Raised platforms are one of the three methods of speed control used for COMPACT URBAN ROUNDABOUTS. Increased noise is an effect sometimes associated with platforms, but this is mainly caused by large vehicles with steel spring suspension only (which in modern fleets are increasingly being displaced by air-suspension). Noise sensitive areas such as residential housing would need special consideration for example.
The Edsel Street / Vitasovich Avenue roundabout in Henderson, Auckland, was retrofitted with new raised speed platforms with zebra crossings to facilitate better connectivity between two large shopping centres in 2011. The result is a compact roundabout that provides convenience for pedestrians and at the same time well handles the 30,000 vehicles per day. An alternative traffic signal scheme was going to cost roughly three times the cost with additional delays for both drivers and pedestrians.
Below is a two-lane roundabout in Malmo, Sweden. Although not compact designs, several of these have been built with platforms on adjoining roads to facilitate road crossings for periphery cyclist and pedestrian paths.
Below is a directional speed platform as used in Sweden and New Zealand, which has the advantage of giving passengers just the one ‘bump’. This one is asphalt which is quicker to construct, but concrete is more durable.
Below is a scheme for a three-lane compact roundabout for the Swanson Road / Universal Drive intersection in West Auckland with around 50,000 vehicles per day. It was developed as a cost-effective solution to the current two-lane roundabout which has both safety and operational issues. The only carriageway widening required is for a footpath on the north side (shown in purple hatching), meaning it can be constructed for a fraction of the price of a conventional triple-lane roundabout yet still be amenable to cyclists and pedestrians.
Below is a concept scheme for a ‘T’ junction Compact Urban Roundabout using raised platforms. Note the eastbound bypass lane, which could suffice to have a short merge area downstream since both merging vehicle streams should be at relatively low speed due to the upstream directional raised platform. The central island would be low or flush with the road surface.