As expected, the number of would-be drunken drivers stopped by ignition interlock devices has skyrocketed since Connecticut began implementing an expanded drunken driving law nearly two years ago.

From July 1, 2015, through May 31 this year, the devices stopped cars from starting 135,389 times, according to data the Connecticut chapter of Mothers Against Drunk Driving released Thursday.

That nearly two-year period swamped the four-year period from 2012 through most of 2015, when just more than 21,500 drivers couldn’t start their cars.

The reason for the surge? On July 1, 2015, Connecticut began requiring all convicted drunken drivers — including first-time offenders — to install the devices in their vehicles. Prior to that, only repeat offenders had to use them.

Before the new law, about 1,000 drivers had active interlock device requirements at any given time.

On June 5, that number was 7,533.

Johanna Krebs, program manager with MADD’s Connecticut office, said the numbers show the devices help reduce drunken driving and possibly save lives, too.

“It has stopped those potential drunk drivers from getting behind the wheel, which can cause crashes, fatalities, injuries — lives change forever," Krebs said. "That’s what we’re seeing.”

It works like this: Intoxicated drivers convicted for the first time first undergo a 45-day driver’s license suspension. They then must follow a series of steps — and pay a host of fees — to obtain and maintain an ignition interlock device, which prevents a car from starting if any alcohol is detected on a driver's breath. After six months, they’re free to go.

MADD avidly advocated for the legislation, which lawmakers passed in 2014. While members of the group weren’t thrilled at the time with the 45-day delay in linking drivers to the devices, they’re happy Connecticut’s on the progressive end when it comes to drunken driving.

“We know from a lot of the research that we do across the country that anywhere from 50 to 75 percent of people who have a suspended license will continue to drive anyway,” Krebs said. “After some time, asking, ‘Can you bring me here?’ starts to become not as easy, so they just continue to drive.”

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MADD’s release of the new numbers, which it procured from the state Department of Motor Vehicles, came just a couple of days before the start of another Independence Day weekend. That’s notable because the Fourth of July regularly ranks among the deadliest days for those on the roads. In the five-year span from 2011 through 2015, for example, the Insurance Institute for Highway Safety found there were 612 fatalities throughout the country on that day, or about 122 per year. That’s 45 more fatalities than New Year’s Day saw over the same period.

In 2015, data show, 36 percent of the traffic fatalities from the evening of July 2 through the morning of July 6 involved intoxicated drivers; 146 people died in those wrecks.

For the third year in a row, MADD Connecticut is partnering with Uber this holiday weekend to encourage people who are consuming alcohol not to drive. This time around, new Uber users, by using the code MADDCT, will get a free ride up to $20. For each of these signups, Uber in turn will donate $5 to MADD Connecticut.

Krebs said she knows the ignition interlock devices aren’t perfect. She has heard stories of the sensitive devices shutting off a car for the wrong reason. Sometimes mouthwash triggers them. Other times, it’s something a person ate. And she knows the intricacies of the devices vary across the eight vendors approved to provide them in Connecticut.

Despite the occasional misfires, Krebs pointed out, the devices allow people to continue relatively uninterrupted with their lives. Suspensions — if they’re followed — don’t.

“Is everything 100 percent?” Krebs asked. “No. But they are the best tools and technology we have available to us to use right now to prevent someone who’s been drinking from getting behind the wheel.”

“When we can see numbers like this,” she added, “we know the program is working and doing what it needs to do.”

l.boyle@theday.com