U.S. Route 40 (US 40) runs east–west across south central Illinois for 159.8 miles (257.2 km). US 40 enters the state from Missouri across the Poplar Street Bridge over the Mississippi River at East St. Louis concurrent with Interstate 55 (I-55) and I-64 and exits just south of State Line, Indiana, running concurrently with I-70. For the majority of its route through Illinois, US 40 follows the National Road, including the route's initial western terminus at Vandalia.