Interstate Highways have the highest speed limits and the highest traffic numbers. Interstates are numbered in a grid: even-numbered routes for east–west routes (with the lowest numbers along Mexico and the Gulf of Mexico), and odd-numbered routes are north–south routes (with the lowest numbers along the Pacific Ocean). Three-digit Interstates are, generally, either beltways or spurs of their parent Interstates (for example, Interstate 510 is a spur into the city of New Orleans, Louisiana, and is connected to Interstate 10).
U.S. Numbered Highways are the original interstate highways, dating back to 1926. U.S. Highways are also numbered in a grid: even numbered for east–west routes (with the lowest numbers along Canada) and odd numbered for north–south routes (with the lowest numbers along the Atlantic Ocean). Three-digit highways, also known as "child routes," are branches off their main one- or two-digit "parents" (for example, U.S. Route 202 is a branch of U.S. Route 2). However, US 101, rather than a "child" of US 1, is considered a "mainline" U.S. Route.
State highways are the next level in the hierarchy. Each state and territory has its own system for numbering highways, some more systematic than others. Each state also has its own design for its highway markers; the number in a circle is the default sign, but many choose a different design connected to the state, such as an outline of the state with the number inside. Many states also operate a system of county highways.
The original floating bridge was opened in 1963 as a replacement for the cross-lake ferry system that had operated since the late 19th century. In 1964, SR 520 was designated as a freeway connecting I-5 to I-405. An extension to Redmond was proposed later in the decade. In the 1970s and 1980s, sections of the freeway between Bellevue and Redmond were opened to traffic, replacing the temporary designation of SR 920. (Full article...)
The first route over the Cuyamaca Mountains was dedicated in 1912, and a plank road served as the first road across the Imperial Valley to Yuma; east of there, the Gila Trail continued east to Gila Bend. These were later replaced by U.S. Route 80 (US 80) across California and part of Arizona, and Arizona State Route 84 (SR 84) between Gila Bend and Casa Grande. The US 80 freeway through San Diego was largely complete by the time it was renumbered as I-8 in the 1964 state highway renumbering; east of San Diego, the US 80 roadway was slowly replaced by I-8 as construction progressed in the Imperial Valley. The Arizona portion of the road was built starting in the 1960s. Several controversies erupted during the construction process; questionable labor practices in Imperial County led to the federal conviction of mobster Jimmy Fratianno, and a U.S. House of Representatives subcommittee found that the Arizona government had mismanaged financial resources. (Full article...)
Interstate 196 (I-196) is an auxiliary Interstate Highway that runs for 80.6 miles (129.7 km) in the US state of Michigan. It is a state trunkline highway that links Benton Harbor, South Haven, Holland, and Grand Rapids. In Kent, Ottawa, and Allegan counties, I-196 is known as the Gerald R. Ford Freeway, or simply the Ford Freeway, after President Gerald Ford, who was raised in Grand Rapids and served Michigan in the House of Representatives for 25 years. This name generally refers only to the section between Holland and Grand Rapids. I-196 changes direction; it is signed as a north–south highway from its southern terminus to the junction with US Highway 31 (US 31) just south of Holland, and as an east–west trunkline from this point to its eastern terminus at an interchange with I-96, its parent highway. There are three business routes related to the main freeway. There are two business loops (BL I-196) and one business spur (BS I-196) that serve South Haven, Holland and the Grand Rapids areas. Another business spur for Muskegon had been designated relative to the I-196 number.
The freeway numbered I-196 is the second in the state to bear the number. Originally to be numbered as part of the I-94 corridor in the state, the Benton Harbor–Grand Rapids freeway was given the I-96 number in the 1950s while another Interstate between Muskegon and Grand Rapids was numbered I-196. That I-196 was built in the late 1950s and completed in the early 1960s. The first segment of the current I-196 was opened as I-96 near Benton Harbor in 1962. Michigan officials requested a change in 1963 which reversed the two numbers, and the subsequent segments of freeway opened northward to Holland and from Grand Rapids westward under the current number. The gap between Holland and Grandville was filled in the 1970s, and a section of freeway that runs through downtown Grand Rapids was rebuilt as a wider freeway in 2010. (Full article...)
The highway is known as National Pike because it follows the original alignment of the historic National Road. As a result, there are many historic sites along Alt US 40, including the Casselman Bridge in Grantsville and the last remaining National Road toll gate house in Maryland, located in LaVale. (Full article...)
Before I-80 was planned, the route between Council Bluffs and Davenport, which passed through Des Moines, was vital to the state. Two competing auto trails, the Great White Way and the River-to-River Road, sought to be the best path to connect three of the state's major population centers. The two trails combined in the 1920s and eventually became US Highway 32 (US 32) in 1926. US 6, which had taken the place of US 32, became the busiest highway in the state. In the early 1950s, plans were drawn up for the construction of an Iowa Turnpike, to be the first modern four-lane highway in the state, along the US 6 corridor. Plans for the turnpike were shelved when the Interstate Highway System was created in 1956. (Full article...)
