2010 Toyota Prius ad comparing its emissions to those of a sheep
(cropped)Enlarge Photo Some of the first emissions regulations
in the world came about because of the way the Los Angeles Basin
is shaped. Reports of smog in southern California started with
the Conquistadors, and by the Sixties, LA was notorious for its
foul air. California began regulating auto emissions before the
U.S. Environmental Protection Agency even existed, and motor
vehicles have been a focus of emissions laws ever since. So-
called criteria pollutants (carbon monoxide, hydrocarbons, and
nitrous oxides) have been reduced by more than 90 percent since
1970. Vehicle emissions of greenhouse gases, primarily carbon
dioxide (CO2), are inversely proportional to gas mileage: The
higher the mileage, the lower the CO2 output. 2010 Toyota Prius
ad comparing its emissions to those of a sheepEnlarge Photo With
fuel economy levels set to rise to 34 mpg by 2016, and total
U.S. vehicle miles traveled flat or increasing just slightly,
many environment