FLAGSTAFF, Ariz. — The National Park Service is considering a steep increase in entrance fees at 17 of its most popular parks, mostly in the U.S. West, to address a backlog of maintenance and infrastructure projects.

Visitors to the Grand Canyon, Yosemite, Yellowstone, Zion and other national parks would be charged $70 per vehicle, up from the fee of $30 for a weekly pass. At others, the hike is nearly triple, from $25 to $70.

A 30-day public comment period opened Tuesday. The Park Service says it expects to raise $70 million a year with the proposal at a time when national parks repeatedly have been breaking visitation records and putting a strain on park resources. Nearly 6 million people visited the Grand Canyon last year.

"We need to have a vision to look at the future of our parks and take action in order to ensure that our grandkids' grandkids will have the same if not better experience than we have today," Interior Secretary Ryan Zinke said in a statement. "Shoring up our parks' aging infrastructure will do that."

Annual $80 passes for federal lands would not change, though fees would go up for pedestrians and motorcyclists. The higher fees would apply only during the five busiest contiguous months for parks, for most that's May through September when many families are on vacation.

The proposal would not affect several free weekends and holidays at parks throughout the year.

It comes not long after many of the parks that charge entrance fees raised them. The rationale is the same this time around — to address a backlog of maintenance and infrastructure projects.