“They can’t put down the phone, or they can’t not look at it,” said Dr. David Strayer, a distracted-driving researcher. “And in the context of trying to drive — it’s just a really dangerous combination.”

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Eyes off the road, head down texting, vehicle swerving — no one wants to be that driver.

Research has shown that taking eyes off the road for a few seconds or multitasking are as dangerous as driving drunk. Officials say it causes thousands of fatal motor-vehicle crashes annually. Lawmakers over years have responded to the issue with sweeping policy changes across the country, including Washington, where lawmakers are considering proposals to toughen the state’s distracted-driving laws.

So, why do drivers still impulsively reach for their phones?

According to Dr. David Strayer, a cognitive psychologist at the University of Utah whose research on distracted driving has informed people globally, the answer is simple: dopaminergic neurotransmitters. (Or, for nonscientists, chemicals in the brain that signal other parts of the brain to act.)

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“When the phone goes off, people feel compelled to look at that phone. They feel compelled because it’s actually a part of their social network that’s reaching out to them,” he said. “It’s triggering some of the dopaminergic neurotransmitter systems that are associated with reward.”

Dr. Barbara Jennings, of Sandia National Laboratories, summed up the brain’s natural chemical response to cellphones in a 2013 TED Talk as this:

“Dopamine is the chemical that’s responsible for our seeking,” she said. “So, we look for something and we find it, and we get a dopamine release. And we look for something else, and we get another dopamine release.”

In other words, dopamine is a neurotransmitter that sends signals in the brain that a reward was received, whether felt through pleasure or motivation, and it helps promote remembering that activity. The same chemical cycle comes from activities such as gambling, sex and some drug use that increase dopamine levels.

So, while behind the wheel, people with more addictive behavior patterns have a stronger urge to pick up devices for notifications or calls, Strayer said.

“They can’t put down the phone, or they can’t not look at it,” Strayer said. “And in the context of trying to drive — it’s just a really dangerous combination.”

Physiology 101: The front part of the brain is called the prefrontal cortex. It’s responsible for multitasking, decision making and planning.

So, when drivers interact with phones or other electronics, while they’re also making decisions on the road, they’re exercising the same part of the brain.

“Our brain is overloaded, that’s really what happens,” Strayer said. “You’re trying to do two separate things at the same time, and there are issues.”

Imaging studies that show high levels of blood flowing through the brain when people try to multitask have proved this, he said.

The odds of crashing increase sharply after drivers take their eyes off the road for four seconds, the time it takes to read an average text message, Strayer said. Changing the radio or climate control with a button takes between one and two seconds.

Programming a GPS while driving can take up to four to six minutes, Strayer said.

And the distractions don’t have to be physical.

Cognitive distractions are a significant source of crashes, he said. Using voice commands to change music or compose a voice text, for instance, can take more than 15 seconds, according to Strayer.

Most voice-based interactions in new vehicles exceed safe levels of interaction time, he said.

“It might seem like a good alternative to keep eyes on the road, but you’re engaging the same parts of the brain,” he said. “Short interactions are safer than long interactions.”

In Washington, the current, decade-old laws prohibit drivers from using cellphones at their ears or to text.

Lawmakers now are mulling proposals that would ban all use of handheld devices in most situations, increase the fine on the second citation and prohibit watching video.

The Senate’s version of the legislation would also allow law-enforcement officers to penalize drivers for any type of distracted-driving activity, if officers pulled them over for a separate violation. Both the Senate and House bills are heading to rules committees where legislators will decide if they should move forward.

A Washington Traffic Safety Commission study released in January — the first of its kind — analyzed drivers’ behaviors at high-traffic intersections across the state and found roughly 9 percent of people drove distracted, the majority of whom were using phones.

Drivers are more likely to engage in distracting activities when they are waiting for a cue from a traffic signal, as well as when they are stopped at intersections, the study says.

Strayer began researching distracted driving at the turn of the millennium. And since then, besides the emergence of smartphones, the evolution of vehicles’ built-in electronic interfaces and other new features have shaped how he studies distracted driving.

“The car itself now becomes an extension of the phone,” he said.

Those sorts of technological changes, safety officials and researchers say, have played a part in the nation’s growing number of motor-vehicle deaths.

Last week, the National Safety Council released new numbers showing crash fatalities last year overall increased 6 percent nationwide.

“We’re seeing an unprecedented spike in fatal crashes,” Strayer said. “In all honesty, Facebook, liking things on Facebook, doing Twitter, Snapchat and Instagram — those things don’t belong with a driver when they’re driving.”