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|Islands are often found on the approaches to roundabouts|
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An island or traffic island is a raised area in the centre of a road, usually intended as either a place to allow pedestrians to more easily cross the road; or simply to divide traffic.
Perhaps the less common of the two main uses of Islands is as a refuge for pedestrians in the middle of a busy road or junction. They come in a variety of forms, from the very simple to intricately designed areas in the middle of busy junctions. They all share some basic design features in common however. Firstly, the islands are nearly always kerbed, with drop kerbs to indicate where pedestrians are expected to cross the road. There is nearly always some form of upstanding item to alert drivers that the island is there, whether it is a bollard, railing, traffic signal or even all of these.
The simplest design is two small raised kerb islands surmounted by bollards, with the road surface passing between as the walkway. These are often additions to the road layout rather than having been included in the roads (re)design. However at busy junctions, islands can be used in the centre of turning lanes to provide 3-way provision, where all pedestrians have to make 2 crossings via the central island. Such islands are normally surrounded by railings and feature signalised crossings, often worked in with the lights for the junction. A similar design can be used to cross a busy road, where a central island provides two staggered crossings, which reduces the green-man time as pedestrians only have one carriageway to cross at a time, so increasing the traffic throughflow.
Of course, all road islands are traffic islands, but here we are considering those which are primarily designed to separate traffic, with no pedestrian consideration given. Most resemble, in general design, the simple pedestrian refuges outlined above, being a kerbed area, often surmounted by bollards or signage to provide an additional reference for drivers.
Most commonly found to segregate traffic flows at junctions, they can be triangular, rectangular or any other shape that fits the needs of the designer. Of course, there are also the large circular ones in the middle of Roundabouts, which is doubtless where some Midlanders take the word 'island' from to describe roundabouts. The islands normally split and segregate opposing traffic flows, but can also be used between lanes on approaches to junctions to force traffic into making a turn, and so prevent last minute changes of direction. In some rare instances, the islands are used between lanes, but omitted between carriageways, and instance of this can be found on the A39 Strawberry Way relief road in Wells.
Traffic Islands are also used as a form of Traffic calming. They can be commonly found on 'distributor roads' and 'relief roads' constructed in the last 20-30 years, often as small isolated islands surmounted by a single double-sided bollard. The design principle is to prevent overtaking, often even of cyclists, slow traffic down, and where there are parked cars, make traffic give way. It can be the case, however, that traffic passes on the wrong side of the bollard rather than stop and give way.