Interstate 540 is either of two interstate highway spurs of Interstate 40 in the United States.

Arkansas

In Arkansas, I-540 is a spur to Fort Smith, Arkansas and Bentonville, Arkansas; proposed to become part of an expanded Interstate 49.

The older portion of I-540, completed in the 1970s, connects Interstate 40 to the Oklahoma State Line with Arkansas, going through Van Buren and Fort Smith. This particular spur starts at Exit 7 on Interstate 40 (being seven miles east of the state line with Oklahoma). That point marks mile zero on this spur. The first three miles are through Van Buren, before the bridge over the Arkansas River. The remainder, for a grand total of approximately 15 miles, travels through Fort Smith. What's notable about this is that the mile markers and exit numbers increase from north to south on this spur, and do exactly the opposite, increasing from south to north, on the newer spur (completed c. 1997), connecting Interstate 40 up through Bentonville. Even more interesting, the mileage numbers and exit signs on the newer spur start at 20, as if the zero point were at the Oklahoma state line (the southwest end of the older spur) - this should have meant that all of the exits on the older spur should have been renumbered to match, but this has not occurred (as of November, 2004).

The newer portion of I-540 was completed in the late 1990s. Having been planned since the early 1970s, it created a bypass for the older US Highway 71. It starts at I-40 Exit 12 (12 miles east of the Oklahoma state line, or one mile west of Alma, Arkansas) and continues for over 65 miles, through Crawford County, Arkansas, Washington County, Arkansas and Benton County, Arkansas. Notable cities along the route are Fayetteville, Springdale, Rogers and Bentonville. From I-40 north to Fayetteville, I-540 runs roughly parallel to Highway 71. Just south of Fayetteville, I-540 and Highway 71 combine, forming the major expressway through the Northwest Arkansas metro area (Fayetteville, Springdale, Rogers, and Bentonville). The expressway ends and becomes just Highway 71 again just north of Bentonville, continuing on as the main street of Bella Vista and several miles further to the Missouri border.

One notable fact about I-540 in Arkansas is that the original I-540 spur running from I-540 to Oklahoma through Fort Smith was originally signed east-west, but with the construction of the new spur that runs north through the Northwest Arkansas metro area to Missouri the entire I-540 was resigned as a north-south road. It is one of the few that has changed this way.

North Carolina

In North Carolina, I-540 is the modern perimeter loop of Raleigh, North Carolina. The road is several miles further from downtown Raleigh than Interstate 440, the Cliff Benson Beltline. Known formally as the Northern Wake Expressway, the "Outer Loop" presently runs from I-40 near Raleigh-Durham International Airport around the northern part of Raleigh to US 1 (Capital Boulevard) northeast of Raleigh.

As of 2004, sections from US 1 to US 64 in Knightdale, North Carolina in the east and sections from I-40 to NC 54 and NC 55 is the east are under construction. Work on the southern portion of the beltway has not been begun at this time and the final segments may not be open until 2030. When finished, the loop will total over 50 miles in length; as of 2004, only about one quarter of the project has been completed and is open to traffic.

Original NCDOT plans were to renumber I-540 to I-640 once the Outer Loop was completed.