The first highways along the route of the modern US 31 corridor were the West Michigan Pike, an auto trail from 1913, and later a pair of state trunklines (the original M-11 and M-58) in 1919. These state highways were redesignated US 31 on November 11, 1926, when the US Highway System was approved. Since then, the highway has been realigned in places. The highway crossed the Straits of Mackinac by ferry for about a decade in the 1920s and 1930s before the Mackinac Bridge was built, connecting to US 2 north of St. Ignace. Later, sections were converted into freeways starting in the 1950s. These segments opened through the subsequent decades with the last one opening in 2022. Future plans by the Michigan Department of Transportation (MDOT) include a bypass of Grand Haven. (Full article...)
A route along the corridor has existed since the early 20th century, as has the bridge over the San Luis Rey River near Bonsall. The route was added to the state highway system in 1933, and was officially designated by the California State Legislature as SR 76 in the 1964 state highway renumbering. The section of the highway through Oceanside and Bonsall is mostly a four-lane expressway; east of I-15, the roadway is mostly a two-lane highway. Originally, the entire highway was two lanes wide; west of Bonsall, the route was widened in stages, after decades of funding shortages, planning, and litigation. The California Department of Transportation (Caltrans) maintained plans to expand the entire length of the highway west of I-15 to an expressway, and as of May 2017, construction between Bonsall and I-15 was complete. (Full article...)
Predecessors to I-69 include the first M-29, US Highway 27 (US 27), M-78 and M-21. The freeway was not included on the original Interstate Highway System planning maps in the mid-1950s, but it was added in 1958 along a shorter route. Michigan built segments of freeway for the future Interstate in the 1960s, and the state was granted additional Interstate mileage in 1968 to extend I-69 north and east to Flint. Later extensions in 1973 and 1987 resulted in the modern highway. The first freeway segment designated as I-69 in Michigan opened in 1967, and the last was completed in 1992, finishing Michigan's Interstate System. US 27 previously ran concurrently with I-69 from the Indiana–Michigan state line north to the Lansing area, but this designation was removed in 2002. (Full article...)
Plans for a route between La Jolla and Santee date from 1959, and SR 52 was officially designated in the 1964 state highway renumbering. Construction began in 1966 at the I-5 interchange with Ardath Road leading to La Jolla. It continued with the building of San Clemente Canyon Road, which was later widened to become SR 52. The freeway was completed east to I-805 in 1970, and was built in two stages from there to Santo Road east of I-15; the last phase was completed in 1988. (Full article...)
The first section of the Creek Turnpike, from US-75 in Jenks to US-64/US-169 in Tulsa, was first authorized in 1987, with construction beginning in 1989. The turnpike's construction was controversial; homeowners along the route of the highway formed a group called Tulsans Against Turnpikes to fight the highway in both the courtroom and the media. The highway was also challenged on environmental grounds, with impacts upon wetlands and endangered species being the chief concerns. Nevertheless, the highway opened to traffic in three sections, starting from the easternmost, over the course of the first half of 1992. (Full article...)
The 40-mile (64 km) section of NY 28N not concurrent with NY 30 is designated as the Roosevelt–Marcy Trail, a scenic byway named for Theodore Roosevelt, who was then the Vice President of the United States. The byway marks the path Roosevelt took in 1901 to reach North Creek from Mount Marcy after learning that President William McKinley had been assassinated. The route has a rather scant history before its designations. The road originated as an old highway stretching from Warren County to Long Lake. It was used for transportation in the iron ore industry in Newcomb, and for the lumber industry in Minerva. New York State gained control of the road in 1909. The NY 28N designation was assigned as part of the 1930 renumbering of state highways in New York, incorporating part of pre-1930 NY 10. (Full article...)
Brockway Mountain was named for Daniel D. Brockway, one of the pioneer residents of the area. The road was constructed by the county road commission with funding through Depression-era work programs in 1933. It was briefly used as a connection for the parallel state highway after it opened. Since it opened, Brockway Mountain Drive has been recognized nationally and locally in several media outlets for its picturesque qualities, usually in profiles of Keweenaw County, the Upper Peninsula or other scenic drives. (Full article...)
Unlike most Interstate Highways, much of I-70 in Utah was not constructed parallel to or on top of an existing U.S. Route. Portions of I-70 were constructed in areas where previously there were no paved roads. Because it was built over an entirely new route, I-70 has many features that are unique in the Interstate Highway System. For example, the 110 miles (180 km) between Green River and Salina makes up the longest distance anywhere in the Interstate Highway System with no motorist services. This same piece is noted as the longest highway in the United States built over a completely new route since the Alaska Highway, and the longest piece of Interstate Highway to open at a given time. The construction of the Utah portion of I-70 is listed as one of the engineering marvels of the Interstate Highway System. (Full article...)
