I don't think they're talking about PFI schemes ... more likely the plan is to get private sector investment without government money, which means we're looking at the new road projects becoming toll roads to generate income.
Assuming, of course, that there are any private sector investors that want to take part - it doesn't sound like the treasury have actually asked anyone whether they's like to invest! If they're not keen, government will likely have to underwrite the risk, which means the cost will end up on the balance sheet anyway, so we'll have the profits being sent offshore while the taxpayer underwrites the risk.
So this is really just an announcement that they hope some pension funds (or the Chinese) will want to open some toll roads in the UK, but they don't really know because they haven't asked them yet. Not much of a business plan is it?