Traveling at 75 miles an hour, without stopping, it will take you about 11 hours to drive this highway from end to end. Get our free mobile appThe longest highway in Texas almost equals the distance across the entire state from north to south, 880 miles give or take a few. What's The Longest Highway in Texas? The longest interstate highway in Texas is the stretch of I-10 that runs east to west across the state. Keep reading to discover the 50 most popular national parks in the United States, in reverse order from #50 to #1.