Commentary As a general rule, if you see a shiny new transit megaproject approaching your town, you should get into a private automobile and drive slowly away. But Canadians should hit the gas hard, because even in a world where politicians and contractors manage to overestimate benefits and underestimate costs with uncanny precision, we are overachievers. A Dec. 26 Canadian Press story says a kilometre of urban subway worldwide in 2019 typically cost $300 million. What a bargain, you may exclaim, before considering that real subways are very big; London’s “Tube” has 400 km of track whereas New York’s has 399 and no nickname. And unfortunately, the story adds, in the Great White North it’s more like $700 million and rising. The story cites a study for the Residential and Civil Construction Alliance of Ontario, whose neutral name, appealing slogan “Constructing Ontario’s Future,” and emphasis on constructive, non-partisan collaboration makes …