Развязки типа «полный клевер» и их особенности

A type of freeway interchange

A directional interchange, colloquially known as a stack interchange, is a type of grade separated junction between two controlled access highways that allows for free flowing movement to and from all directions of traffic. These interchanges eliminate the problems of weaving, have the highest vehicle capacity, and vehicles travel shorter distances when compared to different types of interchanges. The first directional interchange built in the world was the Four Level Interchange which opened to Los Angeles traffic in 1949.

A directional interchange is a grade separated junction between two roads where all turns that require crossing over or under the opposite road's lanes of travel to complete the turn utilize ramps that make a direct or semi direct connection. The difference between direct and semi direct connections is how much the motorist deviates from the intended direction of travel while on the ramp. Direct ramps are shorter and can handle higher traveling speeds than semi direct.

The four level stack (or simply four stack) has one major freeway crossing another freeway with a viaduct, with connector flyover ramps crossing on two further levels. This type of interchange does not usually permit U turns. 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).

The initial design of Highway 407 had several four level stack interchanges planned at junctions with existing 400 series highways, but ending up only one example was built—the interchange at Highway 400 in Vaughan, Ontario, which is also the only true four level stack in all of Canada. Highway 407's other proposed four level stacks at Highway 410 and Highway 404 were reduced to three level cloverstack interchanges with loop ramps instead of a fourth level of semi directional ramps. Similarly the Highway 407 interchange with Highway 427 has four levels but only two semi directional flyover ramps (that cross each other) connecting to Highway 427 south of that junction, while two loop ramps link Highway 407 with Highway 427 north of that junction.

In Belgium, on the Brussels Ring there are four level stack interchanges: The Grand Bigard and Machelen interchange (only partly in use). In Germany, there is one, the Wetzlarer Kreuz. In Greece, there is also four stack interchange near Metamorfosi, which connects the A1 Highway with Attiki Odos. In the Netherlands there is currently four level stack interchange: the Prins Clausplein near The Hague. It forms the junction of the A4 and A12. In the United Kingdom there are four level stacks: at the junction of the M4 and M25 near Heathrow Airport in London (the Thorney Interchange), at the junction of the M23 and M25 to the south of London (the Merstham Interchange), and at the junction of the M4 and M5 near Bristol (the Almondsbury Interchange). 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 (a north–south road at this junction) is offset to the east by approximately 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 A66.

The Light Horse Interchange at the junction of the M4 and M7 is a four level stack interchange in Sydney, New South Wales, Australia. Opened in late 2005, it is the largest in the Southern Hemisphere. The EB Cloete Interchange just outside Durban, South Africa, is another four level stack interchange. The N3 is the busiest highway in South Africa and a very busy truck route. Because Johannesburg is not located near a body of water, most of the city's exports travel through the Port of Durban. The N2 connects Cape Town with Durban and serves the South African cities of Port Elizabeth, East London and George and the towns of Grahamstown, Port Shepstone, Richards Bay and the iSimangaliso Wetland Park. Two busy roads intersect at the junction. A four level stack interchange was chosen to serve the high volumes of traffic.

In Texas, many stacks contain five levels. They usually have the same configuration as four level stacks, but frontage roads add a fifth level. The frontage roads usually intersect with traffic lights and are similar to a grid of nearby one way streets. A common setup is for one mainline to go below grade and another to go above grade. The intersection of the frontage roads is typically at grade or close to it. Two pairs of left turn connectors are built above these. The Dallas–Fort Worth metroplex has several five level stacks, most notably the High Five Interchange between US 75 and I 635; completed in 2005 and currently the tallest interchange in the world. Others can be found at the interchanges between State Highway 121 (SH 121) and the Dallas North Tollway, SH 121 and I 35E/US 77, I 30 and I 35W, I 30 and President George Bush Turnpike and others which are technically five levels but do not fit under a Texas style stack configuration (i. e. the extra level being located away from the central stack or existing in only one direction). The Houston area has seven five level stack interchanges along Beltway 8: at I 10 east and west of downtown, I 69 northeast and southwest of downtown, I 45 north and south of downtown, and US 290 in the beltway's northwest quadrant. The newly reconstructed interchange of I 610 and I 69, 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. Though not a Texas style stack in the above sense, an unusual stack is nonetheless found in Houston that features more than four levels of traffic but whose fifth level exists in only one direction. In 2011, the previously four level stack interchange between I 610 and I 10 on the city's east side gained a new (though long planned) level of complexity with the opening of four ramps connecting the new US 90 (Crosby Freeway) to the east, featuring direct movements for the new freeway to and from the southeast quadrant of I 610, to westbound I 10, and from eastbound I 10. It is the latter ramp which gives the interchange the fifth level, as US 90 to I 10 westbound merges onto I 10 before crossing I 610. (None of the frontage roads for these highways cross the interchange itself, and thus do not factor into the complexity of the stack.) More than 40 bridges make up the five level stack interchange known as the Big I between I 40 and I 25 in Albuquerque, New Mexico. China is also home to many Texas style stack interchanges. For example the Nanjing's Yingtian Street Elevated has one each where it intersects the Inner Ring Road twice.

Sometimes a fifth level is added for HOV connectors. An example of this exists in Los Angeles, California, at the Judge Harry Pregerson Interchange. The connector from HOV southbound 110 to HOV westbound 105 can be at the same level as the connector from mixed eastbound 105 to mixed northbound 110, but the connector from HOV southbound 110 to HOV eastbound 105 needs to be higher level, since it crosses over the former connector. Another case is where connection to nearby arterials suggests that another level may be useful, thus making the interchange more complicated but easier to use. In the Atlanta area, a side ramp forms the fifth level of the Tom Moreland Interchange, colloquially known as Spaghetti Junction, found in DeKalb County, Georgia.

There is a six level stack on the Yan'an East Road Interchange in Puxi, Shanghai, with no dedicated HOV/bus/truck lanes. It is six level stack because it is formed by two elevated highways, Nanbei Elevated Road and Yan'an Elevated Road with service roads and a footbridge underneath. The centrally located interchange has a central pillar known as the Nine Dragon Pillar The story is that after several construction accidents, a monk suggested the nine dragon be welcomed with a bas relief sculpture depicting the dragon. An unusual six level stack is located at the junction between Interstate 35E and I 635 in Dallas, Texas, and does not contain any service or frontage roads. The interchange features two levels of highway with the top three levels consisting of direct connection ramps and HOV connectors. A single ramp leading from I 635 westbound to I 35E southbound weaves underneath the I 635 eastbound bridge, making the interchange six levels. The interchange between I 35E and the Sam Rayburn Tollway in Lewisville, Texas, although similar in design to five level stacks elsewhere in Texas, also qualifies as a six level stack, since the ramp connecting the eastbound Sam Rayburn Tollway with northbound I 35E goes over the fifth level ramps connecting I 35E in both directions with the Sam Rayburn Tollway. The ramp connecting the westbound Sam Rayburn Tollway with southbound I 35E is on the fourth level of the interchange, going under the fifth level ramps connecting both directions of I 35E with the Sam Rayburn Tollway.