A Wednesday shootout on the streets of Washington Highlands left a cop injured and a carjacking suspect dead. But before the suspect expired, he went on an unusual ambulance ride that involved moving him from one vehicle to another on the shoulder of Interstate 295. While this might appear to be another story of Fire and Emergency Medical Services dysfunction, the story is rather more complicated. As WUSA-TV explains, newer-model diesel engines are required by federal regulations to have emission-control features that, in some circumstances, require the motor to shut down for “regeneration” — a process in which the exhaust system burns off trapped soot. The need for regeneration can be unpredictable , and there have been calls in recent years to exempt emergency response vehicles from the federal requirements. Deputy Chief John Donnelly told Channel 9, “We’re not in a position to fight the EPA regulations, and we’re not even going to try.” The transfer to a second ambulance delayed 34-year-old Nathaniel McRae’s arrival at a hospital by seven minutes; FEMS insists the wait did not play a role in his death.