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45-601: The Georgia Viaduct is a twinned bridge that acts as a flyover-like overpass in Vancouver , British Columbia, Canada. It passes between Rogers Arena and BC Place Stadium and connects Downtown Vancouver with Main Street and Strathcona . The first Georgia Street Viaduct was built between 1913 and 1915, crossing over the expanding CPR rail yards and a small portion of False Creek. The narrow structure included streetcar tracks that were never used. At one point, every second lamppost

90-722: A four-leaf clover . A cloverleaf is the minimum interchange required for a four-legged system interchange. Although they were commonplace until the 1970s, most highway departments and ministries have sought to rebuild them into more efficient and safer designs. The cloverleaf interchange was invented by Maryland engineer Arthur Hale, who filed a patent for its design on May   24, 1915. The first one in North America opened on December   15, 1929, in Woodbridge, New Jersey, connecting New Jersey Route   25 and Route   4 (now U.S. Route   1/9 and New Jersey Route   35). It

135-407: A teardrop shape, with the points facing towards the center of the interchange. Longer ramps are often required due to line-of-sight requirements at roundabouts. A partial cloverleaf interchange (often shortened to the portmanteau, parclo ) is an interchange with loops ramps in one to three quadrants, and diamond interchange ramps in any number of quadrants. The various configurations are generally

180-399: A complex appearance and are often colloquially described as Mixing Bowls , Mixmasters (for a Sunbeam Products brand of electric kitchen mixers ), or as Spaghetti Bowls or Spaghetti Junctions (being compared to boiled spaghetti ). However, they consume a significantly smaller area of land compared to a cloverleaf interchange. A combination interchange (sometimes referred to by

225-475: A directional T interchange) is typically used when a three-way interchange is required for two or three highways interchanging in semi-parallel/perpendicular directions, but it can also be used in right-angle case as well. Their connecting ramps can spur from either the right or left side of the highway, depending on the direction of travel and the angle. Directional T interchanges use flyover/underpass ramps for both connecting and mainline segments, and they require

270-412: A dumbbell interchange or a dogbone interchange, is similar to the diamond interchange, but uses a pair of roundabouts in place of intersections to join the highway ramps with the crossroad. This typically increases the efficiency of the interchange when compared to a diamond, but is only ideal in light traffic conditions. In the dogbone variation, the roundabouts do not form a complete circle, instead having

315-734: A higher, faster ramp that eventually bears left, but may be built as a right or left exit. A cloverleaf or partial cloverleaf contains some 270 degree loops, which can slow traffic and can be difficult to construct with multiple lanes. Where all such turns are replaced with flyovers (perhaps with some underpasses) only 90 degree turns are needed, and there may be four or more distinct levels of traffic. Depending upon design, traffic may flow in all directions at or near open road speeds (when not congested). For more examples, see Freeway interchange . A pedestrian overpass allows traffic to pass without affecting pedestrian safety. Railway overpasses are used to replace level crossings (at-grade crossings) as

360-661: A moderate amount of land and moderate costs since only two levels of roadway are typically used. Their name derives from their resemblance to the capital letter T, depending upon the angle from which the interchange is seen and the alignment of the roads that are interchanging. It is sometimes known as the "New England Y", as this design is often seen in the northeastern United States, particularly in Connecticut. This type of interchange features directional ramps (no loops, or weaving right to turn left) and can use multilane ramps in comparatively little space. Some designs have two ramps and

405-454: A parclo AB features a loop ramp approaching the crossroad in one direction, and beyond the crossroad in the opposing direction, as in the example image. A diverging diamond interchange (DDI) or double crossover diamond interchange (DCD) is similar to a traditional diamond interchange, except the opposing lanes on the crossroad cross each other twice, once on each side of the highway. This allows all highway entrances and exits to avoid crossing

450-581: A safer alternative. Using overpasses allows for unobstructed rail traffic to flow without conflicting with vehicular and pedestrian traffic. Rapid transit systems use complete grade separation of their rights of way to avoid traffic interference with frequent and reliable service. Railroads also use balloon loops and flying junctions instead of flat junctions , as a way to reverse direction and to avoid trains conflicting with those on other tracks. Freeway interchange Note: The descriptions of interchanges apply to countries where vehicles drive on

