Trigger warning (especially for the articles linked here)
In 2005, a powerful lobbyist in Miami Beach named Ron Book (after discovering that his young daughter was the survivor of sexual assault) helped to pass local residency restrictions on child sex offenders found guilty in a court of law. These restrictions barred child sex offenders from living within 2500 feet of any place where children gathered: schools, daycare centers, or playgrounds. These restrictions meant that entire cities became off limits for these perpetrators to live after being released from prison. While probation restrictions may differ, many of them face only a curfew and living restrictions within this curfew, but are free to work or spend their days without spacial restrictions.
What ended up happening due to this ordinance and others around the region, is that sex offenders were released homeless, and told that one of the only places that they could live was under the Julia Tuttle causeway, a homeless colony of child sex offenders living under a bridge of the highway. This has caused major problems for the government of the region, as they try to deal with a very specific homeless population. The DMV even started issuing drivers licenses with the address listed as "under the Julia Tuttle causeway bridge". Other regions around the country have found themselves with similar colonies, prompting people to doubt the effectiveness and safety of the original ordinances meant to create a safer space for their children. By destabilizing the sex offenders, experts on sexual crimes were saying that it could create a much less safe environment for children.
For more information, you can read an article from Newsweek from last July about the situation in Miami (warning, very detailed and very triggering). Embedded in the article is also a short video clip about life under the bridge. And you can also listen to a story from this week's The American Life episode - theme Bridges - which looks at the more recent developments and is much less about the offenses of perpetrators and more about the legal and political ramifications of the policies