WASHINGTON — The Interior Department is increasing fees at the most popular national parks to $35 per vehicle, backing down from an earlier plan that would have forced visitors to pay $70 per vehicle to visit the Grand Canyon, Yosemite and other iconic parks. A plan announced Thursday would boost fees at 17 popular parks by $5, up from the current $30 but far below the figure Interior proposed last fall. The plan by Interior Secretary Ryan Zinke drew widespread opposition from lawmakers and governors of both parties, who said the higher fees could exclude many Americans from enjoying national parks.