Drivers in Idaho will see the first change to interstate speed limits in nearly two decades beginning July 1 with an increase on most rural stretches of interstate across Southern Idaho, according to the Idaho Transportation Department.

For the majority of interstates 15, 84, and 86, the speed limit will increase to 80 mph for vehicle traffic and 70 mph for trucks. The speed limit in the urban areas of the Treasure Valley, between Caldwell and east Boise, as well as through Pocatello and Idaho Falls, will remain at 65 mph.

The state said it will work to implement the speed changes on all sections of interstate throughout the day July 1, but some areas of interstate could be delayed until the next day depending on the pace of work or other impacts such as weather.

There are no changes to the 65-mph speed limit on Interstate 90 through northern Idaho at this time.

This is the first statewide increase to the interstate speed limit since an increase from 65 to 75 mph in 1996. The speed limit was raised from 55 mph to 65 mph in the 1980s.

The increased speed limit, approved by the Idaho Legislature during the 2014 session increases the maximum speed limits on interstate highways to 80 mph for vehicles and 70 mph for trucks as deemed appropriate by the ITD.

The law was signed by Gov. Butch Otter on March 18. The 80-mph speed limit is authorized “if the department completes an engineering and traffic study on the interstate highway and concludes that the increase is in the public interest,” according to the law.

"The new speed limit is appropriate for safety and traffic flow," said ITD Chief Operations Officer Jim Carpenter. “Analysis of crash data, existing speed studies and the rural nature of these sections of highway all factored heavily in making these changes.”

ITD said it has been preparing for interstate speed-limit changes by completing the necessary speed studies, engineering reviews, and stockpiling supplies for the one-day change.

The revised speed limit law also allowed for speed-limit increases on state highways to 70 mph. Any increases on state highways will be completed at later dates as engineering studies can be completed, according to the ITD.

Drivers are reminded that the speed limit does not take effect until the signs are posted on each section of roadway. The 75-mph speed limit signs remain enforceable until replaced. The 80-mph speed limit will be legally enforceable immediately upon posting.