According to 36 U.S.C. § 120, on National Defense Transportation Day, the president urges "the people of the United States, including labor, management, users, and investors, in all communities served by the various forms of transportation to observe National Defense Transportation Day by appropriate ceremonies that will give complete recognition to the importance to each community and its people of the transportation system of the United States and the maintenance of the facilities of the system in the most modern state of adequacy to serve the needs of the United States in times of peace and in national defense."
On May 16, 1957, Congress designated the third Friday of May each year as National Defense Transportation Day. In 1962 Congress included the whole week within which the Friday falls as National Transportation Week.
(federal) = federal holidays, (state) = state holidays, (religious) = religious holidays, (week) = weeklong holidays, (month) = monthlong holidays, (36) = Title 36 Observances and Ceremonies Bolded text indicates major holidays that are commonly celebrated by Americans, which often represent the major celebrations of the month.