ACADIA NATIONAL PARK, Maine — Visits to Maine’s only national park so far this year are on pace to exceed the total from 2017, when Acadia had an estimated record of 3.5 million visits, according to park officials. The number of visits — how many times someone enters the park, even if one person might do it many times during the year — is estimated to have been slightly ahead for July and August this summer than it was for the same two months in 2017.