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A proposal to convert nearly 1,800 miles of U.S. Highway 287 into a designated interstate highway has drawn attention from transportation advocates and wildlife researchers alike, with the route passing through some of the most ecologically sensitive terrain in the American West — including stretches of Montana where animal-vehicle collisions are among the most frequent in the region.
Why It Matters
Highway 287 runs from Choteau, Montana, in the north all the way to Port Arthur, Texas — a span of roughly 1,791 miles — passing through Idaho, Wyoming, Colorado, and Oklahoma along the way. For Montanans, the highway cuts through the Greater Yellowstone ecosystem, a landscape home to 67 mammal species, several hundred bird species, and thousands of native plants.
The proposal would bring significant infrastructure upgrades to a corridor that serves both local communities and long-distance travelers. But researchers who study wildlife movement warn that widening and upgrading the road could worsen an already serious problem with animal-vehicle collisions along the route.
What Happened
U.S. Senator Cynthia Lummis of Wyoming introduced legislation on May 11 to redesignate U.S. Highway 287 as a federal interstate. The bill, known as the “I-47 Future Interstate Act” and numbered S. 4484, was referred to the Senate Committee on Environment and Public Works. Senator John Cornyn of Texas signed on as a cosponsor.
The legislation calls for the highway to be widened with additional lanes, a center median, broader shoulders, and the construction of on- and off-ramps consistent with interstate highway standards. Proponents argue that upgrading the route would improve safety and increase connectivity across the central portion of the country.
In Montana, a coalition called Madison Passages formed in late 2025 to raise public awareness about safety conditions along U.S. 287, reflecting growing local concern about how traffic levels on the highway affect both drivers and wildlife.
By the Numbers
- 1,791 miles — total length of U.S. Highway 287 from Choteau, Montana to Port Arthur, Texas
- $1.6 billion per year — estimated cost of wildlife-vehicle collisions across Western states
- 300 times — how much less likely pronghorn are to cross an interstate compared to a state highway, according to a 2021 study in the Journal of Wildlife Management
- 3,500 to 5,000 AADT — the annual average daily traffic range at which a road transitions from a significant barrier to a near-complete barrier for pronghorn movement
- 4,000+ AADT — traffic volumes already recorded on some roads in the Madison Valley
Wildlife and Ecology Concerns
A 2023 study found that several stretches of U.S. 287 — particularly between Lander and Moran in Wyoming, and north of Three Forks and Helena in Montana — rank in the top 10 percent of Western U.S. roads for wildlife-vehicle collision frequency.
Andrew Jakes, a senior research scientist with the Wyoming Migration Initiative, described the cumulative effect of road expansion on wildlife as “death by a thousand cuts,” warning that incremental infrastructure changes can compound to produce lasting disruption to animal migration patterns.
Road ecologist Liz Fairbank of the Center for Large Landscape Conservation noted the specific thresholds at which traffic volume becomes determinative. “At 5,000 AADT, the road can be a complete barrier,” she said, pointing out that pronghorn — one of North America’s most iconic migratory species — are particularly sensitive to road upgrades. Some Madison Valley roads already exceed 4,000 AADT, placing them close to the threshold where wildlife movement becomes severely restricted.
The Greater Yellowstone region has become an economic and tourism asset for Montana, and major industrial investment projects like the Janicki Industries plant in Great Falls signal that the state’s transportation infrastructure is under increasing demand. How policymakers balance economic development with conservation obligations will likely shape the debate over S. 4484 as it moves through committee.
What’s Next
The bill remains in committee, and no vote has been scheduled. Wildlife researchers and regional stakeholders are expected to weigh in as the Senate Environment and Public Works Committee reviews the proposal. The outcome could set a precedent for how the federal government approaches highway upgrades in ecologically sensitive corridors across the Mountain West.
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