in a road network is an instance of
one physical road bearing two or more different highway
, or other
. When it is two freeways
that share the same right-of-way
, it is sometimes
called a common section
often use the term
-- as well as the more specific
-- to refer to
such instances although those type are the more common
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.
Often times when two routes with exit numbers overlap
(concurrency), 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 for the same route number.
Concurrencies by nation
States, highways often form concurrencies in rural
Most of the time, concurrencies are simply marked by
placing signs for both routes on the same or adjacent posts;
occasionally a state will instead sign the road as "to" the less
major route. An example of the latter is the concurrency
of Maryland Route 290 and
Maryland Route 291 in Kent County,
Maryland, where MD 290, the less major route, is signed as
"to" MD 290 along MD 291, the more major route.
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.
particularly unusual concurrency occurs along the Oklahoma–Arkansas state
At the northern end of this border Oklahoma State Highway 20
with Arkansas Highway 43
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
portions of the New York State
concur with Interstates 87
, and 190
(actually, I-84 is free except
for the one-way toll on the Beacon-Newburgh bridge over the
Hudson). Also, Interstates 70
, and 476
concur with the Pennsylvania
, and Interstate 76
concurs with a part of the Ohio
. The rest of the Ohio Turnpike is part of Interstate 80
, and much of that stretch is
also part of Interstate 90
80/90 continues as such onto the Indiana Toll Road
, with I-80 leaving that
toll road in the Chicago area and I-90 staying on it all the way to
highways are concurrent
with a non-Interstate designation in their entirety. Often times,
the reason for the Interstate ending with a simultaneous
continuation with an non-Interstate designation on a transition
from freeway to semi-freeway (expressway
or backroad/surface street.
Here is a list of examples:
Also, in some cases, two interstate highways can be concurrent.
of this is the concurrency of Interstates 20 and 59 between
west of Birmingham,
AL and west of Meridian, MS.
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
Concurrencies are also found in Canada.
Manitoba, the Trans-Canada
Highway from Winnipeg to Portage La Prairie is concurrently signed with Yellowhead Highway. In Ontario, the Queen Elizabeth
Way and Highway 403 run
concurrently between Burlington and Oakville, forming the province's only concurrency between
highways. Kings Highways
in Ontario have many concurrencies, as well as county roads that
often share concurrent termini or run concurrently for short
As highways in the United States and Canada are usually 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
example, near Wytheville, Virginia, there is a concurrency between Interstate 77 (which runs and is signed
north-south) and Interstate 81 (which
runs primarily northeast-southwest but is also signed
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 , 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.
also possesses at least three wrong-way concurrencies: an 11 km (7
mi) stretch of Saskatchewan Highways 2
and 11 between Chamberlain and Findlater, a 7 km (4 mi) stretch of British
5 and 97 in Kamloops, and a 1.5 km stretch of Highways 12 and 99 in Lillooet.
Some concurrencies have extreme examples such as triple, and even
quadruple concurrencies. Also, Interstate
25 is concurrent for US-87 for 400
miles, and runs through the entire state of Colorado.
Consolidation plans for concurrencies
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
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
M-47's current routing is not part of any of its original
Other efforts to consolidate concurrencies along with simultaneous
consolidation of route numbering involves U.S. Route 10 in
Michigan which used to multiplex with I-75/US-23 and
also multiplexed U.S. Route 24
. During that time US-10 had its terminus
scaled back to Bay City,
MI so US-10 on the Lodge
Freeway would derive into M-10 and M-4 would be deprecated as an
extension to "M-10".
Despite the consolidation overhaul,
trailblazers in the Metro Detroit
for "Route 10" still depict it as "US-10" on some
Other consolidation schemes involve the use of incorporating 2
single digit numbers into one shield, for instance U.S. Route 1/9 in
Jersey is a fairly long route which saves signage doing it
Other miscellaneous concurrencies
Other concurrencies can involve a special unnumbered tourist route
with a unique route shield being concurrent with numbered highways
in its entirety. Examples of this include Lake Superior Circle Tour
Lake Huron Circle Tour
Lake Michigan Circle Tour
and Lake Erie Circle Tour
Lake Erie's circle tour route is an exception since it is a lone
designation for the Ambassador Bridge.
All of the Great Lakes Circle Tour
a small percentage of concurrency with Interstate highways.
is the most common
example of an Interstate highway being concurrent with the routes
since all of the circle tour highways are concurrent with it.
- State Highway Routes Selected Information, 1994
with 1995 Revisions (PDF) -
see Route 3 for instance]
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