Kevin Campbell, Manager of Fleet Services at the City of Chicago’s Department of Fleet and Facility Management, aims to conserve across a network of more than 3,000 police vehicles, 500 garbage trucks, 300 salt-spreader trucks, 125 street sweepers and 100 ambulances — a total fleet of more than 12,000 vehicles. A handful of measures, from idling standards, to drastic nitrogen-oxide emissions reductions, keeps this massive fleet from heavily polluting Chicago’s air supply.