and pm)
- Confirm the transport network and land use options to be modelled. These options need to be defined early in the process to determine the resources required to undertake the modelling
- Confirm the calibration and validation criteria for the modelling task:
- root mean square error (RMSE)
- travel time reporting
- Confirm the timelines for the modelling task
- Confirm the outputs from the modelling task. Examples of transport modelling outputs are:
- highway link volumes
- public transport patronage
- transport network performance indicators e.g. vehicle-hours, vehicle-distance, passenger-kilometres, levels of congestion, average speeds and travel times.
Identify and source the data required for the transport modelling task:
- Revealed preference data
- Traffic counts (mid-block, intersection)
- Route (link) travel times
- Demographic (population, employment)
- Land use (quantum of industrial, residential, commercial land)
- Stated preference data
- Public transport boarding and alighting data.
Model calibration and validation
Undertake the Reference (Base) Case transport model calibration and validation according to the criteria presented in Appendix C.
Forecasts are used to determine the performance of alternative scenarios of future land use and transportation systems. Options development would normally include different land use and transport systems and mixtures of highway and transit services and facilities. Since land use affects travel and travel affects land use, both must be considered.
Undertake the modelling of the various options and produce the demand and assignment outputs and network performance indicators such as:
- Mode shares
- Total vehicle-kilometres, vehicle-hours of travel and passenger kilometres travelled
- Total network travel time
- Vehicle operating and travel time costs
- Emissions – CO2, CO, NOx, CH4, HC, PM10, PM2.5.
- The modelled options should be compared to the calibrated and validated Base Case model on the basis of:
- traffic volumes
- public transport patronages
- network performance indicators.
Sensitivity analysis is usually undertaken to assess the response of the forecasts to a range of assumptions around an agreed transport network and demand scenario, usually the ‘Do-Minimum’ Case. The sensitivity testing may include:
- An allowance for generated / induced travel
- Ranges of growth in travel demand
- Changes in model parameter values
- Public transport fare changes
- Different planning or economic growth assumptions
- An assessment of complementary schemes such as travel behaviour change initiatives.
Economic appraisal is undertaken to assess the economic benefits of preferred options. Transport user benefits are derived by comparing the effects of the scheme against a ‘Do-Minimum’ Case, discounted over the assumed life of the scheme, and compared with scheme cost estimates and revenue implications.
A Modelling Report demonstrates that the transport model appropriately reproduces an existing situation and summarises the accuracy of the base from which the forecasts are produced.
The Modelling Report should also include the aims and objectives of the modelling task, document the assignment validation and output, document the details of any model calibration and report on the economic appraisal.
The Modelling Report should include:
- A description of the modelling task, aims and objectives
- A description of the data used in calibrating and validating the model
- The model calibration outcome
- Documentation of the modelling assumptions
- Documentation of the model validation
- Documentation of the economic appraisal.