Idaho law lets heavy trucks hit 80 mph on interstate sections

Heavy trucks will be able to run 80 mph on Idaho interstate sections starting July 1, and in Kootenai County the change lands on a corridor already strained by road work, commuter traffic and summer freight. The sharpest local pinch point is Interstate 90 over Fourth of July Pass, where drivers are already slowing for a major construction zone between Wolf Lodge and the east side of the pass.

Gov. Brad Little signed House Bill 664 on March 23, 2026, ending the old speed split between passenger vehicles and semi-trucks on those interstate sections. Supporters argued that the bigger danger is not speed alone, but the difference in speed between vehicles. The bill cites research saying a 10 mph speed differential can raise dangerous vehicle interactions by as much as 227%.

For drivers in and around Coeur d'Alene, Post Falls and Hayden, the change will be most visible on I-90, where faster truck traffic will now blend into a lane already crowded by commuters, freight rigs and recreation traffic. A truck driver interviewed by Idaho News 6 said many trucks are already governed to about 65 to 68 mph, which means the new law may narrow the gap between semis and surrounding traffic rather than create a brand-new pace on the road.

The timing matters in Kootenai County because the Idaho Transportation Department says the Fourth of July Pass project is in its final season. The $31.5 million project covers eight miles of I-90 between Wolf Lodge and the east side of Fourth of July Pass. Through the work zone, the speed limit is 45 mph, traffic is limited to one lane in each direction and oversized loads are restricted at all times.

That makes the July 1 rollout more than a statewide policy shift. In North Idaho, it will collide with construction delays, tighter passing opportunities and a summer travel season when I-90 already carries a heavy mix of freight, commuters and vacation traffic. State leaders say the law should simplify traffic flow, but local motorists are likely to judge it by what they feel on the pavement: shorter following distances, more pressure in work zones and a fresh round of anxiety about how 80-mph trucks will behave beside passenger cars.