New York City will spend $1.8 million this year to roll out “mobile trauma units,” or buses filled with counselors and peacekeepers, to crime scenes throughout the city in an effort to ease tensions in communities after acts of violence.

The buses will be deployed in January 2019 to each borough to provide trauma relief, as well as job and educational opportunities. Some team members have prior criminal records and former gang affiliations. Known as “violence interrupters,” they use their credibility and connections to resolve...