Despite President Bush's attempt to open U.S. highways to Mexican truckers, a federal appeals court in January temporarily barred the trucks, ruling that the administration was in violation of federal environmental laws. For the past ten years, Mexican trucks have been restricted to operating within a 20-mile commercial border zone. President Bush last year lifted the ban. Yet, in a 3-0 ruling, the U.S. 9th Circuit Court of Appeals said the administration's claim that opening the U.S. roadways would create only a minimal environmental impact was based on a "woefully inadequate" review of potential health hazards from the Mexican trucks, many of which do not meet U.S. air pollution standards. Further, the court said the U.S. Department of Transportation must conduct a detailed study of the possible environmental effects of the diesel burning trucks. It's expected that more studies on the potential environmental impact could take at least six months.