Concurrency (road)

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An extreme example: I-40, I-85 Business, US 29, US 70, US 220, and US 421 ran concurrently in Greensboro, North Carolina. US 220 and US 421 were rerouted from this concurrency in 2008, and I-85 Business was decommissioned in 2020. Greensboro road signs.jpg
An extreme example: I-40, I-85 Business, US 29, US 70, US 220, and US 421 ran concurrently in Greensboro, North Carolina. US 220 and US 421 were rerouted from this concurrency in 2008, and I-85 Business was decommissioned in 2020.

A concurrency in a road network is an instance of one physical roadway bearing two or more different route numbers. [1] When two roadways share the same right-of-way, it is sometimes called a common section or commons. [2] Other terminology for a concurrency includes overlap, [3] coincidence, [4] duplex (two concurrent routes), triplex (three concurrent routes), multiplex (any number of concurrent routes), [5] dual routing or triple routing. [6] [7]


Concurrent numbering can become very common in jurisdictions that allow it. Where multiple routes must pass between a single mountain crossing or over a bridge, or through a major city, it is often economically and practically advantageous for them all to be accommodated on a single physical roadway. In some jurisdictions, however, concurrent numbering is avoided by posting only one route number on highway signs; these routes disappear at the start of the concurrency and reappear when it ends. However, any route that becomes unsigned in the middle of the concurrency will still be signed on most maps and road atlases.


Most concurrencies are simply a combination of at least two route numbers on the same physical roadway. This is often practically advantageous as well as economically advantageous; it may be better for two route numbers to be combined into one along rivers or through mountain valleys. Some countries allow for concurrencies to occur, however, others specifically do not allow it to happen. In those nations which do permit concurrencies, it can become very common. In these countries, there are a variety of concurrences which can occur.

An example of this is the concurrency of Interstate 70 (I-70) and I-76 on the Pennsylvania Turnpike in western Pennsylvania. I-70 merges with the Pennsylvania Turnpike so the route number can ultimately continue east into Maryland; instead of having a second physical highway built to carry the route, it is combined with the Pennsylvania Turnpike and the I-76 designation. [8] A triple Interstate concurrency is found in Wisconsin along the five-mile (8.0 km) section of I-41, I-43, and I-894 in Milwaukee, Wisconsin. [9] The concurrency of I-41 and I-43 on this roadway is an example of a wrong-way concurrency.

The longest Interstate highway concurrency is I-80 and I-90 for 265 miles (426 km) across Indiana and Ohio. [10]

There are examples of eight-way concurrencies: I-465 around Indianapolis and Georgia State Route 10 Loop around downtown Athens, Georgia. Portions of the 53-mile (85 km) I-465 overlap with I-74, US Highway 31 (US 31), US 36, US 40, US 52, US 421, State Road 37 (SR 37) and SR 67—a total of eight other routes. Seven of the eight other designations overlap between exits 46 and 47 to create an eight-way concurrency. [11]

Regional examples

North America

The QEW concurrent with Highway 403 in Ontario QEW and Hwy 403 Concurrency.jpg
The QEW concurrent with Highway 403 in Ontario

In the United States, concurrencies are simply marked by placing signs for both routes on the same or adjacent posts. The federal Manual on Uniform Traffic Control Devices prescribes that when mounting these adjacent signs together that the numbers will be arranged vertically or horizontally in order of precedence. The order to be used is Interstate Highways, U.S. Highways, state highways, and finally county roads, and within each class by increasing numerical value. [12]

Several states do not officially have any concurrencies, instead officially ending routes on each side of one. [lower-alpha 1] There are several circumstances where unusual concurrencies exist along state borders. One example occurs along the OklahomaArkansas state line. At the northern end of this border Oklahoma State Highway 20 runs concurrently with Arkansas Highway 43 and the two highways run north–south along the boundary. [14]

A section of Ontario Highway 400 runs concurrent with a branch of the Trans-Canada Highway ON 400 TCH.jpg
A section of Ontario Highway 400 runs concurrent with a branch of the Trans-Canada Highway

