According to the plan released in March, activities that would cease during a shutdown include air traffic controller hiring, field training for controllers and air traffic performance analysis. Travelers to the country’s national parks could see a big impact, affecting some of the most popular tourist destinations in the US. In 2013, an estimated 8 million recreation visits were lost during the 16-day shutdown, according to the association citing National Park Service data. States have also stepped in to keep some national parks open using their own funds. “In the event of a federal shutdown, we are committed to keeping these areas accessible,” the message reads.