Montgomery County police Sgt. Mark White pulls over 42-year-old Angela Matsen of Rockville, who was talking on her phone while driving. (Sarah L. Voisin/The Washington Post)

Angie Matsen was humming down the road toward Rockville on a perfect October afternoon, but her thoughts were about 1,800 miles away in Wyoming, and there was one other notable thing about her driving.

“I got one with her phone to her ear. Going after her,” Montgomery County police Sgt. Mark White radioed as he weaved through traffic and then flicked on his flashing red and blue lights to pull over Matsen’s charcoal gray Toyota SUV.

A few seconds later, he was leaning toward her open window to say she’d broken an old law that suddenly has a new bite. It has been illegal for drivers to use a handheld cellphone in Maryland for three years, but since Tuesday, the law has become a lot easier to enforce.

Police no longer are required to find some other reason to pull a driver over to ticket them for illegal cellphone use.

And that’s just what White and a squad of Montgomery police officers spent time doing last week: watching for drivers with a phone pressed to their ear. In all of last year, Montgomery police wrote 533 tickets for illegal cellphone use. At the rate they were handing them out, they will top last year’s total by Halloween.

“Distracted driving is an overwhelming issue,” White said. “I can drive up and down the road and observe people talking on their phones, fixing their hair, and I saw somebody reading a book the other day.”

Nationwide, distracted driving was to blame for 3,331 roadway fatalities, 387,000 injuries and 10 percent of all crashes in 2011, according to federal statistics. The percentage gets higher for drivers 19 or younger, with 21 percent who were involved in fatal accidents said to have been distracted by their cellphones.

Because those numbers come from the credible National Highway Traffic Safety Administration, they get a deserved amount of attention, but closer to the ground, police know they are squishy.

“It’s been an under-reported crime, because it’s only the few who admit to it,” said Capt. Tom Didone, head of Montgomery’s traffic division and White’s boss.

For something that has become a fixture in everyday life, the cellphone has been around for about a nanosecond, and research on the distraction it creates behind the wheel for even less time. But some studies suggest that bans on handheld use — the District and 11 states in addition to Maryland have them — won’t lower the number of distracted-driving ­crashes.

They support a simple notion that, despite all the bravado about multitasking, there are limits on how much business the brain can effectively conduct at any given time.

David Rock, author of “Your Brain at Work,” likens the brain to a theater stage that has room for only a certain number of actors.

Deciding whether the traffic light is about to change, whether the next turn is the correct one and whether the driver to the right is about to change lanes, while talking to someone about a subject unrelated to driving, crowds the stage and compromises the ability to focus well on any one of those things.

Most drivers know that, but it’s been estimated that an average of 660,000 Americans are using electronic devices while driving at any given moment during daylight hours. Various surveys have shown that drivers feel comfortable using their phones but wish other people wouldn’t.

In a Washington Post poll conducted in June, 65 percent of people who live in the D.C. region said they very often see other people with a cellphone to their ear. Only 14 percent admitted to doing that very often themselves.

The National Transportation Safety Board has called for a total ban on cellphone use while driving.

Matsen readily admitted that she was on the phone when White pulled her over. She had just moved from Wyoming in August and said she’d been too busy getting three children settled in school to pay much attention to the news. Are people distracted by their phones?

“Yes and no,” she said, pausing for a second.

“Yes, you are distracted. I was talking to my best friend in Wyoming about another friend who was hit [by a vehicle] while he was running. He’s in critical condition.”

She got off with a warning. Others were not so lucky, as White and his squad used an unmarked SUV and three patrol cars to chase down cellphone users on Route 355 between Gaithersburg and Rockville.

White stationed his SUV at the beginning of a left-turn lane near the Shady Grove Metro station and radioed the trio of officers — Jeremy Smalley, Rob Jacarouso and Jeff Innocenti — who parked just out of sight down the road.

“Gold Honda, she’s got it directly up to her nose, talking,” he radioed, and then a few minutes later: “Dodge Durango, has the phone up to her ear.”

They said they hadn’t had to listen to a lot of bellyaching as they gave out a dozen tickets during the first day of enforcement.

“A couple of people said, ‘Oh, yeah, the law went into effect.’ . . . They knew about it,” Smalley said.

On day two, it was a different story.

“She said she was just looking at it,” Jacarouso radioed after one stop.

“Oh, yeah?” White shot back. “Unless it’s a scent phone, she was talking. She had it right up against her nose.”

Later in the afternoon, Innocenti saw a woman pass by in a red Ford pickup with her phone in hand. After he ticketed her — it’s $83 for the first offense, $140 for the second, $160 for the third — he returned to the cruiser shaking his head.

“She said, ‘Speakerphone is hands-free, isn’t it?’ ” he said. “I said, ‘Well, not if you’re holding it in your hand.’ ”

One study equated distracted driving with drunken driving, a comparison with which Innocenti agrees.

“A lot of the time, you’ll see a car driving like they’re DUI, but you get up to them and they’re on their phone,” he said. “And do they cause accidents? Oh, yeah.”