Module 6 : Traffic Intersection Control

Lecture 33 : Grade Separated Intersection

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	Classification of Grade Separated Intersection One of the distinctions made in type of interchange is between the directional and the non directional interchange. Directional interchanges are those having ramps that tend to follow the natural direction of movement. Non directional interchanges require a change in the natural path of traffic flow. A comprehensive classification plan for grade separated intersection design which includes all possible geometric patterns has not yet been developed. The design and operational characteristics of each of the major interchange types are mentioned as follows and are discussed in the following sections. Underpass Overpass Trumpet Interchange Diamond Interchange Cloverleaf Interchange Partial Cloverleaf Interchange Directional Interchange Bridged Rotary Underpass An underpass or a tunnel is an underground passageway, completely enclosed except for openings for ingress and egress, commonly at each end. A tunnel may be for foot or vehicular road traffic, for rail traffic. If an underpass is constructed for pedestrians and/or cyclists beneath a road or railway, allowing them to reach the other side in safety, then such a construction is termed as a Subway. These are constructed when it is necessary for pedestrians to cross a railroad or a limited-access highway. Subways may also be constructed for the benefit of wildlife Overpass An overpass also known as a flyover, is a bridge, road, railway or similar structure that crosses over another road or railway. A pedestrian overpass allows pedestrians safe crossing over busy roads without impacting traffic. And Railway overpasses are used to replace at-grade crossing as a safer alternative. Overpasses allows for unobstructed rail traffic flow from mixing with vehicular and pedestrian traffic. Stack interchanges are made up of many overpasses. Trumpet Interchange Trumpet interchanges have been used where one highway terminates at another highway. These involve at least one loop ramp connecting traffic either entering or leaving the terminating expressway with the far lanes of the continuous highway. These interchanges are useful for highways as well as toll roads, as they concentrate all entering and exiting traffic into a single stretch of roadway, where toll booths can be installed. Trumpets are suitable at the locations where the side road exists on only one side of the freeway, and traffic is relatively low. Each entrance and exit consists of acceleration or deceleration lanes at each end. It requires only one bridge and is the most traditional way of grade separating a three way junction. The principal advantages are low construction cost and are useful for highways as well as toll roads. But the limitations in employing trumpet interchanges are it leaves a redundant patch of the land within the loop, Disorienting to navigate for those driving in the direction that uses the loop. Moreover scaling down the interchange often results in a more dangerous suffers congestion from articulated lorries that have tipped over.