The United States Department of Transportation (USDOT) lists the construction of I-70 among the engineering marvels undertaken in the Interstate Highway System and cites four major accomplishments: the section through the Dakota Hogback, Eisenhower Tunnel, Vail Pass, and Glenwood Canyon. The Eisenhower Tunnel, with a maximum elevation of 11,158 feet (3,401 m) and length of 1.7 miles (2.7 km), is the longest mountain tunnel and highest point along the Interstate Highway System. The portion through Glenwood Canyon was completed on October 14, 1992. This was one of the final pieces of the Interstate Highway System to open to traffic and is one of the most expensive rural highways per mile built in the country. The Colorado Department of Transportation (CDOT) earned the 1993 Outstanding Civil Engineering Achievement Award from the American Society of Civil Engineers for the completion of I-70 through the canyon. (Full article...)
MD 170 originally served as the main highway between Baltimore and Fort George G. Meade. This highway, which included part of modern MD 174 west of Severn, was mostly constructed shortly after Camp Meade was established during World War I in the late 1910s. The Odenton–Severn portion of MD 170 was originally built as MD 554 in the 1930s, but became part of MD 170 in the mid-1940s. MD 170 went through another round of upgrades in the early 1940s due to its strategic importance during World War II. The highway originally passed through the area now occupied by BWI Airport. MD 170 was relocated north of MD 176 in the late 1940s during the construction of the airport and south of MD 176 in the late 1950s. The highway has been expanded to four lanes around its interchanges with I-195, I-695, MD 32, and MD 100 and along the perimeter of BWI Airport since the 1960s. (Full article...)
The current highway that bears the M-57 moniker is the second to do so. The first is now M-75 in the Northern Lower Peninsula. This second highway was designated in the 1930s along a different, but parallel, routing. The first major changes shifted that routing southward to the current corridor in stages. Through additional extensions and truncations, the modern routing was formed by the 1970s. (Full article...)
Route 108 is a short highway in the Bootheel of southeastern Missouri. Its eastern terminus is the Arkansas state line at Arkansas Highway 77, about six miles (10 km) south of Arbyrd, the only town on the route. Its western terminus is at U.S. Route 412 (US 412) about two miles (3 km) north of Arbyrd. Although signed as an east–west route, the route follows mostly north–south roadways. The route was designated in 1930, and was extended east in 1972. (Full article...)
M-60 is an east–west state trunkline highway in the US state of Michigan. It runs from the Niles area at a junction with US Highway 12 (US 12) to the Jackson area where it ends at Interstate 94 (I-94). The trunkline passes through a mix of farm fields and woodlands, crosses or runs along several rivers and connects several small towns of the southern area of the state. The westernmost segment runs along divided highway while the easternmost section is a full freeway bypass of Jackson.
M-60 was originally designed in 1919 with the rest of the state highway system in Michigan. It ran roughly along its current route connecting downtown Niles to downtown Jackson. In the mid-1920s, the western end was extended to New Buffalo; since then several bypasses of the smaller towns along the highway were added. One of these bypasses resulted in the creation of an alternate route (Alternate M-60, Alt. M-60) through Concord; that route has since been decommissioned. When Niles was bypassed in the 1950s, a business loop (Business M-60, Bus. M-60) was created through town. After the western end was truncated to its current location, that business loop was converted to a business spur. (Full article...)
The portion of US 13 between Delmar and Dover was constructed as a state highway during the 1920s. Between Dover and Wilmington, the route was built as part of the cross-state DuPont Highway, which was completed in 1923 and improved transportation between northern and southern Delaware. North of Wilmington, what would become US 13 was originally built as the Philadelphia Pike in the 1820s and improved to a state highway by 1920. US 13 was designated through Delaware when the U.S. Highway System was created in 1926. The route was widened into a divided highway between Dover and Wilmington in the 1930s and between Delmar and Dover in the 1950s. US 13 was routed to bypass Dover in the 1950s. In 1970, US 13 was moved to its current alignment between Wilmington and Claymont on a bypass built in the 1930s. The portion of US 13 between Dover and Wilmington saw heavy traffic heading to the Delaware Beaches in the summer, which led to the construction of a freeway "Relief Route" parallel to US 13. This freeway was built as DE 1, which was completed in 2003. The construction of DE 1 necessitated the realignment of US 13 in two places. (Full article...)
MD 355 serves as a major thoroughfare through Frederick and Montgomery counties, passing through Bethesda, Rockville, Gaithersburg, Germantown, Clarksburg, Hyattstown, Urbana, and Frederick, roughly parallel to I-270. The southern portion of the route from the Washington, D.C., border to Germantown is a suburban four- to six-lane divided highway lined with many businesses. North of Germantown, the route is predominantly a two-lane rural road until it reaches Frederick, where it passes through commercial areas in the southern part of the city. The road changes names along its route: from south to north, it is called Wisconsin Avenue, Rockville Pike, Hungerford Drive, Frederick Road, and Urbana Pike. (Full article...)
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