Appendix B Proposed steps in undertaking an ex-post CBA
BITRE’s ex-post CBAs are undertaken as follows:
- Provide a description of the project (design, cost, timing and history of the project)
- Locate and review ex-ante or initial CBA(s)
- Identify issues in ex-post evaluation (mostly emerging from the review of ex-ante CBAs)
- Replicate the ex-ante CBA
- Collect data for the ex-post CBA (for example, traffic and crash data)
- Update traffic and crash forecasts
- Undertake the ex-post CBA (including adjusting model inputs, updating model parameters and making other project-specific corrections)
- Compare results between ex-ante and ex-post CBAs
- Explain the difference
- Draw lessons.
An important consideration in undertaking an ex-post CBA is the potential timeframe associated with the process. This may be quite lengthy for larger scale initiatives and may not be cost effective for small scale initiatives.
For published examples applying the methodology, see BITRE (2007a and b).