Auxiliary Interstate Highway in the context of Interstate 95

Interstate 345 (I-345) is an unsigned 1.4-mile-long (2.3 km) Auxiliary Interstate Highway in the city of Dallas within the US state of Texas. It is a freeway that connects I-45 (which ends at the interchange with I-30) with U.S. Highway 75 (US 75; North Central Expressway) at State Highway Spur 366 (Spur 366; Woodall Rodgers Freeway). Few maps actually display the road as I-345; signposts on the road show US 75 northbound, while southbound the highway is signed as I-45. In recent years, a debate over whether to maintain or decommission I-345 has received increased attention from several Dallas media outlets. TxDOT elected to maintain the freeway by lowering it below ground and removing frontage roads.

Interstate 290 (I-290) is an auxiliary Interstate Highway that runs westward from the Jane Byrne Interchange near the Chicago Loop. The portion of I-290 from I-294 to its east end is officially called the Dwight D. Eisenhower Expressway. In short form, it is known as "the Ike" or the Eisenhower. Before being designated the Eisenhower Expressway, the highway was called the Congress Expressway because of the surface street that was located approximately in its path and onto which I-290 runs at its eastern terminus in the Loop.

I-290 connects I-90 (Jane Addams Memorial Tollway) in Rolling Meadows with I-90/I-94 (John F. Kennedy Expressway/Dan Ryan Expressway) near the Loop. North of I-355, the highway is sometimes known locally as Illinois Route 53 (IL 53), or simply Route 53, since IL 53 existed before I-290. However, it now merges with I-290 at Biesterfield Road. In total, I-290 is 29.84 miles (48.02 km) long.

Interstate 678 (I-678) is a north–south auxiliary Interstate Highway that extends for 14 miles (23 km) through two boroughs of New York City. The route begins at John F. Kennedy International Airport on Jamaica Bay and travels north through Queens and across the East River to the Bruckner Interchange in the Bronx, where I-678 ends and the Hutchinson River Parkway begins.

I-678 connects to I-495 (the Long Island Expressway) in Flushing Meadows–Corona Park. The highway is known as the Van Wyck Expressway (/væn ˈwɪk/ van WIK or /væn ˈwaɪk/ van WYKE) from JFK Airport to Northern Boulevard (New York State Route 25A or NY 25A), the Whitestone Expressway from NY 25A north to the Bronx–Whitestone Bridge, and the Hutchinson River Expressway from the bridge to the Bruckner Interchange. North of the interchange, I-678 ends and the roadway continues as the Hutchinson River Parkway.

Route 110, consisting of State Route 110 (SR 110) and Interstate 110 (I-110), is a state and auxiliary Interstate Highway in the Los Angeles metropolitan area of the US state of California. The entire route connects San Pedro and the Port of Los Angeles with Downtown Los Angeles and Pasadena. The southern segment from San Pedro to I-10 in downtown Los Angeles is signed as I-110, while the northern segment to Pasadena is signed as SR 110. The entire length of I-110, as well as SR 110 south of the Four Level Interchange with US Route 101 (US 101), is the Harbor Freeway, and SR 110 north from US 101 to Pasadena is the historic Arroyo Seco Parkway, the first freeway in the western United States.

Interstate 295 (I-295) is an auxiliary Interstate Highway within New York City. Measuring 7.7 miles (12.4 km) in length, I-295 originates at NY 25 (Hillside Avenue) in Queens, running north across Queens and over the tolled Throgs Neck Bridge, to Bruckner Interchange, a junction with I-95, I-278, I-678, and the Hutchinson River Parkway in the Bronx. From south to north, I-295 intersects the Grand Central Parkway, I-495 (Long Island Expressway), and the Cross Island Parkway in Queens before crossing the Throgs Neck Bridge and splitting with I-695 (Throgs Neck Expressway). In Queens, I-295 is also known as the Clearview Expressway, and in the Bronx, parts are known as the Throgs Neck Expressway and the Cross Bronx Expressway Extension.

The entirety of I-295 was proposed in 1955 as a part of I-78. Construction started in 1957, and the highway opened in 1963 with the I-78 designation. Originally, plans called for I-78 to be extended southeastward from the Holland Tunnel in Manhattan to NY 878 (Nassau Expressway) in Queens, before curving north to meet the Clearview Expressway. These plans were canceled in 1970, at which point the highway between NY 25 in Queens and I-95 in the Bronx was re-designated as I-295. I-295 was originally planned to continue further south to John F. Kennedy International Airport. The 2.5-mile (4.0 km) JFK Expressway, constructed in the 1980s, was intended to be part of I-295 but was constructed only as far north as the Belt Parkway.

Interstate 580 (I-580) is an approximately 76-mile-long (122 km) east–west auxiliary Interstate Highway in Northern California. The heavily traveled spur route of I-80 runs from US Route 101 (US 101) in San Rafael in the San Francisco Bay Area to I-5 at a point outside the southern city limits of Tracy in the Central Valley. I-580 forms a concurrency with I-80 between Albany and Oakland, the latter of which is the location of the MacArthur Maze interchange immediately east of the San Francisco–Oakland Bay Bridge. I-580 provides a connection from the Bay Area to the southern San Joaquin Valley and Southern California via I-5, as I-5 bypasses the Bay Area to the east.