Concurrencies are also found in Canada. British Columbia Highway 5 continues east for 12 kilometres (7.5 mi) concurrently with Highway 1 and Highway 97, through Kamloops. This stretch of road, which carries Highway 97 south and Highway 5 north on the same roadway (and vice versa), is the only wrong-way concurrency in British Columbia. Concurrencies are also very common in Quebec. Most notably, the Samuel-de-Champlain Bridge features a concurrency with three Autoroutes: A-10, A-15, and A-20. Another example is A-55, which runs concurrently with A-10, A-20, and A-40, all of which are major highways.

In Ontario, the Queen Elizabeth Way and Highway 403 run concurrently between Burlington and Oakville, forming the province's only concurrency between two 400-series highways. [15] The concurrency was not in the original plan which intended for both the QEW and Highway 403 to run parallel to each other, as the Hamilton–Brantford and Mississauga sections of Highway 403 were initially planned to be linked up along a corridor (later planned to be tolled) now occupied by Highway 407. To avoid forcing drivers to pay tolls to use a section of a continuous Highway 403, the new link was designated as a western extension of the tolled Highway 407, with the Mississauga section of Highway 403 planned to be renumbered as Highway 410. The renumbering to 410 never came to pass, [16] and consequently Highway 403 was signed concurrently along the Queen Elizabeth Way in 2002, remedying the discontinuity. Nonetheless, many surface street signs referring to that section of freeway with the QEW/Highway 403 concurrency still only use the highway's original designation of QEW, although the MTO has updated route markers on the QEW to reflect the concurrency. [17]

At the national level, the Trans-Canada Highway, which does not bear a uniform number in the eastern provinces, follows various provincial highways. In the Atlantic Provinces the main designated TCH route either follows a single numbered route across each province (an exception being the switching of the designation between Nova Scotia Highways 104 and 105), or has branches that are signed exclusively as TCH routes. In Ontario and Quebec, The TCH follows a series of provincial highways, and also has branches that follow sections of others that have concurrencies with it, signed with TCH shields alongside the provincial number.


Concurrency of the city beltway, a European road, and three first-class roads in Hradec Kralove, Czech Republic Labsky most, znacky silnic.jpg
Concurrency of the city beltway, a European road, and three first-class roads in Hradec Králové, Czech Republic
Concurrency of several cycling routes in Pisek, Czech Republic Pisek, Fugnerovo namesti a nabrezi 1. maje, znacka cyklotras.jpg
Concurrency of several cycling routes in Písek, Czech Republic

In the United Kingdom, routes do not run concurrently with others. Where this would normally occur, the roadway takes the number of only one of the routes (usually, but not always, the most important route), while the other routes are considered to have a gap and are signed in brackets (the equivalent of "to" signs in North America). An example is the meeting of the M60 and the M62 northwest of Manchester: the motorways coincide for the seven miles (11 km) between junctions 12 and 18 but the motorway between those points is only designated as the M60. European route numbers as designated by UNECE may have concurrencies (for instance E15 and E30 around Greater London), but since the E-route numbers are unsigned and unused in the UK, the existence of these concurrencies is purely theoretical.

In Sweden and Denmark, the most important highways use only the European route numbers that have cardinal directions. In Sweden the European route E6 and E20 run concurrently for 280 kilometres (170 mi). In Denmark the E47 and E55 run concurrently for 157 kilometres (98 mi). There are more shorter concurrencies. There are two stretches in Sweden and Denmark where three European routes run concurrently; these are E6, E20 and E22 in Sweden, and E20, E47, and E55 in Denmark. Along all these concurrencies, all route numbers are posted with signs. [18]

In the Czech Republic, the European route numbers are only additional, and they are always concurrent with the state route numbering, usually highways or first-class roads. In the state numbering system, concurrences exist only in first-class and second-class roads; third class roads do not have them. The local term for such concurrences is peáž (from the French word péage). In the road register, one of the roads is considered the main ("source") road and the others as the péaging (guest) roads. The official road map enables a maximum of five concurrent routes of the intrastate numbering system. [19] Cycling routes and hiking routes are often concurrent.

