Every time governments contemplate massive investments in urban road infrastructure, it's instructive to bear in mind there's a much better alternative. Instead of building something gargantuan like a road tunnel, they could instead elect to implement congestion charging across the metropolitan area.

This involves charging motorists for the use of road space. Ideally, the charge will vary with demand, rising to whatever level is necessary to keep traffic flowing at some minimum speed (which would in most cases still be well below the maximum permitted).