Concurrency (road)
From Wikipedia, the free encyclopedia
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.[1] When it is two freeways that share the same right-of-way, it is sometimes called a common section or commons.[2][3]
Road enthusiasts often use the term multiplex – as well as the more specific duplex and triplex – to refer to such 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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[edit] Concurrencies by nation
[edit] United States
In the United States, highways often form concurrencies in rural areas. As highways in the U.S. are signed with a cardinal direction, it is possible for two highways signed with opposite directions to be running along the same piece of road, a "wrong-way concurrency," such as Interstate 77 and Interstate 81 near Wytheville, Virginia. 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.
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 on the boundary. In its northernmost mile, the highway curves to the west, at which point OK-20/AR-43 is entirely within the State of Oklahoma.
At least two roads run concurrently with their opposite direction. A short stretch of Broadway in Pawtucket, Rhode Island carries both directions of Route 114, and a short stretch of northbound Interstate 279, as well as the ramps leading to it, in Pittsburgh, Pennsylvania carries both directions of U.S. Route 19 Truck.
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 Interstate 87, Interstate 287, Interstate 90, Interstate 84, and Interstate 190. (Actually, I-84 is free except for the one-way toll on the Beacon-Newburgh bridge over the Hudson.) Also, Interstate 70 and Interstate 76 concur with the Pennsylvania Turnpike (mostly I-76) and Interstate 76 also concurs with a part of the Ohio Turnpike.
[edit] 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".
[edit] 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.
[edit] Wrong-way concurrency
A wrong-way concurrency is a road concurrency in which at least two numbered highway routes are signed in opposite, conflicting directions on the same stretch of physical roadway.
Although each route is logically consistent with itself, wrong-way concurrency signage may lead to confusion among motorists.
The road itself is likely to be actually pointed in a third direction. For example, a north-south wrong-way concurrency would typically occur on a stretch of road that locally runs east-west; and vice versa, such as Highways 5 north and 97 south following the Trans-Canada Highway east through Kamloops, British Columbia.
This oddity is not to be confused with situations where a north-south route shares an east-west route, which is a very common occurrence. Also, there are some cases where a route's posted direction is not the same for the entire route (thus need careful consideration of apparent wrong-way concurrency), with these examples:
- Beltway situations, such as I-695 around Baltimore and I-495 around Washington, DC.
- I-69, connecting Indianapolis and Port Huron, MI; south of Lansing, Michigan it is posted as north-south and east of Lansing it is posted as east-west.
- At least part of US 1 in Connecticut has been posted as east-west, although for the rest of its route (from Canada to Key West, Florida) it is posted north-south.
[edit] 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"
