(CNN) For the first time in a decade, more than 40,000 people died on US roadways last year, according to estimates reported by the National Safety Council .

Overall, highway deaths increased 6% over 2015 and 14% over 2014. This is the sharpest two-year rise since 1964, says the council, a nonprofit focused on eliminating preventable deaths.

The worst month in 2016 was October, which contributed 3,790 to the total 40,200 highway deaths, according to the report. January saw the lowest number, with 2,740 deaths.

As might be expected due to the overall population of certain individual states, Texas, California and Florida each had more than 3,000 deaths in 2016.

Alaska, Vermont, Rhode Island and the District of Columbia had the least, with fewer than 100 deaths each.

Overall, the researchers estimated 12.4 deaths per 100,000 people in 2016, a 5% increase over the 2015 rate. They also estimate about 4.6 million motor-vehicle injuries required a medical consultation in 2016, an increase of 7% from 2015.

Figures from 2014 and 2015 were gathered from the National Center for Health Statistics, but estimates for 2016 are still considered a preliminary tally, compiled by the safety council from each state's traffic authorities.

More drivers on the road

"During the recession, the number of deaths on our roadways went down a lot. We were driving less," said Ken Kolosh, manager of statistics at the National Safety Council. Traffic deaths dropped during the years 2008 through 2010 , with a very slow increase then taking place until 2015

These days, gas prices are lower and job growth is better, so people are traveling more often. For 2016, the council estimated a 3% increase in motor-vehicle mileage over the previous year, however, this increase in traffic, unfortunately, also leads to a swelling number of highway fatalities.

However, a 3% increase in miles driven versus a 6% increase in deaths suggests something else is at play.

Kolosh saw evidence that "teenagers and young drivers were impacted and lost access to vehicles during the recession." With the economy improving, teens are back on the highways, he said.

"We see actually a decrease in drivers talking on their phones -- either handheld or hands-free -- but increasingly, we're seeing drivers texting or doing other activities on their phones," Kolosh said. Not surprisingly, he points to "our younger drivers, the 15- to 24-year-olds" as most responsible for this shift.

"At any given daylight moment, nearly 5% of them are likely texting or doing something else on their phones while behind the wheel," he said. "We're also seeing a very, very large increase in the number of vulnerable road users who are dying on our roads."

Vulnerable road users include pedestrians, bicyclists and motorcyclists.

Though it's known that distracted driving is on the rise, "the role of the distracted pedestrian" may be an understudied problem, according to Kolosh, who cites a 9% increase in the number of pedestrian deaths on the road between 2015 and 2016.

"We are pretty sure there's more distracted pedestrians in our towns, on our sidewalks, than ever before, and that's probably increasing," he said. Although aware that it's not safe to text while driving, pedestrians think nothing of doing so while walking, said Kolosh.

'Booze, belts and speed'

According to Kara Macek, senior director of communications and programs at the Governors Highway Safety Association, road death numbers "often fluctuate a bit year-to-year." However, "this is definitely a troubling new trend, and it's difficult to pinpoint one precise cause."

The association is a nonprofit representing state and territorial highway safety offices. Macek was not involved in the new safety report.

Macek also points to the growing economy, which has resulted in more people driving more often. She further attributes the increasing deaths to a rise in "our growing appetite for connectivity, which leads drivers to dangerous distractions," but believes the core reasons have not changed that much.

"What's killing people on the road? It's still booze, belts and speed," said Macek, who noted that in 2015, alcohol and speed were factors in 28% and 27% of fatalities, while 48% of those killed in car crashes were not buckled up.

Jessica Cicchino, vice president of research at the Insurance Institute for Highway Safety, an independent scientific and educational organization, also believes economic recovery is the main factor behind the recent increase in deaths.

"It's not just that Americans drive more miles when the economy improves. It's the kind of miles they drive," said Cicchino, who did not contribute to the new report. "What comes back after a recession is the optional driving that's riskier, like going out on the weekends or taking long trips on unfamiliar roads."

Because she didn't see "a spike in cell phone use cited as a factor in fatal crashes," Cicchino is less likely to blame distracted driving. However, she said, "teens, the age group with the highest fatal crash rates per mile driven, are back on the road after the recession."

In addition, many states may be implementing policies that counter highway safety, according to Cicchino.

"In the last three years alone, 13 states have raised speed limits on at least some portion of their interstates," she said: Idaho, Illinois, Maryland, Michigan, Montana, Nevada, New Hampshire, Oregon, South Dakota, Utah, Washington, Wisconsin and Wyoming.

Of these states, five states -- Maryland, Montana, South Dakota, Washington and Wyoming -- showed a diminished number of highway deaths, however the majority showed increases, suggesting her theory is mainly correct.

Of all the states, Wyoming had the most improved rate, with a 25% decrease in roadway fatalities over the past two years, from 149 deaths in 2014 to 112 in 2016.

Wyoming, the model state

Lt. David Wagener of the Wyoming Highway Patrol finds it difficult to pinpoint the reason why his state is leading the nation in decreased highway fatalities.

"There was some slowdown in coal and other natural resource industries in Wyoming in 2016, so there were less people on the highways because of that, and there was less traffic moving, so that's one reason," he said.

"But really," he said, "it comes down to the individual making good decisions before they get behind the wheel and good decisions when they are driving."

Those good decisions include "making sure they get enough sleep, making sure they're not driving impaired, making sure they're wearing seat belts, making sure children in the vehicle are buckled in or wearing child restraints."

His unofficial numbers match up with the estimates from the Safety Council.

"According to the spreadsheet I have, 55 of those 112 fatalities had a seat belt available in the vehicle they were in, yet they chose not to wear it at the time of the crash," Wagener said.

"We have 34 listed as alcohol-related," he added. Wyoming also counted 24 deaths among motorcyclists -- 39 rollover-related, nine weather-related -- and three deaths among ATV drivers.

" Highway Patrol Sgt. Dwayne Ellis credits the Alive at 25 " program for significantly reducing the number of crashes and deaths in his state.

"We've taught well over 6,000 kids since the (program's) inception in late 2008, and of those, we've been able to identify only six who have died in a crash either as a driver or passenger before their 25th birthday," said Ellis, who is the state's safety education coordinator.

Though he was not able to provide numbers from 2007 to show the difference, he knows the program is extremely successful in part through feedback from both parents and young adults.

"What it does is, it talks about choice-making and consequences and how the choices that they make while driving not only affect them but affect everyone around them and everybody they know," Ellis said. "We empower them to think about the consequences and make good choices and let them know they are in control of their life -- it's whether they want to take control."

The class, part of a national program, is given in schools as part of the drivers education curriculum or can be taken on a volunteer basis or as an insurance deduction. Some people who have received a citation for speeding may be required by the court to take the class.

Wyoming starts them young, beginning with safety lessons in kindergarten via the "Little Convincer." This stationary platform used in presentations demonstrates how teddy bears not buckled into their seats will fall out during a crash. Then, the kids themselves can buckle themselves into the seat.

The adult version of the "convincer" uses a rollover machine and unrestrained dummies who are ejected, flying through the air, when they're not properly buckled into place.

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Back on the national level, Kolosh believes the US is still doing better overall than in the past.

"The number of deaths on our roadways really peaked in the 1970s," he said. Back then, "a lot of the safety advances that we've all become quite accustomed to" had not yet taken place," he noted.

At that time, the US did not have strong DUI laws or a lot of safety advances (such as airbags) in vehicles. The nation also did not have graduated programs to ease teenagers into becoming full-fledged licensed drivers.

"Our roads are much safer than they were in the '70s," Kolosh said.