A new report from the experts at the Institute for Tourism and Recreation Research confirms what many Montanans already suspected: that the more it costs to access national parks, the fewer people will visit them.

To be precise, for every 10 percent increase in travel costs, monthly park visitation drops by 2.7 percent, according to “Thinking Outside the Park — National Park Fee Increase Effects on Gateway Communities.”

The well-timed report provides a handy measuring stick with which to gauge just how much proposed entrance fee increases would hurt Montana’s tourism economy, especially in the gateway communities closest to Glacier and Yellowstone national parks.

Communities around Yellowstone saw $525 million in spending in 2016, according to the National Park Serice. The tourism institute, housed at the University of Montana, estimates the higher fees will result in an annual loss of $3.4 million to communities within 60 miles of Yellowstone. And that’s only considering one particular fee increase for a seven-day pass. The institute did not study the potential loss to communities near Glacier.

The communities located within 60 miles of Glacier enjoyed more than $250 million in spending from nearly 3 million visitors last year. That spending, according to a National Park Service report, supported 4,300 jobs and more than $117 million in labor income.

But it’s not just local businesses that will feel the loss in tourism spending. Entrance fee increases have a disproportionate impact on those who live closest to Montana’s two world-famous national parks. Those who can least afford it will essentially find themselves locked out of their own back yards.

“The magnitude of visitor effects is proportionate to the necessary distance traveled by the visitor,” the report states. “Entrance fees comprise a smaller fraction of travel costs for international visitors compared to local visitors, thus changes induce a smaller effect on their decisions to travel to a US national park.”

Put another way: higher entrance fees will be a bigger deterrent to Montanans than to tourists from out-of-state. Visitors from Idaho, Montana and Wyoming would have to adjust their vacation budgets by almost 38 percent, while out-of-state visitors from farther away would increase their total budgets by 14 percent, and international visitors only 1 percent.

So not only will higher-priced entrance fees keep more Americans from visiting the national parks that already belong to all Americans, they will most affect those least able to afford a pricey vacation: low-income Montanans.

The national park system was founded on the principle of public ownership and by extension, public access. Beyond the measurable economic benefits Montanans enjoy as neighbors to two treasured national parks, this access is priceless. Indeed, it’s the reason many Montanans choose to make their home in this state.

If U.S. Secretary of the Interior Ryan Zinke was waiting for concrete evidence of the potential harm of hefty fee increases, this report has them in abundance.

The National Park Service, an agency within Zinke’s U.S. Department of the Interior, proposed sizeable increases to the entrance fees collected at 17 of the most popular national parks, including Glacier and Yellowstone, during the “peak season” of May through September.

Among other price hikes, the seven-day fee for a single car will jump from $30 to $70; the per-person fee will double from $15 to $30; and the motorcycle fee will double from $25 to $50.

The National Park Service reasons that it needs to collect more revenue to begin working through its growing backlog of maintenance projects, a backlog now approaching $12 billion. Meanwhile, the National Park Service is facing a 13 percent budget cut – a loss of $3 billion.

The entrance fee increases, however, would scrape together less than $70 million in additional revenue. And even though a fee increase would mean more revenue for the parks, the burden would be borne substantially by surrounding communities.

Early studies by the institute have shown that two out of every three tourism dollars spent in Montana were spent around Glacier or Yellowstone. Glacier Country alone gets a $1 billion boost from tourist spending every year.

Even more people, a record number, have visited Glacier National Park this year: 3.3 million and counting. While that means more entrance fee revenue for the park, it also means more wear and tear on park trails and facilities.

The nation’s most-visited national parks should have the funding they need to pay for regular maintenance, and Zinke should be an outspoken advocate for including that funding in the National Park Service’s budget – not on the backs of Montanans.

Fortunately, there is still time for Montanans to make our own voices heard. The public comment period for the proposed fee increases was extended through Dec. 22. Comment online at https://parkplanning.nps.gov/document.cfm?documentID=83652 or by mail: 1859 C Street NW, Mail Stop: 2346 Washington, D.C. 20240.