The Middle East

In Israel, two freeways, the Trans-Israel Highway (Highway 6), and Highway 1 run concurrently just east of Ben Shemen Interchange. The concurrency is officially designated "Daniel Interchange", providing half of the possible interchange directions. It is a one-mile (1.6 km) segment consisting of eight lanes providing high-speed access between the two highways. Access from Highway 1 west to Highway 6 south and Highway 6 north to Highway 1 east is provided via Route 431, while access between Highway 1 east to Highway 6 north and Highway 6 south to Highway 1 west are provided at Ben Shemen Interchange. The other movements are provided through the concurrency. [20]

Wrong-way concurrencies

This westbound highway in southwestern Virginia simultaneously carries I-77 and I-81 in opposite directions. The wrong-way concurrency is also reflected in US 52 and US 11, which are concurrent with I-77 and I-81, respectively. NB77SB81.JPG
This westbound highway in southwestern Virginia simultaneously carries I-77 and I-81 in opposite directions. The wrong-way concurrency is also reflected in US 52 and US 11, which are concurrent with I-77 and I-81, respectively.
An example of a wrong-way concurrency in Oklahoma City, Oklahoma; the wrong-way concurrency is highlighted in red. OKC wrongway.svg
An example of a wrong-way concurrency in Oklahoma City, Oklahoma; the wrong-way concurrency is highlighted in red.

Since highways in the United States and Canada are usually signed with assigned cardinal directions based on their primary orientation, it is possible for a stretch of roadway shared between two highways to be signed with conflicting, even opposite, cardinal directions in a wrong-way concurrency. For example, near Wytheville, Virginia, there is a concurrency between I-77 (which runs primarily north–south, as it is signed) and Interstate 81 (which runs primarily northeast–southwest, but is also signed north–south). Because of the way they intersect, the section of Interstate where they overlap has the two roads signed for opposite directions, leading to the town's nickname of "Which-Way-Ville". [21] One might simultaneously be on I-77 northbound and I-81 southbound, while actually traveling due westbound. [22] An unusual example of a three-directional concurrency occurs southeast of Rhinelander, Wisconsin, where US 8 westbound (the actual compass direction) converges with southbound Wisconsin Highway 17 and northbound Wisconsin Highway 47.

Effect on exit numbers

Often when two routes with exit numbers overlap, one of the routes has its exit numbers dominate over the other and can sometimes result in having two exits of the same number, albeit far from each other along the same highway. An example of this is from the concurrency of I-94 and US 127 near Jackson, Michigan. The concurrent section of freeway has an exit with M-106, which is numbered exit 139 using I-94's mileage-based numbers. US 127 also has another exit 139 with the southern end of the US 127 business loop in Mount Pleasant, Michigan. (US 127's mile markers in Michigan reflect the cumulative distance north of the Ohio state line; the numbers resume north of the I-94 overlap and reflect the distance accumulated on that concurrency.) [23]

However, there are also instances where the dominant exit number range is far more than the secondary route's highest exit number, for example the concurrency of I-75 and I-85 in Atlanta, Georgia — where I-75 is dominant — the exit numbers range from 242 to 251, while I-85's highest independent mile marker in Georgia is 179. [24]

Consolidation plans

US 1/9 concurrency signed on one shield NJ guide sign.jpg
US 1/9 concurrency signed on one shield

Some brief concurrencies in the past have been eliminated by reassigning the designations along the roadways. This can involve scaling back the terminus of one designation to the end of a concurrent section. At the same time, there could be an extension of another highway designation that is used to replace the newly shortened designation with another one.

