In Baltimore, they call it a “rough ride.” In Philadelphia, they had another name for it that hints at the age of the practice — a “nickel ride,” a reference to old-time amusement park rides that cost five cents. Other cities called them joy rides.

The slang terms mask a dark tradition of police misconduct in which suspects, seated or lying face down and in handcuffs in the back of a police wagon, are jolted and battered by an intentionally rough and bumpy ride that can do as much damage as a police baton without an officer having to administer a blow.

The exact cause of the spinal injury that Freddie Gray, 25, sustained while in police custody in Baltimore before his death April 19 has not been made clear. The police have said that he was not strapped into a seatbelt, a violation of department policy. That has led some to wonder whether he was deliberately left unbuckled, reminiscent of a practice that while little known has left a brutal, costly legacy of severe injuries and multimillion-dollar settlements throughout the country.