The Idaho Transportation Department says speed limits on rural sections of interstates in the southern part of the state will go up to 80 mph starting Thursday.
That's an increase from 75 mph on rural sections of Interstates 15, 84 and 86. Speed limits for trucks will increase to 70 mph.
The agency says speed limits on interstates in urban areas will remain unchanged at 65 mph.
Speeds will also not increase in northern Idaho.
Agency officials say the speed limits won't increase until signs are put in place.
Lawmakers approved the increases earlier this year.