“It’s kind of horrible,” Milhorn said, standing in her front yard, staring out onto the abandoned development next door, as a man on a motorcycle gunned his engine, speeding in noisy circles around the empty streets.

Milhorn and her husband erected a fence on their property’s boundary to keep out the animals, but that doesn’t stop the people who come in to cruise around the empty streets or party in the tall grass. A road block that had been erected to keep out trespassers was taken down after a drunk driver rammed into it in the dark. Now, the empty streets of the cul-de-sac have turned into a track for drag racers and bikers.

“One of them bit the dust in the middle of the night and was screaming out here in the dark,” Milhorn said, shaking her head.

There are hundreds of zombie subdivisions like this one scattered across the country. They're one of the most visible reminders of the housing boom and bust, planned and paved in the heady days where it seemed that everybody wanted a home in the suburbs, and could afford it, too. But when the economy tanked, many of the developers behind these subdivisions went belly-up, and construction stopped. In some cases, a few people have moved into homes in these half-built subdivisions, requiring services to be delivered there. In others, the land is empty, except for roads, sidewalks, and the few street signs that haven't been stolen yet. In some counties in the West, anywhere from 15 to 33 percent of all subdivision lots are vacant, according to the Sonoran Institute.

“Since the post-2007 real estate bust, which hit many parts of the region severely, eroding subdivision roads now slice through farmland and open space, and 'spec' houses stand alone amid many rural and suburban landscapes,” author Jim Holway wrote in a report by the Lincoln Institute of Land Policy about zombie subdivisions. “Without correction, they will continue to weaken fiscal health, property values and quality of life in affected communities.”

Empty lots can cause wildfires and flooding contamination, and can bring down the property values of nearby homes. They can also cost local governments money that they don't necessarily have, since the municipalities may have to provide public safety or snow removal to far-flung areas, without the benefit of the property taxes that had been expected.

It's unclear just how to 'fix' these zombie subdivisions. While some will be completed as the economy recovers, others may lie dormant for a long time. That’s especially true now that many young people and boomers want to live in walkable, urban environments, rather than subdivisions where they have to drive to everything.

But if roads have been paved or a developer has installed infrastructure improvements, it’s very hard to just revert the space back to farmland. Local governments who try to stop building—even if there is little demand—can be sued for preventing development where it had once been approved.