Between states, US 27 in Michigan previously ran concurrently with I-69 from the Michigan–Indiana state line to the Lansing, Michigan, area. From there it turned northwards to its terminus at Grayling. In 1999, the Michigan and Indiana departments of transportation petitioned the American Association of State Highway and Transportation Officials for permission to truncate US 27 at Fort Wayne, Indiana. [25] In 2002, Michigan removed the US 27 designation from I-69 and extended the US 127 designation from Lansing to Grayling. [26] MDOT's stated reason for the modification was to "reduce confusion along the US 27/US 127 corridor". [27] After US 27's signage was removed, the highway north of the Lansing area was renumbered US 127, and the US 27 designation was removed from I-69. [27]

Some consolidation schemes involve the use of incorporating two single-digit numbers onto one marker, as along the US 1/9 concurrency in northern New Jersey. [28] In the mid-20th century, California had numerous concurrencies, but the California Legislature removed most of them in a comprehensive reform of highway numbering in 1964. [29]

See also


  1. Arkansas's highways exist in many officially designated "sections" rather than form concurrencies. Arkansas Highway 131 exists in five sections as an example. [13]

Related Research Articles

US Route 223 or US Highway 223 (US 223) is a diagonal (northwest–southeast) United States Numbered Highway lying in the states of Michigan and Ohio. The southernmost section is completely concurrent with the US 23 freeway, including all of the Ohio segment. It connects US 23 in the south near Toledo, Ohio, with US 127 south of Jackson, Michigan. The highway passes through farmland in southern Michigan and woodland in the Irish Hills. Including the concurrency on the southern end, US 223 is 46.34 miles (74.58 km) in total length.

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 together. In Kent, Ottawa, and Allegan counties, I-196 is known as the Gerald R. Ford Freeway, or simply the Ford Freeway, after the 38th President of the United States, Gerald Ford, who was raised in Grand Rapids and served Michigan in the House of Representatives. 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 currently three business routes related to the main freeway. There are two business loops and one business spur that serve South Haven, Holland and the Grand Rapids areas. Another business spur for Muskegon had been designated relative to the I-196 number.

M-79 is an east–west state trunkline highway in the central portion of Lower Peninsula of the U.S. state of Michigan. The western terminus is about three miles (4.8 km) southeast of Hastings at the junction with M-37 and the eastern terminus is in downtown Charlotte at the junction with M-50 and Business Loop Interstate 69 (BL I-69). It passes through Quimby and Nashville, where there is a junction with M-66. The entire highway is undivided surface road. It has no direct access with Interstate 69 (I-69), although a sign for the highway is located on southbound I-69 at exit 61.

M-50 is a state trunkline highway in the US state of Michigan. Although designated as an east–west highway, it is nearly a diagonal northwest–southeast route. The western terminus is at exit 52 along Interstate 96 (I-96) near Alto a few miles east of the metro Grand Rapids area, and its eastern terminus is in downtown Monroe at US Highway 24. In between the trunkline runs through seven counties of the southern part of the Lower Peninsula mostly through rural farm fields and small communities. The highway also runs through downtown Jackson to connect between two freeway sections of US 127. In the Irish Hills area of the state southeast of Jackson, M-50 runs next to Michigan International Speedway.

M-51 is a north–south state trunkline highway in the southwestern portion of the US state of Michigan. The southern terminus is at a connection with State Road 933 across the Michigan–Indiana state line near South Bend, Indiana. From there the trunkline runs north through an interchange with US Highway 12 (US 12) into Niles along a route that was once part of Business US 12. North of Niles, the highway runs parallel to a river and a rail line through rural areas. The northern terminus is on Interstate 94 (I-94) west of Paw Paw.

M-247 is a north–south state trunkline highway in the US state of Michigan, connecting M-13 to the Bay City Recreation Area, entirely within Bangor Township. As a state trunkline, M-247 runs north from M-13 before turning to access the park, a distance of 3.036 miles (4.886 km). The highway carries just over 6,000 vehicles a day on average. The roadway has been part of the state trunkline highway system since the 1920s, and from 1961 until 1998, it was the highest non-Interstate highway in the state. Before it was given the M-247 designation, the roadway has been a part of M-111 and M-47.

