The Arizona Department of Transportation says preliminary work started in the past week along 15 miles of Interstate 17.
The state is installing the system because of multiple wrong-way wrecks.
The Transportation Board on July 28 awarded a $1.9 million contract to Mesa-based Contractors West Inc.
Traffic restrictions are scheduled Friday night and Saturday morning at I-17 and Indian School Road so workers can mount thermal cameras, install fiber-optic cable and rewire control cabinets.
The restrictions include closing Indian School Road at I-17 and closing both off-ramps at Indian School Road.
ADOT says future restrictions will be scheduled at other I-17 interchanges between I-10 northwest of downtown Phoenix and Loop 101 in north Phoenix.
