Testing has begun at three spots in metro Phoenix for devices that are aimed at detecting wrong-way drivers.
The test is part of a larger effort by state transportation officials to reduce wrong-way crashes.
Over the last year, metro Phoenix has experienced a rash of wrong-way accidents on freeways.
The system of radar and camera sensors sets off red lights on two wrong-way signs when a person is driving in the wrong direction.
It also alerts transportation officials and the Arizona Department of Public Safety of such incidents.
The system was installed last week on the northbound exit at Interstate 17 exit to the Carefree Highway, the eastbound Interstate 10 exit at Ray Road and the northbound Loop 101 off ramp at Thunderbird Road.