495-439: A safer modification of the cloverleaf design, due to a partial or complete reduction in weaving, but may require traffic lights on the lesser-travelled crossroad. Depending on the number of ramps used, they take up a moderate to large amount of land, and have varying capacity and efficiency. Parclo configurations are given names based on the location of and number of quadrants with ramps. The letter A denotes that, for traffic on

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540-543: A small angle and meet the non-freeway at almost right angles. These ramps at the non-freeway can be controlled through stop signs , traffic signals , or turn ramps. Diamond interchanges are much more economical in use of materials and land than other interchange designs, as the junction does not normally require more than one bridge to be constructed. However, their capacity is lower than other interchanges and when traffic volumes are high they can easily become congested. A double roundabout diamond interchange, also known as

585-401: A three-level semi-directional T at Highway 407 and a two-level semi-directional T at Highway 401 . Service interchanges are used between a controlled-access route and a crossroad that is not controlled-access. A full cloverleaf may be used as a system or a service interchange. A diamond interchange is an interchange involving four ramps where they enter and leave the freeway at

630-509: A three-way interchange. However, in a semi-directional T, some of the splits and merges are switched to avoid ramps to and from the passing lane , eliminating the major disadvantage of the directional T. Semi-directional T interchanges are generally safe and efficient, though they do require more land and are costlier than trumpet interchanges. Semi-directional T interchanges are built as two- or three-level junctions, with three-level interchanges typically used in urban or suburban areas where land

675-442: A toll road meets another toll road or a free highway. They are also useful when most traffic on the terminating highway is going in the same direction. The turn that is used less often would contain the slower loop ramp. Trumpet interchanges are often used instead of directional or semi-directional T or Y interchanges because they require less bridge construction but still eliminate weaving. A full Y-interchange (also known as

720-422: A traditional stack interchange. A three-level roundabout interchange features a grade-separated roundabout which handles traffic exchanging between highways. The ramps of the interchanging highways meet at a roundabout , or rotary, on a separated level above, below, or in the middle of the two highways. These interchanges can also be used to make a "linking road" to the destination for a service interchange, or

765-448: Is a bridge , road , railway or similar structure that is over another road or railway. An overpass and underpass together form a grade separation . Stack interchanges are made up of several overpasses. The world's first railroad flyover was constructed in 1843 by the London and Croydon Railway at Norwood Junction railway station to carry its atmospheric railway vehicles over

810-446: Is a 3-level stack, since the semi-directional ramps are spaced out far enough, so they do not need to cross each other at a single point as in a conventional 4-level stack. Stacks are significantly more expensive than other four-way interchanges are due to the design of the four levels; additionally, they may suffer from objections of local residents because of their height and high visual impact. Large stacks with multiple levels may have

855-428: Is an alternative four-way directional interchange. The turbine interchange requires fewer levels (usually two or three) while retaining directional ramps throughout. It features right-exit, left-turning ramps that sweep around the center of the interchange in a clockwise spiral . A full turbine interchange features a minimum of 18 overpasses, and requires more land to construct than a four-level stack interchange; however,

900-472: Is braided when at least one of the roadways reverses sides. It seeks to make left and right turns equally easy. In a pure braided interchange, each roadway has one right exit, one left exit, one right on-ramp, and one left on-ramp, and both roadways are flipped. The first pure braided interchange was built in Baltimore at Interstate 95 at Interstate 695 ; however, the interchange was reconfigured in 2008 to

945-470: Is more expensive. In a three-level semi-directional T, the two semi-directional ramps from the terminating highway cross the surviving highway at or near a single point, which requires both an overpass and underpass. In a two-level semi-directional T, the two semi-directional ramps from the terminating highway cross each other at a different point than the surviving highway, necessitating longer ramps and often one ramp having two overpasses. Highway 412 has

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990-477: The Brighton Main Line . In North American usage, a flyover is a high-level overpass, built above main overpass lanes, or a bridge built over what had been an at-grade intersection . Traffic engineers usually refer to the latter as a grade separation . A flyover may also be an extra ramp added to an existing interchange, either replacing an existing cloverleaf loop (or being built in place of one) with

1035-400: The controlled-access highway , the loop ramps are located in advance of (or approaching ) the crossroad, and thus provide an onramp to the highway. The letter B indicated that the loop ramps are beyond the crossroad, and thus provide an offramp from the highway. These letters can be used together when opposite directions of travel on the controlled-access highway are not symmetrical, thus

