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ROAD INTERSECTIONS *3

Recap

In the previous class we discussed about

The reasons for road accidents The facilities to be provided on the road and suggest for improvementsTo collect the data for suitable Geometrical designThe measures of controlling the speed of vehicles

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* Road intersections or junctions are places where two or more roads meet or cross each other at same or different elevations. ROAD INTERSECTIONS

*1. Angle of crossing 2. Channelizing3. Entry speeds4. Camber / Gradient 5. Importance of roads 6. Pedestrian traffic 7. Visibility Factors to be considered in design of road intersections

The following are some types of road intersections

Square JunctionsAcute JunctionT-JunctionsY-JunctionsStaggered junctionsMultiple junctions*

* At-grade intersections

2. Grade separations or InterchangesTYPES OF INTERSECTIONS

C405.34* All the road intersections which meet at about the same level allowing traffic maneuvers like merging, diverging, crossing are called intersections at grade.AT-GRADE INTERSECTIONS

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C405.34*All-paved or unchannelized intersections

2. Channelized intersections

3. Roundabout or RotariesTYPES OF AT-GRADE INTERSECTIONS

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*They are paved for the whole area of roadThey are easiest to design but most complex in traffic operationsThey are lowest class of intersectionsALL-PAVED OR UN-CHANNELIZED INTERSECTIONS

C405.34 ALL-PAVED OR UNCHANNELIZED INTERSECTIONS

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C405.34* ALL-PAVED OR UNCHANNELIZED INTERSECTIONS

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C405.34*All-paved or unchannelizedIntersections

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*Channelized islands are superior to all-paved types of intersections To handle large volumes of traffic at intersection, it becomes necessary to introduce traffic islands to channalize the traffic.Traffic islands help to control speed of vehicles and angle of approach Decrease the conflict area at the intersectionsTraffic islands shall be 200mm higher than the road levelRefuse islands can be provided for pedestrians within the intersection areaCHANNELIZED INTERSECTIONS

C405.34*CHANNELIZED INTERSECTIONS

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C405.34*CHANNELIZED INTERSECTIONS

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C405.34*CHANNELIZED INTERSECTIONS

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C405.34*CHANNELIZED INTERSECTIONS

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C405.34*CHANNELIZED INTERSECTIONS

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*A rotary intersection is an enlarged road intersection where all the converging vehicles are forced to move round a large central island in one direction (clock wise) only before they can weave out of traffic flow into their respective directions.ROTARY INTERSECTION

*The main objective of rotary is to eliminate the necessity of stopping even for crossing streams of vehicles and to reduce the area of conflict.Objective

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C405.35*Rotary intersection

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C405.35*Rotary intersection

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C405.35*Rotary intersection

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There is smooth and orderly flow of traffic with minimum delay.

It provides a high degree of safety and hence there are less chances for serious accidents.

There is little loss of traffic capacity as there is continuous flow of traffic through the rotary.

A well designed rotary can handle about 390 vehicles per hour. ADVANTAGES OF ROTARY ISLAND

The wear and tear of vehicles using rotary are reduced as stopping and starting of vehicles are less frequent.

The maintenance cost is considerably reduced as the rotary is made a self-controlled traffic intersection avoiding the necessity of traffic police or signals.

Rotary islands are advantageous when the number of intersecting roads is between four and seven.

DISADVANTAGES OF ROTARIESIf traffic is to be stopped from time to time for the crossing of pedestrians.It may confuse the drivers who are not familiar with such types of constructions.It requires large area of flat land and hence, it cannot be adopted where land values are high.It proves to be unsuitable for high speed roads.There is an increase in the size of the rotary with an increase in design speed.

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REFUSE ISLANDSThese are the safety Islands having dual purpose of affording protection to the pedestrians and segregating the traffic.These are placed at 150 to 200mm above the load level.They enable pedestrians to wait while they are walking along the cross walk.

Hence, the application of the rotary is more suitable for urban and suburban conditions having relatively slow moving traffic.

C405.35*Refuse islands

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A grade separation is the arrangement of taking one road over or under another by means of a bridge. It is also known as a fly-over junction

GRADE SEPARATIONS

C405.35Clover-leaf junctions or interchanges

2. Diamond junctions or interchanges

3. Rotary interchangeTYPES OF GRADE SEPARATIONS

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C405.35 The Clover-leaf interchange avoids all the right-hand movements which are the major source of road accidents. The radius of ramps can be suitably increased to accommodate the desired volume of traffic CLOVER-LEAF INTERCHANGE

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C405.35*Clover-leaf interchange

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The diamond interchange has a wider range of applicability than any other type of interchange.It is capable of accommodating intermediate traffic volumes in rural areas where operating speeds are high and relatively large volumes in urban areas at lesser operating speeds. It is the least expensive of all interchange types The operation of the diamond interchange is highly desirable with regard to the major highway.

DIAMOND INTERCHANGE

Diamond InterchangeC405.35*

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Advantages of grade separationsIt affords the greatest road safety to vehicles at junction.It can be adopted for all likely angles and layouts of the intersecting roads.The capacity of grade separation is practically same as that of two cross roads.It grants maximum facility to the crossing traffic. It helps large value of traffic to move easily and smoothly without reducing speeds. The problems of traffic congestion during peak hours doesnt arise.There is a overall increase in comforts and convenience to the road users.