The Transportation Department issued a regulation Friday requiring states to set minimum standards for both written and road tests in the licensing of commercial drivers.

Under the regulation, which takes effect immediately, commercial drivers will be required to pass a written test of no fewer than 30 questions, answering at least 80 percent of them correctly to get a state license.Drivers also will be required to demonstrate skill at driving the type of vehicle they intend to operate. States will be allowed to exempt some commercial drivers who already have licenses and a good driving record.