M-57 is an east–west state trunkline highway in the US state of Michigan. The 105.377-mile (169.588 km) highway connects US Highway 131 (US 131) near Rockford on the west end to M-15 near Otisville in the Lower Peninsula. In between, the mostly rural highway passes through farmland and connects several highways and smaller towns together. Three of these highways are freeways: US 131, US 127 and Interstate 75 (I-75). Along the way, between 3,700 and 22,300 vehicles use the highway daily.

US Highway 27 (US 27) is a part of the US Highway System that now runs from Miami, Florida, to Fort Wayne, Indiana. In the US state of Michigan, it was a north–south state trunkline highway that entered the state south of Kinderhook and ended south of Grayling. Its route consisted of a freeway concurrency with Interstate 69 (I-69) from the state line north to the Lansing area before it followed its own freeway facility northward to St. Johns. From there north to Ithaca, US 27 was an expressway before continuing as a freeway to a terminus south of Grayling.

US Highway 24 is a United States Numbered Highway that runs from Minturn, Colorado, to Independence Township, Michigan. In Michigan, it is also known as Telegraph Road and runs for 79.828 miles (128.471 km) as a major north–south state trunkline highway from Bedford Township at the Ohio state line through Metro Detroit. The highway runs through three counties in southeastern Michigan, Monroe, Wayne and Oakland, as it parallels the Lake Erie shoreline and bypasses Metro Detroit on the west. Telegraph Road connects several suburbs together and passes through the western edge of Detroit before it terminates northwest of Clarkston at an interchange with Interstate 75 (I-75).

M-199 is a state trunkline highway near Albion in the US state of Michigan. The western terminus of the 4.030-mile-long (6.486 km) road is in Sheridan Township at exit 119 off Interstate 94 (I-94). The eastern terminus is a junction with Business Loop I-94 downtown Albion. The entire road is within Calhoun County and runs through rural farm fields outside of Albion; in town it is a residential street. The M-199 designation had previously been applied to a highway in the Upper Peninsula in the 1930s. The current highway was previously part of other highways in the first half of the 20th century before it was transferred to local control around 1960. It was later transferred back to state control in 1998 and remains unchanged since.

M-36 is a state trunkline highway in the Lower Peninsula of the US state of Michigan that runs in a west–east direction from Mason to Whitmore Lake. The trunkline connects US Highway 127 (US 127) south of Lansing and US 23 north of Ann Arbor. The highway connects several smaller communities in the rural areas along its route. M-36 also runs concurrently with two other roadways, sharing pavement with M-52 and County Road D-19. According to traffic surveys in 2010, between 650 and 15,300 vehicles used the highway on average each day.

M-68 is an east–west state trunkline highway located in the northern part of the Lower Peninsula of the US state of Michigan. The western terminus of the highway begins four miles (6.4 km) east of the Little Traverse Bay of Lake Michigan and ends a few blocks from Lake Huron in Rogers City. M-68 skirts just south of Indian River and Burt Lake.

M-83 is a north–south state trunkline highway in the Lower Peninsula of the US state of Michigan primarily serving as a link between Interstate 75/US Highway 23 (I-75/US 23) in Birch Run, including a short east–west section with M-54, and the Bavarian-themed town of Frankenmuth. M-83 is primarily a north–south trunkline that passes by such landmarks as Bronner's Christmas Wonderland, Zehnder's and the Bavarian Inn before leaving town. The landscape in the remainder of the area is composed of farm fields between Frankenmuth and the northern terminus at M-15 near Richville.

M-106 is a state trunkline highway in the Lower Peninsula of the US state of Michigan in and near the city of Jackson. M-106 travels in a southwest-to-northeast direction from Jackson to Gregory at a junction with M-36 just a few miles northwest of Hell. The highway was first designated in 1928 running north out of downtown Jackson. It connected U.S. Highway 12 (US 12) to the state prison and Bunkerhill Road. A pair of changes in the early 1930s resulted in the extension eastward to Gregory. From the 1960s until the early years of the 21st century, a section of M-106 in downtown Jackson was routed along one-way streets.

