Interior Secretary Ryan Zinke told the Senate Energy and Natural Resources Committee on Tuesday morning that the Interior Department is considering raising fees at the most-visited national parks, partially because groups of people such as veterans, the disabled and the elderly can enter parks for free.

“When you give discounted [rates] to the elderly, veterans, and the disabled and do it by the carload, not a whole lot people actually pay at our front door,” Zinke said. “One person with a pass and everyone comes in for free. We are looking at ways to have more revenue at the front door at our parks.”

He stood by the idea to raise fees at 17 popular parks, despite bipartisan criticism, although he emphasized Interior has not made a final decision on whether to move forward.

“Parks fees won’t address the $11.7 billion [maintenance backlog at national parks] but a lot have record visitation and we are looking at many options, and one is during peak season raising the rate. We have not yet concluded that.”

Under the proposal, the entrance fee for the Grand Canyon and other parks would jump from $30 to $70 per vehicle. Other parks would see even bigger increases, from $25 to $70, during the busiest months. Zion and Arches in Utah, for example, would impose those fees from May through September, while Maine's Acadia and Virginia's Shenandoah national parks would charge the higher prices in June through October.

Sen. Maria Cantwell of Washington, the top Democrat on the committee, said that is the wrong approach.

"While my constituents are hearing about private jet rides and expensive doors, they want to understand why someone is proposing to raise park fees at this level,” Cantwell said Tuesday morning. "We should be increasing access," to national parks, she said.

Zinke also said too much of the visitor fees to national parks go to Washington and he would like to give individual parks more discretion on how to use the money.

"Part of the value of entrance fees is we want to push more flexibility to the park itself," Zinke said. "We want to make sure the parks remain of value and accessible for America. That is the promise we will make. I am aware an increase hurts some families, and our interest is not to hurt families."

Zinke touted his separate proposal, backed by bipartisan bills in Congress, to create a fund to pay for the repairs and maintenance needed in national parks and wildlife refuges.

The fund, which would hold up to $18 billion, would be paid for by new leases for energy development on onshore and offshore federal lands. The Interior Department has a $16 billion maintenance backlog, the agency says. Of that amount, the National Park Service has the largest share, $11.6 billion in 2017.

“This is the largest investment in our public lands infrastructure in our nation's history,” Zinke said. “Our public lands are our greatest treasures but have suffered major neglect over the years.”

Zinke said says the maintenance backlog could be closed in eight years with his energy fund proposal.

The commitment to fixing infrastructure, Zinke said, shows how the agency will focus its second year on traditional responsibilities of conservation, after Democrats have criticized the agency’s efforts to boost energy development on public lands and waters.

“This budget recognizes American strength relies on American energy,” Zinke said in his opening statement. “Last year was about energy. This year a pivot to conservation, infrastructure and reorganization.”