What is a Traffic Island?
Traffic Island is physical structure or a painted object found on roads and roadside. Traffic island serve various purposes depending it type. It is usually seen as a raised area along the road for a better & orderly flow of traffic or act as a stopping/ resting area for pedestrians. In few countries traffic islands are also referred to as channelizers as these “channelizes” the traffic plying on the road. These may be raised structures made up of concrete or a physical structure in form of boards, barricades, traffic cones etc. The terminology differs as traffic islands are also known as painted islands, ghost islands, roundabouts, refuge islands, rotary etc.
These can also be regarded as physical barriers of various shapes for channelling the traffic flow and reducing the number of conflict points. In other cases these can be painted markings just like other road markings. Their proper placement is of great importance and is a must know for a traffic engineers and urban planners as it plays an important role in transport planning. A traffic island which is much longer in length is called as traffic median. A traffic median can be a few meters long and go upto few hundreds of meters.
Example & Use of Traffic Island
The examples include roundabout, triangular traffic islands or other shape solving the required purpose. These serve an additional purpose of providing the stopping space/refuge to pedestrians, space for signage, place for fixing traffic signals and traffic light, vegetation, hawkers/vendors, space for traffic signals and sometimes of fountains or statues. They are significant as they allow easy movement of vehicles along with providing space for proper queuing of vehicles. They act as lungs for intersections as due to large number of direction change resulting in increased pressure on vehicle’s part intersections are more polluted in comparison to other part of road. So a traffic island with vegetation over it reduces the carbon footprint for that intersection.
Other use of traffic islands include slowing down the vehicles especially at the pedestrian crossings. The use of physical barriers along with the painted or rubber markings/ surface of the road is much more effective when used in combination.
Design and Geometrical Features of Traffic Islands
Since traffic island is a common name given to various road structure and markings, these can be grouped based on the use, location, size, construction type and material etc.
- Shape and size: The shape & size of traffic island is determined on the basis of function it is meant to serve. Like in case of median its much longer in length than width because its function is to divide the flow of traffic. In case of a channelizer the function of traffic island is to channelized the flow of traffic in a particular direction. These are sometimes elongated like in case of a channelizers. These can also be round like in case or rotatory and round about which are used for giving a larger manoeuvring space to drivers.
- Location: Traffic island can be present on the side of road, across the road or even in mid way along the road. The functional classification of island is the most important determining factor of the location of an island.
- Island type: The decision of using a painted, concrete structure, traffic cone etc rests with the transportation department and can be chosen as per the economics and the extent to which these fulfil the requirement. However if the traffic volume is substantial, concrete structure is generally used as it forces the user to follow it, painted lines work where people are law-abiding and the flow of traffic is relatively less.
Classification and Types of Traffic Islands
There are three main classifications involved based on the purpose they serve. The purposes served may be more than one depending on their geometry, location, size and shape.
Channelizing Island: These go by the name and functions like a channelizer which provides direction to the vehicles. The most prominent use of this type is at the turning points, these allow smooth and easy turning of traffic and prevents interference with the other straight moving vehicles. These are also found where the roads converge or diverge as they helps in reducing conflict points and allow easy merging and diverging of traffic. These can be raised or marked off area, a painted island or a pedestrian refuge.
Divisional Island: These are used along the roads. These are elongated structures which can be considered as median or divider but used for the traffic moving in the same direction. These also provide slip roads which are meant to bypass the traffic signal for straight moving vehicles. These are not meant to aid turning but helps in orderly movement of vehicles and might form a part of channelizing island which further assist in reducing conflict points. These can be placed near the road shoulder or form a part of road surfaces.
Refuge Island: These are large in size and are meant for pedestrians rather than the vehicles. These are provided to serve as a safe zones for walkers and facilitates road crossings. These are raised structures large enough for a person or a group of people to stand. These can be located on a mid section of a road at point of pedestrian crossing as these provide a safe and raised surface where driver can see them and remain alert.