A portion of I-580 is called the MacArthur Freeway, after General Douglas MacArthur. Other portions are named the John T. Knox Freeway (after a former speaker pro tempore of the California State Assembly), the Eastshore Freeway (after its location on San Francisco Bay), the Arthur H. Breed Jr. Freeway (after a former California State assemblyperson and senator—the stretch itself lying between the cities of Castro Valley and Dublin), the William Elton "Brownie" Brown Freeway (after a Tracy resident instrumental in determining the route of I-5 through the San Joaquin Valley), the Sgt. Daniel Sakai Memorial Highway (after the Castro Valley resident and Oakland SWAT officer killed in the 2009 shootings of Oakland police officers), and the John P. Miller Memorial Highway (after the Lodi resident and California Highway Patrol officer killed while chasing down a DUI driver).

Interstate 495 (I-495) is an auxiliary Interstate Highway in southeastern New York state. It is jointly maintained by the New York State Department of Transportation (NYSDOT), the New York City Department of Transportation (NYCDOT), MTA Bridges and Tunnels (TBTA), and the Port Authority of New York and New Jersey (PANYNJ). East of the Queens–Midtown Tunnel, I-495 is known as the Long Island Expressway (LIE).

Spanning approximately 66 miles (106 km), I-495 traverses Long Island from the western portal of the Queens–Midtown Tunnel in the New York City borough of Manhattan to County Route 58 (CR 58) in Riverhead in the east. I-495 intersects with I-295 in Bayside, Queens, through which it connects with I-95. The 2017 route log erroneously shows the section of highway between I-278 in Long Island City and I-678 in Corona as New York State Route 495 (NY 495).

Interstate 270 (I-270) is a 34.7-mile (55.8 km) auxiliary Interstate Highway in the U.S. state of Maryland that travels from I-495 (Capital Beltway) just north of Bethesda in Montgomery County north to I-70 in the city of Frederick in Frederick County. It consists of the 32.6-mile (52.5 km) mainline as well as a 2.1-mile (3.4 km) spur that provides access to and from southbound I-495. I-270 is known as the Washington National Pike, and makes up the easternmost stretch of the Dwight D. Eisenhower Highway. Most of the southern part of the route in Montgomery County passes through suburban areas around Rockville and Gaithersburg that are home to many biotech firms. This portion of I-270 is up to 12 lanes wide and consists of a local–express lane configuration as well as high-occupancy vehicle lanes (HOV lanes) that are in operation during peak travel times. North of the Gaithersburg area, the road continues through the northern part of Montgomery County, passing Germantown and Clarksburg as a six- to eight-lane highway with an HOV lane in the northbound direction only. North of here, I-270 continues through rural areas into Frederick County and toward the city of Frederick as a four-lane freeway.

The freeway was built between 1953 and 1960 as the Washington National Pike between Bethesda and Frederick and carried U.S. Route 240 (US 240), which was rerouted off what is now Maryland Route 355 (MD 355) between these two points. With the creation of the Interstate Highway System a few years later, the road was designated as I-70S along with US 240. There were plans to extend I-70S to I-95 in Washington, D.C., on the North Central Freeway from the Capital Beltway; however, they were canceled in the 1970s due to opposition from residents in the freeway's path. The concurrent US 240 designation was removed in 1972 and I-70S became I-270 in 1975. Increasing traffic levels led to a $200-million (equivalent to $509 million in 2024) widening of the road in Montgomery County to its current configuration. Many improvements are slated for I-270, including the widening of the route that would add high-occupancy toll lanes (HOT lanes).

Interstate 295 (I-295) also known as the Anacostia Freeway, is a six-mile (9.7 km) auxiliary Interstate Highway in the US state of Maryland and in Washington, D.C. It connects I-95/I-495 and Maryland Route 210 (MD 210; Indian Head Highway) near the Potomac River (just outside DC's boundary with Maryland) to I-695 and District of Columbia Route 295 (DC 295) in the Anacostia neighborhood of Washington, D.C.

Interstate 695 (I-695), also known as the Southeast Freeway, is a two-mile-long (3.2 km) auxiliary Interstate Highway in Washington, D.C. It travels from an interchange with I-395 south of the US Capitol building east then south across the 11th Street Bridges to an interchange with I-295 and District of Columbia Route 295 (DC 295) in Anacostia.

Access also exists from eastbound I-695 to Pennsylvania Avenue at Barney Circle, just northwest of the John Philip Sousa Bridge. Stub ramps at Pennsylvania Avenue, once meant to continue the freeway (as part of I-295) to I-95 and US Route 50 (US 50) northeast of Washington Union Station, now provide access to Robert F. Kennedy Memorial Stadium.

