Where and how much to invest in bicycle networks: Trip-based cost–benefit optimisation under uncertain uptake

Choosing where to invest in bicycle infrastructure requires an understanding of the benefits for existing and potential riders, as well as how different projects function together. We used a trip-based model to examine project selection and expenditure for Greater Melbourne’s Strategic Cycling Corridors. The model assesses safety benefits, mode shifts, economic benefits and emission reductions following road infrastructure improvements, and identifies the projects that maximise expected net present value (NPV) within a capital funding limit. Under Reference delivery costs, the model selected 41 projects with capital expenditure of $20.6 million, with expected NPV of $14.9 million and a benefit–cost ratio (BCR) of 1.62. To examine how costs affect investment, we repeated selection under lower and higher rates. Lower costs supported 101 upgrades and 35 new protected sections; reference costs supported 38 upgrades and three new sections; and Higher costs supported six upgrades but no new sections. To test whether accounting for lower uptake changes investment decisions, we tested the model giving greater importance to returns when fewer people change mode. This reduced reference-cost expenditure to $18.7 million while leaving expected NPV almost unchanged. To assess whether joint appraisal changes selection, we compared it with separate project appraisal. In the comparison with the largest gain, joint optimisation selected two additional projects and increased risk-adjusted net value by $0.10 million under Reference costs. Therefore, by demonstrating how delivery costs, route and safety assumptions influence the selected program, we showed the importance of assessing both investment scale and project priorities under uncertain assumptions.