HELENA, Mont. — The Montana Department of Transportation (MDT) recently extended the 65 miles per hour (mph) speed zone on Interstate 15 (I-15). The speed zone now begins half a mile south of the South Hills Interchange (Exit 190).
This change is in response to the new urban area boundaries approved by the Federal Highway Administration (FHWA). In accordance with Montana Law (MCA 61-8-303 (a)), interstate speed limits must be reduced to 65 mph in urban areas with populations over 50,000. The population within the new boundary exceeds this threshold.
The change was approved by the Montana Transportation Commission on December 11, 2025, per MCA 61-8-309.
The public is encouraged to contact MDT Traffic and Safety Engineer Gabe Priebe at 406-444-9252 or Lead Investigations Engineer Brenden Borges at 406-444-6255 with questions or comments about the speed limit reduction.
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