Route 66 National Historic Trail Designation Act This bill amends the National Trails System Act to designate a trail of approximately 2,400 miles extending from Chicago, Illinois, to Santa Monica, California, as the Route 66 National Historic Trail. The trail must be administered by the National Park Service in a manner that respects and maintains its idiosyncratic nature. The Department of the Interior may not use eminent domain or condemnation in carrying out this bill.