NHTSA reports sharp spike in traffic deaths

It's expected to be the busiest Thanksgiving holiday on the roads since 2007.

"Our GPS all of a sudden added another hour on to our travel time so that was super unexpected," said Erin Misar, on the road from Rochester, New York to Durham, North Carolina.

Just as 42 million Americans hit the road, the National Highway Traffic Safety Administration reported a sharp spike in traffic deaths for the first half of 2015.

More than 16,000 people died, up more than eight percent over the last year. If the trend holds for the year, that would be the sharpest percentage increase since 1946.

The biggest reason: almost half of those killed in passenger vehicles were not wearing their seat belts. Back seat passengers are a particular concern as they are less likely to buckle up, and 22 states do not require it. But back seat riders are still very much at risk in a crash.

Dr. Jim Hedlund studied back seat passenger behavior. "It takes a second, you don't have to think about, it doesn't cost you anything," Hedlund said of wearing a seat belt. "It is cheap, easy, and it may save your life."

Plummeting gas prices, the lowest on Thanksgiving since 2008, may also be a factor in the rise in traffic deaths says AAA's Tom Calcagni.

"Lower gas prices, more people are driving longer distances or more miles, the more people on the road, the more people driving long distances, the greater the risk."