The Arizona Department of Transportation is planning two new "flex" lanes to ease congestion on Interstate 17.
The Arizona Republic reports the lanes will carry people north Fridays and Saturdays, and south on Sundays.
But construction won't begin until 2021 and will take about two years to complete.
The new lanes will run between Black Canyon City and the Sunset Point rest stop in an effort to diminish delays north of Phoenix that sometimes last several hours on the weekends.
Crashes, even minor, clog the roadway as people head north to campsites and cabins on Fridays and Saturdays, and as they head back to the city on Sundays.
The drive between Phoenix and Flagstaff is usually about two hours, but accidents can extend that to four or more.