The Twin Cities of Minneapolis and St. Paul have been an epicenter of the U.S. stadium-and-arena boom, rolling out five major sports facilities since 1990 that together cost more than $2 billion.

Now, the neighboring cities are readying for a sixth: a 20,000-seat, $150 million Major League Soccer stadium to be built by 2018 in St. Paul about halfway between the two downtowns.

The St. Paul City Council earlier this month approved $18 million in spending on infrastructure for the stadium, which is meant to spur neighboring real-estate development. The stadium, which is otherwise to be constructed with private dollars, also would be exempt from property taxes.

…The Twin Cities have been particularly zealous. Locals attribute that in part to the unusual political dynamics of having two cities adjacent to one another—with their downtowns just 12 miles apart—and a layering of other different governmental bodies that have given public aid.