We estimate net benefits arising from extensions to Auckland's Northern Motorway since 1991. Population, employment and land values rose substantially near the new exits and to the north of the motorway extension, relative to developments elsewhere.
We use changes in land values (controlling for other factors) to measure gross benefits of the extensions, which we compare with project costs to determine the project's benefit: cost ratio (B:C). The B:C is at least 6.3. We discuss the types of net benefit and cost that are included and excluded from these estimates, and contrast our methodology with traditional ex-ante B:C approaches.