Sensors installed at three Interstate 40 locations west of Flagstaff are helping the Arizona Department of Transportation (ADOT) forecast the likelihood of ice forming and respond accordingly.

The combination of freezing temperatures and moisture means ice can form overnight in Arizona’s high country. It is an especially big challenge on I-40 between Ash Fork and Flagstaff, which is above 6,000 ft in most places and sees heavy use by commercial and passenger vehicles.

“Technology can provide us with another way to keep motorists safe as they travel to Arizona’s colder regions,” said Audra Merrick, district engineer for ADOT’s North Central District. “These sensors are another tool in ADOT’s toolbox to help keep the highways clear of snow and ice during winter season.”

The roadway sensors, positioned just west of Flagstaff, just west of Williams and on Ash Fork Hill, are connected to ADOT Road Weather Information System (RWIS) locations, which use cameras and instruments to provide the latest conditions. Each location has one sensor measuring the salt content of road surface moisture, which affects the freezing point, and another measuring the temperature of the ground underneath.

A computer program combines this information with data from the RWIS and National Weather Service to forecast the likelihood of ice forming, helping ADOT determine whether to send crews out to lay deicing material. The program can also alert operators if the pavement temperature drops below a certain threshold.

The three sensors on I-40 cost $90,000 and were funded through ADOT maintenance funds. ADOT plans to install sensors at additional high-country roadway locations over the next few years.