1080-403: The "inside" through road (on the same side as the freeway that ends) crossing each other at a three-level bridge. The directional T interchange is preferred to a trumpet interchange because a trumpet requires a loop ramp by which speeds can be reduced, but flyover ramps can handle much faster speeds. The disadvantage of the directional T is that traffic from the terminating road enters and leaves on

1125-535: The United States opened on July   7, 2009, in Springfield, Missouri , at the junction of Interstate 44 and Missouri Route 13 . A single-point urban interchange (SPUI) or single-point diamond interchange (SPDI) is a modification of a diamond interchange in which all four ramps to and from a controlled-access highway converge at a single, three-phase traffic light in the middle of an overpass or underpass. While

1170-401: The bridges are generally short in length. Coupled with reduced maintenance costs, a turbine interchange is a less costly alternative to a stack. A windmill interchange is similar to a turbine interchange, but it has much sharper turns, reducing its size and capacity. The interchange is named for its similar overhead appearance to the blades of a windmill . A variation of the windmill, called

1215-502: The compact design is safer, more efficient, and offers increased capacity—with three light phases as opposed to four in a traditional diamond, and two left turn queues on the arterial road instead of four—the significantly wider overpass or underpass structure makes them more costly than most service interchanges. Since single-point urban interchanges can exist in rural areas, such as the interchange of U.S. Route 23 with M-59 in Michigan ;

1260-537: The creation of a new basic road as a service interchange. Trumpet interchanges may be used where one highway terminates at another highway, and are named as such for to their resemblance to trumpets . They are sometimes called jug handles . These interchanges are very common on toll roads , as they concentrate all entering and exiting traffic into a single stretch of roadway, where toll plazas can be installed once to handle all traffic, especially on ticket-based tollways . A double-trumpet interchange can be found where

1305-448: The diverging windmill, increases capacity by altering the direction of traffic flow of the interchanging highways, making the connecting ramps much more direct. There also is a hybrid interchange somewhat like the diverging windmill in which left turn exits merge on the left, but it differs in that the left turn exits use left directional ramps. A braided or diverging interchange is a two-level, four-way interchange. An interchange

1350-470: The expanded freeway plan was scrapped, the replacement viaduct project proceeded. The freeways would have required demolishing buildings in neighbourhoods including Strathcona , the Downtown Eastside and Chinatown . A predominantly Black Canadian community called Hogan's Alley was bulldozed in building the viaduct. The first phase (Georgia) of the new viaduct opened to traffic on June 28, 1971, and

1395-467: The first roads to feature grade-separations. Maryland engineer Arthur Hale filed a patent for the design of a cloverleaf interchange on May   24, 1915, though the conceptual roadwork was not realised until a cloverleaf opened on December   15, 1929, in Woodbridge, New Jersey , connecting New Jersey Route 25 and Route 4 (now U.S. Route 1/9 and New Jersey Route 35 ). It

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1440-587: The opposite direction of travel and saves one signal phase of traffic lights each. The first DDIs were constructed in the French communities of Versailles ( A13 at D182), Le Perreux-sur-Marne ( A4 at N486) and Seclin ( A1 at D549), in the 1970s. Despite the fact that such interchanges already existed, the idea for the DDI was "reinvented" around 2000, inspired by the freeway-to-freeway interchange between Interstate 95 and I-695 north of Baltimore . The first DDI in

1485-508: The passing lane, so the semi-directional T interchange (see below) is preferred. The interchange of Highway 416 and Highway 417 in Ontario, constructed in the early 1990s, is one of the few directional T interchanges, as most transportation departments had switched to the semi-directional T design. As with a directional T interchange, a semi-directional T interchange uses flyover (overpass) or underpass ramps in all directions at

1530-543: The portmanteau, cloverstack ) is a hybrid of other interchange designs. It uses loop ramps to serve slower or less-occupied traffic flow , and flyover ramps to serve faster and heavier traffic flows. If local and express ways serving the same directions and each roadway is connected righthand to the interchange, extra ramps are installed. The combination interchange design is commonly used to upgrade cloverleaf interchanges to increase their capacity and eliminate weaving. Some turbine-stack hybrids: The turbine interchange

