THE NUMBER of Americans killed in traffic accidents has plummeted in the past couple of decades, thanks to safer cars, wider use of seat belts, public awareness campaigns, better laws and enforcement and, most recently, reduced mileage among younger drivers, a byproduct of the recession. Among the most encouraging trends has been a dramatic drop in alcohol-related traffic deaths, which account for about 30 percent of all road fatalities today, down from 60 percent 30 years ago, when drunken driving was almost a cultural norm.

Now state legislatures around the country are taking tough steps to make life even more difficult for those who would drink and drive. Key among the new measures are laws requiring the installation of in-car breathalyzers for all motorists convicted of drunken driving. The devices, known as ignition interlocks, prevent engines from starting if a driver’s blood-alcohol level registers above a preset level.

Fifteen states plus a chunk of California have enacted such legislation, which has cut down on repeat offenses. Now a similar measure is hanging in the balance in Virginia, where it has reached the floor of the state Senate for the first time after five straight years of dying in committee. The bill has cleared the House of Delegates and is backed by Gov. Robert F. McDonnell (R). Its enactment would save lives.

Around the country, ignition interlocks have reduced highway deaths when they are mandatory for offenders who drove with a blood-alcohol content (BAC) of .08 or more. They have been less effective in states like Virginia, where they are required only for offenders convicted with BACs nearly twice as high — a level at which most people could hardly stand, let alone drive. The legislation now before the state Senate would set the bar in Virginia at the tougher .08 level for all drivers.

Opponents, including Senate Majority Leader Thomas K. Norment Jr. (R-James City), argue that’s too onerous a standard for first-time offenders and others who might be “one sip over the line” and that the bill would remove a judge’s discretion in sentencing. Some also note the price burden of the device, which would cost a convicted motorist about $400 for the six months it would be required.

Those fair concerns are easily outweighed by the carnage that would be avoided on Virginia’s roads. Studies have shown that many drivers responsible for alcohol-related traffic deaths had blood-alcohol levels below .15. In other words, the commonwealth’s standard is simply inadequate.

Virginia has been a laggard on traffic safety laws. It has been slow to join other states that have stiffened legislation on seat belts; cellphone use by teenage drivers; text messaging; and open containers. According to a new report by Advocates for Highway and Auto Safety, an advocacy group, Virginia is among just eight states with a “dangerous lack of basic laws” regarding highway safety. It’s time for the state to quit its membership in that club.