NAFTA rules allow trucks to deliver goods from Mexico or an international port to a specific U.S. location, then return to Mexico
One study predicted that Mexican trucks can add 50 tons per day of smog-forming emissions -- more than pollution generated by the region's 350 biggest industrial sources combined. Southern California air quality regulators warned that smog could get worse because of a sharp increase in the number of polluting diesel engines on the freeways.
About 12 percent of Mexican trucks fail the tailpipe visibility test, compared with 6 percent of California trucks
This makes it that much more difficult for California communities to meet federally mandated air quality standards. e.g mor taxes for the legal residents.
More taxes, more traffic conjestion and more smog......
http://www.dailynews.com/Stories/0,1413,200~20954~2237167,00.html
It ain't hardly about tailpipe visibility tests.
Get a good night's rest. I'm about to.