One of the major sources of savings is simply the lower costs of financing through public procurement and financing--i.e., not P3s. Over the 30 or 40 years that these might be amortized those 100 or 200 basis points can be a really substantial amount. Unfortunately, a lot of the value-for-money studies that are done by provincial governments really obfuscate the information. They present just a few pages of information. It's really not transparent. Unfortunately, that lack of transparency about the costing is endemic to P3 projects as well, because the public just does not have access to that information, which is often protected by commercial confidentiality and thousands of pages of legal contracts.
On October 17th, 2011. See this statement in context.