Signs indicating a concurrency of Interstate 93, U.S. Route 1, and Massachusetts Route 3 in Boston
A concurrency, overlap, or coincidence in a road network is an instance of one physical road bearing two or more different highway, motorway, or other route numbers.
Road enthusiasts often use the term multiplex – as well as the more specific duplex and triplex – to refer to such instances although those type are the more common instances.
Concurrency is a relatively common phenomenon: where two routes must pass through a single geological feature, or crowded city streets, it is often both economically and practically advantageous for them both to be accommodated on one road.
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Concurrencies by nation
United States
An extreme example: I-40, Business 85, US 29, US 70, US 220, and US 421 concur (run together) in Greensboro, North Carolina
In the United States, highways often form concurrencies in rural areas. Most of the time, concurrencies are simply marked by placing signs for both routes on the same post; occasionally a state will instead sign the road as “to” the less major route. Several states don’t officially have any concurrencies, instead officially ending routes on each side of one. In these states, concurrencies are typically poorly signed. In the mid-20th century, California had numerous concurrencies, but the California Legislature removed most concurrencies in a comprehensive reform of highway numbering in 1964.
The concurrent eastern and northern termini of OK-20 and AR-43 at MO-43 near Southwest City, Missouri.
A particularly unusual concurrency occurs along the Oklahoma–Arkansas state line. At the northern end of this border Oklahoma State Highway 20 concurs with Arkansas Highway 43 and the two roads run north–south along the boundary.
In some states, a concurrency can occur between an interstate highway and a state toll road. For example, much of the New Jersey Turnpike concurs with Interstate 95, and portions of the New York State Thruway concur with Interstates 87, 287, 90, 84, and 190 (actually, I-84 is free except for the one-way toll on the Beacon-Newburgh bridge over the Hudson). Also, Interstates 70, 76, and 476 concur with the Pennsylvania Turnpike, and Interstate 76 concurs with a part of the Ohio Turnpike.
Some brief concurrencies in the past have been eliminated by scaling back the terminus of a state trunkline at the route it was formerly concurrent with, and at the same time can have an upgrade of a road segment to state highway standards to replace its designation with the other one; for instance, M-47 in Michigan used to run concurrent with M-46 for only a few miles. Meanwhile a gap between M-52’s northern terminus at M-36 and M-47’s southern terminus at I-96 during the 1960s was filled in to replace much of M-47 with an extension of M-52 thereby eliminating M-47’s concurrency with M-46 in 1969. Incidentally, M-47’s current routing is not part of any of its original alignment.
United Kingdom
In the United Kingdom, it is common for major through routes to run concurrently with others. Only one road number (typically that of the more heavily used route) is ever shown on road signs however; the other road is either bracketed on the sign, implying that the major route leads to a junction with the minor route (which it will do at the end of the concurrency), or left off altogether. For example, the A82 concurs with the A85 for five miles in western Scotland. Each route-confirmation sign-header gives the road number as “A82 (A85)”. A counter-example is the concurrency of the A6 and A591 south of Kendal, where, unusually, a sign gives both roads equal status as “A591/A6″.
Canada
In Canada, it is common for a highway to carry more than one designation. In Manitoba the Trans-Canada Highway from Winnipeg to Portage La Prairie carries both Trans-Canada Highway and Yellowhead Highway signage.
Wrong-way concurrency
This westbound highway in southwestern Virginia simultaneously carries Interstates 77 and 81 in opposite directions. The “wrong-way concurrency” is also reflected in U.S. Route 52 and U.S. Route 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.
As highways in the U.S. are signed with a cardinal direction, it is possible for two highways signed with opposite, conflicting directions to be running along the same stretch of physical roadway. The road itself is likely to be actually pointed in a third direction.
For example, near Wytheville, Virginia, there is a concurrency between Interstate 77 (which runs primarily northwest-southeast but is signed north-south) and Interstate 81 (which runs primarily northeast-southwest but is also signed north-south). The road itself is oriented east-west and carries the two Interstates signed in opposite directions. So one might simultaneously be on I-77 North and I-81 South, while actually traveling due west.
At least two roads run concurrently with their own opposite direction. A short stretch of Broadway in Pawtucket, Rhode Island carries both directions of Route 114
To some extent, many traffic circles, or roundabouts, are wrong-way concurrencies. For example, if two of the roads that meet at the circle are both designated north/south then the portion of one of the roads’ southern legs will continue past the northbound entrance of the other road. At that point, the circle is heading south for the first road (ready to exit the circle), while being northerly for the other road (having just entered). However, there is never a wrong way concurrency of any one road in the circle; as an eastbound road enters a circle, that portion of the circle is eastbound for that road, bu only until the exit that continues onto that road. Continuing in the circle one immediately reaches the entrance for the westbound portion of that road, but the eastbound portion of the circle, for that road, has ended. Similarly, where there are only two roads in the circle, and the are ot both N-S or E-W, there is no wrong way concurrency at all in the circle. Based on the above, there are a great many wrong-way concurrencies sprinkled throughout the United States, though often unsigned.
References
- ^ State Highway Routes Selected Information, 1994 with 1995 Revisions (PDF) – see Route 3 for instance]
- ^ Star Tribune, Freeway flaws; Fixing them may take decades, June 3, 2005: defines “common sections” as “2 freeways share a single right-of-way”
- ^ Minnesota Department of Transportation, I-494 and I-35W Interchange Reconstruction, accessed October 2007: gives the AADT at several such interchanges, calling them “commons”
- ^ “I-279/US 19/Truck US 19/US 22/US 30 Multiplexes”. Central PA/MD roads.
External links
- Highway Multiplex Photo Gallery
Retrieved from “http://en.wikipedia.org/wiki/Concurrency_(road)”
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