The United States Border Patrol operates 71 traffic checkpoints, including 33 permanent traffic checkpoints, near the Mexico–United States border.[1][2] The stated primary purpose of these inspection stations is to deter illegal immigration and smuggling activities. After the September 11 attacks in 2001, they took on the additional role of terrorism deterrence.[citation needed] These checkpoints are located between 25 and 75 miles (40 and 121 km) of the Mexico–United States border along major U.S. highways; near the southern border of the contiguous United States. Their situation at interior locations allow them to deter illegal activities that may have bypassed official border crossings along the frontier. The checkpoints are divided among nine Border Patrol sectors. There are a number of these checkpoints near the northern border of the contiguous U.S. as well (such as in the states of New York or Maine), within 100 miles (160 km) of the Canada–U.S. border.[3]