There has been a lot of discussion in the nation’s capital and in state capitals across the country lately about “infrastructure spending.” President Donald Trump made it a cornerstone of his presidential campaign, and he’s recently introduced his infrastructure spending plan.

However, before Congress can deliver on the president’s pledge to make America’s crumbling infrastructure great again, the administration and lawmakers must determine precisely what that term encompasses.

Everyone agrees that roads, bridges, tunnels and airports fall under this definition—there’s really no dispute there. But backers of other kinds of big-ticket projects covet a share of ...