Texas’s top environmental officials approved a major new plan yesterday for cleaning up the air of Houston, the country’s smoggiest city. The plan by the Texas Natural Resource Conservation Commission, which would bring the area into compliance with federal clean air standards by 2007, would cap the speed limit in an eight-country region at 55 miles per hour, require stricter tailpipe tests for vehicles, and ban the use of diesel construction equipment during morning hours for part of the year. The U.S. EPA is expected to approve the plan (especially if Texas Gov. George Bush becomes president). Some environmentalists criticized the plan for not including aggressive enough measures to fight ozone pollution.