PHILADELPHIA (CBS) — New research shows fixing up blighted properties and vacant lots reduces gun violence and the cost associated with it.

The study was conducted by the Perelman School of Medicine at the University of Pennsylvania. Doctor Charlie Branas, professor of Epidemiology and director of the Penn Urban Health Lab, says the research looked at 5,000 Philadelphia homes that had replaced plywood with windows, and installed new doors, plus greened up vacant lots.

“We found that gun violence was significantly reduced after these blighted properties had been repaired or greened. Significant reductions in gun violence, in some cases, over 30% for significant time, sometimes for years to come,” Branas said. “Once these spaces get improved, people don’t want them to revert to the way they were before so they’ll go the extra mile to make sure that there isn’t some sort of nuisance in the surrounding area.”

Branas says the cost of the fix compared to the cost of gun violence is immeasurable. He says the estimated cost of gun violence in the United States is $50-billion each year.

Branas says for each dollar spent on improving blighted homes and lots, the return on investment to taxpayers and society can be up to hundreds of dollars saved. That money would otherwise be spent on policing, medical costs and pain and suffering to victims and neighborhoods.

He says the Philadelphia model is now being considered by other cities like Flint, Michigan and New Orleans.