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...