Schools are back in session, and a new tool can help parents gauge how safe the roads may be in their county and around schools their children attend.

An interactive map, produced by Zendrive, scores each state county and individual school district based on data that shows how frequently drivers use cells phones in school zones. 

Zendrive, a tech company that measures driver safety using phone sensors, developed the Zendrive School Safety Snapshot map, which takes into account factors like aggressive acceleration, hard braking and distracted phone use. 

Some 75,000 schools nationwide were mapped and analyzed, with over 3.4 billion driver miles driven within the districts.

The results showed that 1 in 3 drivers showed unsafe behavior in pick-up/drop-off areas in school zones. Afternoons, around 2:00pm, is considered to be 40% more dangerous than morning times.

Tennessee scored a B- and ranked 22nd in the country. 

Hamilton County scored a D+, ranking 66 out of 81 counties. Bradley County also scored a D+, ranking 68.

Williamson County, south of Nashville, brought of the bottom of the list, ranking 81 out of 81 counties.

Not all of Tennessee's 95 counties were tabulated.

The study found that the more urban the county, the riskier the school roads. The most dangerous time for accidents in school zones is between 4 and 5 p.m.