US Highway 12 (US 12) is an east–west US Highway that runs from Aberdeen, Washington, to Detroit, Michigan. In Michigan it runs for 210 miles (338 km) between New Buffalo and Detroit as a state trunkline highway and Pure Michigan Byway. On its western end, the highway is mostly a two-lane road that runs through the southern tier of counties roughly parallel to the Indiana state line. It forms part of the Niles Bypass, a four-lane expressway south of Niles in the southwestern part of the state, and it runs concurrently with the Interstate 94 (I-94) freeway around the south side of Ypsilanti in the southeastern. In between Coldwater and the Ann Arbor area, the highway angles northeasterly and passes the Michigan International Speedway. East of Ypsilanti, US 12 follows a divided highway routing on Michigan Avenue into Detroit, where it terminates at an intersection with Cass Avenue.

Interstate 69 (I-69) is a part of the Interstate Highway System that will eventually run from the Mexican border in Texas to the Canadian border at Port Huron, Michigan. In Michigan, it is a state trunkline highway that enters the state south of Coldwater and passes the cities of Lansing and Flint in the Lower Peninsula. A north–south freeway from the Indiana–Michigan border to the Lansing area, it changes direction to east–west after running concurrently with I-96. The freeway continues to Port Huron before terminating in the middle of the twin-span Blue Water Bridge while running concurrently with I-94 at the border. There are four related business loops for I-69 in the state, connecting the freeway to adjacent cities.

There are currently eight business routes of Interstate 94 (I-94) in the US state of Michigan. These business routes connect I-94 to the downtown business districts of neighboring cities. Seven of the eight routes are business loops which bear the Business Loop I-94 designation while one is a business spur that bears the Business Spur I-94. These loops are former routings of I-94's two predecessors in Michigan: US Highway 12 (US 12) or US 25. The westernmost BL I-94 runs through the twin cities of Benton Harbor and St. Joseph along the former routing of US 12 and US 31/US 33 that now includes a section of the Lake Michigan Circle Tour in the state. The loops in Kalamazoo, Battle Creek, Marshall, Albion, and Jackson were also formerly segments of US 12 which were later designated as separate version of Business US Highway 12 through their respective cities before becoming BL I-94s in 1960. The BL I-94 in Kalamazoo was converted into BS I-94 in 2019. The route of the business loop through Ann Arbor was previously US 12 and then later M-14 before receiving its current moniker. The BL I-94 through Port Huron was previously US 25 and then Business US Highway 25.

US Highway 10 (US 10) is a part of the United States Numbered Highway System that runs from West Fargo, North Dakota, to the Lower Peninsula of the US state of Michigan. The highway enters Michigan on the SS Badger, which crosses Lake Michigan between Manitowoc, Wisconsin, and Ludington. As the highway crosses the state, it is a two-lane undivided highway between Ludington and Farwell and a freeway from Farwell east to the highway's terminus in Bay City. US 10 runs concurrently with US 127 in the Clare area along a section of freeway that includes a welcome center in the median. Outside of the Clare and Midland areas, US 10 runs through rural areas of Western and Central Michigan in a section of the Manistee National Forest as well as farm fields.

Michigan State Trunkline Highway System Highway system in Michigan

The State Trunkline Highway System consists of all the state highways in Michigan, including those designated as Interstate, United States Numbered, or State Trunkline highways. In their abbreviated format, these classifications are applied to highway numbers with an I-, US, or M- prefix, respectively. The system is maintained by the Michigan Department of Transportation (MDOT) and comprises 9,669 miles (15,561 km) of trunklines in all 83 counties of the state on both the Upper and Lower peninsulas, which are linked by the Mackinac Bridge. Components of the system range in scale from 10-lane urban freeways with local-express lanes to two-lane rural undivided highways to a non-motorized highway on Mackinac Island where cars are forbidden. The longest highway is nearly 400 miles (640 km) long, while the shortest is about three-quarters of a mile. Some roads are unsigned highways, lacking signage to indicate their maintenance by MDOT; these may be remnants of highways that are still under state control whose designations were decommissioned or roadway segments left over from realignment projects.


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