Autism and early exposure to traffic pollution linked?

So where was all the autism from, say, 1940-1980 when U.S. air was not nearly as clean as it is today? In the 1950s and 1960s, Los Angeles air often hit ozone levels of 500 ppb — compare with today’s worst case levels of about 90 ppb. Pittsburgh-area air could contain more than 500+ micrograms of particulate matter per cubic meter 50% of the time — compare with today’s worst-case of maybe 40-50 micrograms per cubic meter. Ouch, it must hurt epidemiologists to think. [Los Angeles Times]