Interstate 535 (I-535) is a 2.78-mile-long (4.47 km) auxiliary Interstate Highway spur route of I-35 in the US states of Minnesota and Wisconsin. It is paired with U.S. Highway 53 (US 53) along its entire route. The Interstate was part of the original 1956 Interstate Highway System and was completed in 1971. Since then, weight limits have been added to the Blatnik Bridge that carries the highway over Saint Louis Bay between Superior, Wisconsin, and Duluth, Minnesota.

Interstate 375 (I-375) is a north–south auxiliary Interstate Highway in Detroit, Michigan, United States. It is the southernmost leg of the Walter P. Chrysler Freeway and a spur of I-75 into Downtown Detroit, ending at the unsigned Business Spur I-375 (BS I-375), better known as Jefferson Avenue. The freeway opened on June 12, 1964. At only 1.062 miles (1.709 km) in length, it once had the distinction of being the shortest signed Interstate Highway in the country before I-110 in El Paso, Texas, was signed. The Michigan Department of Transportation (MDOT) announced in 2021 plans to convert the freeway to a boulevard. Details of that project were revealed in April 2023 with MDOT reaffirming that construction is scheduled to begin in 2025.

Interstate 394 (I-394) is a short east–west auxiliary Interstate Highway in Hennepin County in the US state of Minnesota. It is also commonly referred to by its pre-1991 name, Wayzata Boulevard, and by its other designation for most of its route, US Highway 12 (US 12). It runs for 9.8 miles (15.8 km) from downtown Minneapolis to I-494 in the Minneapolis suburb of Minnetonka. At its western terminus, the roadway loses its Interstate designation but continues as US 12. I-394 serves as the most direct link for commuters and other drivers who are traveling between downtown Minneapolis and parts of the western Minneapolis–Saint Paul metropolitan area.

I-394 maintains at least three lanes in each direction except under the Minnesota State Highway 100 (MN 100) interchange and also between I-94/US 52 and its eastern terminus downtown.

Interstate 494 (I-494) is an auxiliary Interstate Highway making up part of a beltway of I-94, circling through the southern and western portions of the Minneapolis–Saint Paul metropolitan area in Minnesota. The 42.94-mile (69.11 km) road is coupled with I-694 (which circles the northern edge of the Twin Cities metro area) at each end and composes more than half of the major beltway of the region. I-694/I-494 also act as loop routes for I-35E and I-35W.

The speed limit on I-494 is 60 mph (97 km/h). Interstate Highways outside of the loop in Minnesota may be signed as high as 70 mph (110 km/h). Most highways inside the loop are signed at speeds of 55 mph (89 km/h) or lower, though a few exceptions were added in September 2005, allowing speeds of up to 60 mph (97 km/h) in some places. Those roads had been signed at 60 mph (97 km/h) or higher up until the 1973 oil crisis.

Interstate 694 (I-694) is an east–west auxiliary Interstate Highway located in the Minneapolis–Saint Paul metropolitan area in the US state of Minnesota. The western terminus of the route is at its junction with I-94, I-494, and US Highway 52 (US 52) in Maple Grove. The eastern terminus of I-694 is at its junction with I-94 and I-494 at the Woodbury–Oakdale city line. I-694 comprises the northern and northeastern portions of a beltway around the Twin Cities, with I-494 forming the remainder of the beltway. The speed limit is 60 mph (97 km/h). Interstate Highways outside of the loop in Minnesota may be signed as high as 70 mph (110 km/h) but can only reach 60 mph (97 km/h) inside the loop.

I-694 also interchanges with I-35W at New Brighton–Arden Hills and I-35E at Little Canada–Vadnais Heights. I-694 is also concurrent with I-94/US 52 for eight miles (13 km) from Maple Grove to Brooklyn Center. I-694 is 30.8 miles (49.6 km) in length.

The Massachusetts Turnpike (colloquially the "Mass Pike" or "the Pike") is a controlled-access toll road that runs concurrently with Interstate 90 (I-90) in the U.S. state of Massachusetts. It is the longest Interstate Highway in Massachusetts, spanning 138 miles (222 km) along an east–west axis.

The turnpike opened in 1957, and it was designated as part of the Interstate Highway System in 1959. It begins at the New York state line in West Stockbridge, linking with the Berkshire Connector portion of the New York State Thruway. The original western terminus of the turnpike was located at Route 102 in West Stockbridge before I-90 had been completed in New York state. The turnpike intersects with several Interstate Highways as it traverses the state, including I-91 in West Springfield; I-291 in Chicopee; I-84 in Sturbridge; the junction of I-290 and I-395 in Auburn; and I-495 in Hopkinton. The eastern terminus of the turnpike was originally at Route 128 (now cosigned with I-95) in Weston, and has been extended several times: to Allston in 1964, to the Central Artery (at the time designated as I-95/Route 3; currently designated as I-93/US 1/Route 3) in Downtown Boston in 1965, and to Route 1A in East Boston as a route to Logan International Airport in 2003 as part of the "Big Dig" megaproject. I-190 and I-290 are the two auxiliary Interstate Highways that serve the route.