1575-467: The problem of weaving, and due to the semi-directional flyover ramps and directional ramps, they are generally safe and efficient at handling high traffic volumes in all directions. A standard stack interchange includes roads on four levels, also known as a 4-level stack, including the two perpendicular highways, and one more additional level for each pair of left-turn ramps. These ramps can be stacked (cross) in various configurations above, below, or between

1620-583: The right side of the road. For left-side driving, the layout of junctions is mirrored. Both North American (NA) and British (UK) terminology is included. The concept of the controlled-access highway developed in the 1920s and 1930s in Italy, Germany, the United States, and Canada. Initially, these roads featured at-grade intersections along their length. Interchanges were developed to provide access between these new highways and heavily-travelled surface streets. The Bronx River Parkway and Long Island Motor Parkway were

1665-455: The rightmost lane. After demerging from right-turning traffic, they complete their left turn by crossing both highways on a flyover ramp or underpass. The penultimate step is a merge with the right-turn on-ramp traffic from the opposite quadrant of the interchange. Finally, an on-ramp merges both streams of incoming traffic into the left-bound highway. As there is only one off-ramp and one on-ramp (in that respective order), stacks do not suffer from

1710-421: The road is extended. US 70 and US 17 west of New Bern, North Carolina is an example. A stack interchange is a four-way interchange whereby a semi-directional left turn and a directional right turn are both available. Usually, access to both turns is provided simultaneously by a single off-ramp. Assuming right-handed driving, to cross over incoming traffic and go left, vehicles first exit onto an off-ramp from

1755-628: The second phase (Dunsmuir) opened on Jan. 9, 1972, amid protests which attempted to block mayor Tom Campbell 's limousine from reaching the western end. The viaduct's eastbound traffic is fed from Georgia Street and leads vehicles to Prior Street and Main Street. The viaduct's westbound lanes—often referred to as Dunsmuir Viaduct because they connect to Dunsmuir Street—pass to the north of Rogers Arena. The westbound traffic comes from Prior Street and Main Street , and carries vehicles and pedestrians to Dunsmuir Street, downtown which feeds into Melville Street and eventually Pender Street. On April 5, 2015,

1800-496: The two interchanging highways. This makes them distinct from turbine interchanges, where pairs of left-turn ramps are separated but at the same level. There are some stacks that could be considered 5-level; however, these remain four-way interchanges, since the fifth level actually consists of dedicated ramps for HOV /bus lanes or frontage roads running through the interchange. The stack interchange between I-10 and I-405 in Los Angeles

1845-515: The viaduct was closed for two weeks to allow filming of the movie Deadpool , which was released on February 12, 2016. On October 27, 2015, Vancouver City Council voted to demolish the twin viaducts. A new six-lane road configuration that merges Expo and Pacific boulevards is in the planning stages. Overpass An overpass , called an overbridge or flyover (for a road only) in the United Kingdom and some other Commonwealth countries,

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1890-540: Was considered a revolutionary design at the time of its construction. A cloverleaf offers uninterrupted connections between two roads but suffers from weaving issues. Along the mainline, a loop ramp introduces traffic prior to a second loop ramp providing access to the crossroad, between which ingress and egress traffic mixes. For this reason, the cloverleaf interchange has fallen out of favour in place of combination interchanges . Some may be half cloverleaf containing ghost ramps which can be upgraded to full cloverleafs if

1935-436: Was designed by Philadelphia engineering firm Rudolph and Delano, based on a design seen in an Argentinian magazine. A system interchange connects multiple controlled-access highways, involving no at-grade signalised intersections. A cloverleaf interchange is a four-legged junction where left turns across opposing traffic are handled by non-directional loop ramps. It is named for its appearance from above, which resembles

1980-578: Was designed by Philadelphia engineering firm Rudolph and Delano based on a design seen in an Argentinian magazine. The first cloverleaf in Canada opened in 1938 at the junction of Highway 10 and what would become the Queen Elizabeth Way . The first cloverleaf outside of North America opened in Stockholm on October   15, 1935. Nicknamed Slussen , it was referred to as a "traffic carousel" and

2025-466: Was removed to reduce weight. It was replaced between 1971 and 1972 by the current viaduct, in which the two directions of traffic are structurally separated. The current Georgia Viaduct was envisioned in the early 1970s as replacing the original structure, continuing to overpass the CPR rail yards while forming part of an extensive freeway system for Vancouver. Although communities were opposed to demolition and

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