CMV Speed Limit: New Idaho Law Ends Restrictions for Trucks

Idaho CMV Speed Limit Law Changes for Heavy Trucks

A new law passed by the Legislature of the State of Idaho is set to change how the speed limit applies to certain commercial motor vehicles (CMVs). House Bill 664 updates state law to align speed limits for heavier trucks with those of other motorists under specific conditions.

The change is expected to impact commercial truck drivers operating in Idaho, especially those driving vehicles with five or more axles and a higher gross weight.

Idaho CMV Speed Limit Now Matches Other Vehicles

The most important update in the new law removes a previous rule that required some heavy trucks to travel at lower speeds than other traffic.

Under the updated statute, vehicles with five or more axles and a gross weight of more than 26,000 pounds will now follow the same speed limit as other motor vehicles.

This change removes the separate speed standard that once applied to heavier trucks in certain areas.

Speed Limit Still Based on Posted Speeds

While the law changes how the CMV speed limit applies, it does not change the posted speed limits on Idaho roads.

The updated law keeps the following maximum speeds in place:

• 75 miles per hour on interstate highways, unless otherwise posted
• Up to 80 miles per hour on interstates if approved through engineering and traffic studies
• 65 miles per hour on state highways, with the potential to increase to 70 miles per hour
• 55 miles per hour in other areas, unless posted differently
• 35 miles per hour in residential, business, or urban districts

These limits now apply equally when determining the speed limit for qualifying commercial vehicles.

Idaho Removes Lower Speed Requirement

The law removes earlier language that required heavier trucks to travel below the speeds allowed for lighter vehicles.

The revised statute states that the maximum lawful speed for vehicles with five or more axles and a gross weight over 26,000 pounds “shall be the same” as for lighter vehicles.

This update simplifies the CMV speed limit by eliminating different rules based on vehicle size and weight.

Passing Rules and CMV Speed Limit Remain Separate

The law keeps existing rules about passing. These rules allow certain drivers to exceed the posted speed limit by up to 15 miles per hour when passing another vehicle under specific conditions.

This passing rule applies only in limited situations, including:

• Two-lane roads with one lane in each direction
• Roads with a speed limit of 55 miles per hour or higher
• Designated passing lanes

The rule does not apply in construction zones or on lower-speed roads.

These provisions are separate from the CMV speed limit changes in the new law.

Safe Driving Rules Still Apply to CMV Speed Limit

Even with the updated CMV speed limit, Idaho law still requires all drivers to operate at a safe speed based on current conditions.

Drivers must consider:

• Traffic
• Weather
• Road conditions
• Visibility
• Other hazards

This means truck drivers must slow down when conditions make it unsafe to travel at higher speeds, even if the posted speed limit allows it.

What the Speed Limit Change Means for Drivers

The updated CMV speed limit law may affect how commercial drivers operate across Idaho.

More Consistent Highway Speeds

Heavy trucks can now travel at the same speeds as other vehicles. This may reduce speed differences and improve traffic flow.

Fewer Speed Adjustments

Drivers will no longer need to follow separate lower speed limits for heavy trucks in certain areas.

Continued Focus on Safety

Drivers are still required to adjust speed based on conditions. The basic rule of safe driving remains in place.

No Increase in Posted Limits

The law does not raise speed limits. It only changes how the speed limit applies to certain vehicles.

Law Takes Effect July 2026

The law includes an emergency clause and is set to take effect on July 1, 2026.

Once in effect, the updated CMV speed limit rules will apply statewide.

Summary of Idaho CMV Speed Limit Changes

House Bill 664 updates Idaho law by aligning the speed limit for heavier commercial vehicles with the limits set for other drivers.

The law removes lower speed requirements for trucks with five or more axles and a gross weight over 26,000 pounds. However, it does not change posted speed limits or reduce safety expectations.

For truck drivers, the update may lead to more consistent travel speeds while maintaining the need for safe and careful driving.