New Idaho Law Equalizes Speed Limits for Trucks and Passenger Vehicles on State Highways
A new Idaho transportation law signed by Governor Brad Little will eliminate the long-standing speed difference between commercial trucks and passenger vehicles on Idaho state highways and interstates, a change that affects thousands of Ada County commuters and commercial drivers who travel corridors including Interstate 84 through the Treasure Valley. House Bill 664, signed into law on March 24, 2026, allows large commercial trucks to travel at the same posted speed limits as passenger cars — up to 80 miles per hour on rural stretches of Idaho’s interstate system.
Background: Idaho’s Highway Speed Disparity
For years, Idaho maintained a two-tiered speed limit system on its highways. Passenger vehicles could travel up to 80 miles per hour in rural interstate zones, while commercial trucks — defined under the new law as vehicles with five or more axles and a gross weight exceeding 26,000 pounds — were capped at 65 miles per hour regardless of the posted limit for other traffic.
Critics of the old system argued the 15-mile-per-hour gap between trucks and passenger cars created genuinely dangerous conditions, particularly on rural stretches of Idaho’s interstate network where traffic moves fast and overtaking maneuvers are frequent. When faster passenger vehicles repeatedly pass slower-moving freight trucks, the number of lane changes and close interactions between vehicles increases — a dynamic that traffic safety researchers have long associated with higher collision risk.
Idaho was among eight states that previously maintained a speed differential between trucks and passenger vehicles. Supporters of House Bill 664 contended that equalizing the limits brings Idaho in line with the majority of western states and reflects modern research on traffic flow.
Key Details of House Bill 664
Under the new Idaho law, commercial trucks meeting the five-axle and 26,000-pound weight threshold may now travel at the same posted speed limit as passenger vehicles. In practice, that means:
On rural Idaho interstates, commercial trucks can now legally travel up to 80 miles per hour, matching the passenger vehicle limit that has been in place for years. On more urbanized corridors — including the segments of Interstate 84 connecting Caldwell, Nampa, and Boise through Ada County — the shared speed limit remains 65 miles per hour.
The bill passed the Idaho House on March 3, 2026, before moving to the Idaho Senate, where it passed by a decisive 27 to 7 margin on March 17. Governor Little signed the measure into law one week later on March 24.
The legislation directly affects commercial drivers who regularly haul cargo through Idaho on Interstates 84, 86, and 15 — three of the Mountain West’s most heavily traveled freight corridors and routes that see significant daily volume through Ada County and the broader Treasure Valley region.
Impact on Ada County Residents and Treasure Valley Commuters
For Ada County residents, the most immediate effect of the new law applies to the urban interstate segments through Boise, Meridian, Garden City, and the surrounding Treasure Valley. On those stretches, where the posted limit is already 65 miles per hour, the practical change for daily commuters will be minimal — trucks were already operating near that limit, and the new law simply removes the legal distinction between vehicle classes at that speed.
The larger impact will be felt on rural sections of Idaho’s interstate system beyond Ada County, where freight haulers will now be able to maintain 80 miles per hour alongside passenger traffic rather than being restricted to 65. Supporters argue this will reduce the speed differential that prompted dangerous passing situations, improve the overall flow of commercial freight, and help keep supply chain costs competitive for Idaho businesses.
Idaho’s economy depends heavily on freight movement, and the Treasure Valley serves as a major distribution hub for goods moving through the Pacific Northwest and Mountain West. Reducing delays and improving predictable travel times for commercial carriers can have downstream effects on the cost of goods delivered to Ada County retailers, manufacturers, and agricultural operations.
What Comes Next
House Bill 664 was signed into law on March 24, 2026, and the new speed equalization provisions are now in effect as part of Idaho state law. Commercial truck drivers operating on Idaho interstates and state highways should familiarize themselves with the updated limits for both rural and urban corridors.
Ada County motorists who regularly travel Interstate 84 through Boise and Meridian should be aware that large commercial trucks are now legally authorized to travel at the same posted limits as passenger vehicles. The Idaho Transportation Department is the primary agency responsible for posting and enforcing speed limits statewide. Residents with questions about specific highway segments or enforcement procedures can contact ITD directly at itd.idaho.gov or reach out to the Idaho State Police, which handles speed enforcement on Idaho’s interstate system.