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1. 1. Grade separators traffic & transportation
2. 2. Traffic problems are a bugbear in most metropolises around the world. Statistics are routinely circulated about the city worst hit by traffic congestion . However, even periodic traffic surveys and studies, as well as the imposition of regulations fail to yield appropriate solutions. In this grim scenario, the transportation engineer came upwith grade separators concept, becoming very common now. Grade separation is the process of aligning a junction of two or more transport axes at different heights (grades) so that they will not disrupt the traffic flow on other transit routes when they cross each other.  The composition of such transport axes does not have to be uniform; it can consist of a mixture of roads, footpaths, railways, canals, or airport runways. Bridges, tunnels, or a combination of both can be built at a junction to achieve the needed grade separation. INTRODUCTION
3. 3. The grade seperators are mainly divided in to two categories i.e.  OVERPASSES  UNDERPASSES OVERPASSES term used to describe the roads crossing over any other road. It can be a bridge, flyover or any other similar structure. UNDERPASSES used to describe a passage underneath something, especially a section of road that passes under another road or a railroad. An intersection formed in this way.
4. 4. GRADESEPARATOR  A grade separator can either be a flyover or an underpass, that is any structure which separates the uniform grade of a running highway into two different grades.  A bridge is a structure built to span a gorge, valley, road, railroad track, river, body of water, or any other physical obstacle, for the purpose of providing passage over the obstacle.  Grade separators can be bridges, but not all bridges are grade separators. • An example of the potential complexity of grade separation, seen in the Circle Interchange in Chicago
5. 5. Types Fullyseparated These junctions connect two roads :  Stack interchange :- two-level, three- level, or four-level stack, depending on how many levels cross at the central point  Cloverleaf interchange :- A cloverleaf interchange is a two-level interchange in which left turns (in countries that drive on the right) are handled by loop roads  Compact grade-separation:- whereby the two roads are linked by a compact "connector road", with major-minor priority junctions at each of its ends; usually a variant of the cloverleaf type interchange, but only involving two quadrants rather than four. • 4 level stack interchange between the M25 (in the foreground) and M23 in England.
6. 6. Types Partiallyseparated These junctions connect two roads, but only one is fully grade- separated, i.e. traffic on one road does not have to stop at yield lines or signals on one road, but may have to do so when switching to the other: • Diamond interchange • Parclo interchange • Single-point urban interchange • Roundabout interchange Othervariants These junctions terminate one road into another: • Trumpet interchange • Directional-T interchange
7. 7. Stack interchange • A stack interchange is a four-way interchange whereby left turns are handled by semi-directional flyover/under ramps. To go left (right in countries with left-hand drive), vehicles first turn slightly right (on a right-turn off-ramp) to exit, then complete the turn via a ramp which crosses both highways, eventually merging with the right-turn on-ramp traffic from the opposite quadrant of the interchange. • A stack interchange, then, has two pairs of left-turning ramps, of which can be stacked in various configurations above or below the two interchanging highways. • Stacks do not suffer from the problem of weaving, but require massive construction work for their flyovers. A standard stack interchange includes roads on four levels. This is not only expensive, but also creates an eyesore among local residents.
8. 8. Six-level urban stack interchange in Puxi, Shanghai, China (Nanbei Elevated Road at Yanan Middle Road) Four-level stack The High Five Interchange in Dallas, Texas, United States, is a five level interchange
9. 9. Cloverleaf interchange • A cloverleaf interchange is a two-level interchange in which left turns (in countries that drive on the right) are handled by loop roads (U.S.: ramps, UK: slip roads). • To go left (in right-hand traffic)vehicles first pass either over or under the other road, then turn right onto a one-way three-fourths loop ramp (270°) and merge onto the intersecting road. A typical cloverleaf interchange with collector/distributor roads
10. 10. Problems • A point of conflict is the merging of exiting and entering traffic in the same lane, known as weaving. • Weaving is a consequence of having too many grade separated junctions on a road in a short distance, where traffic wanting to leave the grade-separated road at the next junction has to fight for road space with traffic which has just entered from the previous one. • Weaving can be alleviated by using collector/ distributor roads to separate entering and exiting traffic. The major advantage of cloverleaf's is that they require only one bridge, which makes such junctions inexpensive as long as land is plentiful. ADVANTAGE
11. 11. Diamondinterchange • A diamond interchange is a common type of road junction, used where a freeway crosses a minor road. • The freeway itself is grade-separated from the minor road, a bridge being provided for one or the other. Approaching the interchange from either direction, an off-ramp diverges only slightly from the freeway and runs directly across the minor road, becoming an on- ramp that returns to the freeway in similar fashion. A typical diamond interchange • The Diamond interchange uses less space than most types of freeway interchange, & avoids the interweaving traffic flows that occur in interchanges such as cloverleaf.
12. 12. Thus, diamond interchanges are most effective in areas where traffic is light and a more expensive interchange type is not needed. But where traffic volumes are higher, the two intersections within the interchange, often feature additional traffic control measures such as traffic lights and extra lanes dedicated to turning traffic. Diamond interchange on I-787 in watervliet, New York
13. 13. partialcloverleaf interchange or parclo interchange • A partial cloverleaf interchange or parclo interchange is a modification of a cloverleaf interchange. It was developed by the Ministry of Transportationas a replacement for the cloverleaf on Highways, removing the dangerous weaving patterns and allowing for more acceleration and deceleration space on the freeway. • A diamond interchange has four ramps. A cloverleaf interchange has eight ramps, as does a stack interchange . A parclo is then somewhere in between, although six is the most common.
14. 14. An Autobahn Parclo Interchange variation in Germany. • Various forms of parclo interchanges are used in the Philippines' North Luzon Expressway. • The configuration of parclo interchanges (particularly those of the "folded diamond" type) allows for the consolidation of toll barriers at points where onramps and offramps run alongside each other. • A single large barrier can serve each onramp/offramp pair simultaneously, reducing construction and operation expenses.
15. 15. Single-point urban interchange • A single-point urban interchange (SPUI, pronounced also called a single- point interchange (SPI) or single-point diamond interchange (SPDI), is a type of highway interchange. The design was created in order to help move large volumes of traffic through limited amounts of space safely and efficiently. • A single point urban interchange is similar in form to a diamond interchange, but has the advantage of allowing opposing left turns to proceed simultaneously by compressing the two intersections of a diamond into one single intersection over or under the free-flowing road. Advantages • The most commonly cited advantages of single point urban interchanges are improved operation efficiency and safety as well as reduced right-of-way requirements compared to other interchange forms. • Left turning traffic from both directions of the intersecting roadways are able to turn simultaneously without crossing the path of the opposing left turns. Because traffic passing through the interchange can be controlled by a single signal. • vehicles can clear the intersection much more quickly than in a diamond interchange (which requires two sets of traffic signals).
16. 16. Disadvantages • The major disadvantage of single point urban interchanges over other types of road junctions is the increased cost due to the need for a longer or wider bridge. • A freeway-under SPUI (as in the upper diagram) requires a wider bridge over the free-flowing road to make room for the compressed on- and off- ramps. • However, this disadvantage poses less of a problem in cases where the arterial, or non-freeway road already requires a very wide bridge. A typical freeway-over SPUI.