interchange is a free-flowing grade separated junction
between two or more roads that
allows turning in all directions. A stack interchange has the
highest vehicle capacity among different types of interchanges.
Stack interchanges are most expensive, both in terms of land and
construction costs, and can be subject to closure during icy
The four-level stack (or simply four-stack
) has one major
road crossing another on a bridge, with connector roads crossing on
two further levels. This type of interchange does not usually
. Interestingly, the four-level
stack creates two "inverse" dual-carriageways—the turn ramps
crossing the middle section have traffic driving on the opposite
side of oncoming traffic to usual (see diagram for clarity).
stack interchange in the world was the aptly-named Four Level
Interchange (renamed the Bill Keene Memorial Interchange),
built in Los Angeles,
California, at the junction of U.S. Route 101
and State Route 110
. Since then, Caltrans has built eight more four-level stacks
throughout the state of California, as well as a larger number of three-level variants
(where the least-used left-turning ramp is built as a
cloverleaf-like 270-degree loop to save money).
One of the
first four-level stack interchanges was constructed over Interstate 84 in Farmington,
Connecticut, for the controversial Interstate 291 beltway around
the city of Hartford.
Most of the I-291 beltway was later
cancelled, and the sprawling stack lay dormant for almost
twenty-five years. In 1992, the extension of Connecticut
Route 9 to Interstate 84 utilized the I-291 right-of-way
and some sections of the abandoned interchange.
ramps still remain unused, including abandoned roadbed for
Interstate 291 both north and south of the complex.
four-level stack is used for the interchange between Interstate 90 and Interstate 405 in Bellevue,
planned to build many four-level stack interchanges, the Canadian province of
Ontario has only one true four-level stack interchange—the
interchange between Highway
400 and Highway
Planned four-level stacks at Highway 407
and Highway 410
, and Highway 407
and Highway 404
were reduced to
three-level interchanges. The interchange between Highway 401
, and 410
is almost a full four level stack,
with a loop ramp planned to be added in the northeast quadrant.
There are plans for a four-level stack to be built at Conestoga Parkway
Kingdom there are three four-level stacks: at the junction
of the M4 and M25 near
Airport in London, at the
junction of the M23 and M25 to the south of London, and at the junction of the
M4 and M5
near Bristol (the
The M4/M25 junction is particularly
unusual as it also has a railway line bisecting it at its lowest
level. The M4/M25 junction is slightly offset so there is no point
where all four levels are directly above each other. M25
(north-south road in this junction) is offset to the east by
approximately 60 metres (200 feet). The junction of the A19 and A66 in Teesside uses a three-level variant, with a 270-degree loop
allowing southbound A19 traffic to exit to the westbound
Lighthorse Interchange at the junction of the M4 and M7, is
an example of a four-level stack interchange in Sydney, New South
EB Cloete Interchange just
outside of Durban,
South Africa is another example of a four-level stack
the busiest highway in South Africa and is a very busy truck route.
Johannesburg is not located near a body of water, most of the
city's exports travel through the Port of Durban.
N2 connects Cape Town with Durban, and it
serves the South African cities of Port Elizabeth, Plettenberg Bay, Margate, and Greater St. Lucia Wetland Park.
busy roads intersect at the junction. A four-level stack
interchange was chosen to serve the high volumes of traffic.
In Texas, five-level stacks typically have the same configuration
as four-level stacks, with frontage
constituting the fifth level, often near grade. Frontage roads
usually intersect with traffic
lights, and are similar to a grid of nearby one-way streets.
Texas, area has 5 five-level stack interchanges along
Beltway 8: at Interstate 45 north of downtown, U.S. Highway
, Interstate 10
downtown, U.S. Highway 59
southwest of downtown, and Interstate 45
southeast of downtown. The
newly-reconstructed interchange of Interstate 610
and U.S. 59
, with the
new I-610 northbound feeder road built underground and the new
I-610 southbound feeder road overpass, is also a five-level stack
interchange. In Dallas, the award-winning High Five
Interchange was completed in 2005 and features some ramps which
are more than 12 stories above the
An alternative configuration of a five-level stack exists for
intersections. An example of this configuration exists in
California, at the Judge Harry
Pregerson Interchange of Interstate 110 and Interstate 105; the interchange
has a normal four-level configuration plus a fifth level for
HOV-only traffic to transition from either direction on I-105 to
I-110 northbound and from I-110 southbound to either direction on
This configuration allows these HOVs to avoid the
congested general use lanes and ramps, particularly on Interstate
Atlanta area, a side ramp forms the fifth level of the Tom Moreland
Interchange in DeKalb County, Georgia.
- TexasFreeway > Houston > Photo Gallery > Beltway
- Interstate 610 at U.S. 59 in Houston, Texas.
Google Maps. Last accessed November 19, 2006.