The MVA, which held a news conference Wednesday to publicize the new law, said participation has increased from 5,500 in November 2008 to an estimated 9,100 today. The agency said the numbers have grown as more judges have become convinced of the effectiveness of the program.

Under the new law, certain drivers must agree to participate in the interlock program or face license suspension or revocation. They include drivers under 21 who violate alcohol restrictions, motorists with second drunk driving convictions within five years and people whose blood-alcohol tests register 0.15 percent or more. Under Maryland law, drivers who blow .07 can be found guilty of driving while impaired while those who registered .08 are considered intoxicated.

Maryland officials also claimed Wednesday that the state is the first in the nation to fully automate its ignition interlock program. The MVA said drivers in the program must report to one of the agency's five approved interlock vendors every 30 days to have their monitoring data downloaded and reported to program officials. It said violations are automatically flagged from the information sent to the providers.