It’s been said that if you build it, they will come.

But what if they’ve already arrived — and then you don’t build it after all?

That’s the situation facing suburbs along the proposed Southwest Light Rail Transit line as legislators continue their long battle over the line’s state funding.

The line has been touted by its backers as a spur to future development in the west-metro suburbs. In reality, development has already occurred — quite a bit of it.

For at least a decade, and in some cases longer, city officials and planners have guided development with the Southwest line in mind.

Thousands of apartment units have been built or are underway along the line’s route, with more in planning. Hundreds of millions of dollars have been invested in commercial development, all with the expectation that the trains would be coming.

So what happens if they don’t?

“I think it will be a staggering setback for these communities,” said Peter McLaughlin, a Hennepin County commissioner and one of the Southwest line’s most vigorous supporters. “The essential element, their connectivity to the 21st-century economy, will be destroyed.”