Montana Runs 80 for Cars and 70 for Trucks
Date Published
Montana's split is not the widest in the country, but it sits on top of the highest passenger limit, which changes how it feels from the driver's seat.
The truck limit
Mont. Code Ann. 61-8-312 subsection (1) sets the speed limit for a truck or truck tractor of more than one ton manufacturer's rated capacity at 70 miles per hour on an interstate highway, and 65 miles per hour on any other public highway.
Subsection (2) sets a further limit for vehicles under a term permit or in truck-trailer-trailer and truck tractor-semitrailer-trailer-trailer configurations, which are held lower still.
The car limit it is measured against
Mont. Code Ann. 61-8-303 subsection (1)(a) sets the speed limit on an interstate highway outside an urbanized area of 50,000 population or more at 80 miles per hour at all times, and within such an urbanized area at 65.
So on rural interstate the differential is ten miles per hour, from the highest baseline of any split state.
Where the other figures sit
The same section sets 75 during the day and 70 at night on a portion of a national highway of ten miles or more expanded to four lanes and not subject to a permanent special speed zone, 70 day and 65 night on any other public highway, and 25 in an urban district.
Montana also permits a vehicle to exceed the subsection (1) limits by ten miles per hour to overtake and pass, but only while travelling on a two-lane road and in a designated passing zone.
Why the baseline matters
A ten mile per hour gap behind traffic moving at 80 produces more overtaking events per hour than the same gap behind traffic at 70. The differential is what the statute sets; the closing speed is what the driver experiences, and Montana has the highest closing speed of any split-limit state in the country.