LA Times: At a laboratory in downtown Los Angeles, a big rig spins its wheels on massive rollers as a metal tube funnels its exhaust into an array of air quality sensors. Engineers track the roaring truck's emissions from a bank of computer screens.
The brand-new diesel truck is among the cleanest on the road, the engineers at the California Air Resources Board testing lab say. Even so, its 550-horsepower engine spews out more than 20 times the smog-forming nitrogen oxides of a typical gasoline-powered...