As the 20th century progressed, commercial river trade began to decline, and the steamboat era ended, as faster means of transportation became available. Rail lines expanded, automobiles and trucks became reliable, and aircraft soon arrived on the scene. In the postwar period after World War II, numerous major highways were constructed, leading to greater auto travel and commuting. Gallatin County is traversed by I-71, U.S. 42, and U.S. 127. By the 1980s, more than 50 percent of the population was employed outside the county.