The Idaho law goes into effect on July 1, but there could be a delay because the Idaho Transportation Department is still conducting safety surveys to decide where to raise limits. It might be late summer before drivers actually see a change. According to a report from local television news station KMVT, the department actually opposed the bill, but it was pushed through by the state's legislature. Now, the agency has to find a way to implement the change. (Scroll down to watch a video of a KMVT news broadcast explaining the development).
The Wyoming law also begins on July 1, and according to the Casper Star-Tribune, the state's department of transportation is conducting studies to decide where to increase speeds. It hasn't said when changes start. However, the department strongly believes the increase won't cause more accidents, but if it does, then the limits could be lowered.
Currently, Texas has the highest posted speed limit in the country at 85 mph along a 41-mile stretch of toll road between San Antonio and Austin. Texas and Utah have posted 80 mph on some other interstates as well. So if you're in the mood for some higher-speed interstate cruising, the answer is clearer than ever: Go West, young man.