Opened in 1972, the roundabout, or, to be more accurate, the collection of mini-roundabouts formally known as "County Islands", was a bold and innovative blah blah response to dealing with the problem of managing a five-way convergance of traffic on the eastern edge of town. Five mini-roundabouts radiating around a central hub allow for both clockwise and anti-clockwise movement around the whole: from the position shown to take the third exit for Gorse Hill, North Star and Elgin for example, the shortest path is permissible. By turning right at the first mini-roundabout and travelling anti-clockwise around the hub, one will not cross traffic headed for the Town Centre from Old Town on the other side. This allows for smooth handling of large traffic volumes, with congestion rarely being a problem here. Navigating the Magic Roundabout, despite being daunting for the first-timer, is a surprisingly relaxed affair, made all the more so at night by the recent upgrade from sickly sodium to Metal-Halide lighting.
Dominating the scene is a Very High mast, crowned with 12x 400W Metal-Halide lamps. This rig can be seen from some distance away, but the intrusion is mitigated to some extent by the naturalistic silver-white colour of the light. Also notable is that the installation does not appear to contribute appreciably to the [already chronic] light-pollution radiating out from the town.
The periphery is lit by 250W Metal-Halide; the light given by these is a cool blue-white, giving excellent colour-rendering and clear contrasts without appearing overly bright. Although I am informed this installation has raised illumination levels on the roundabout fourfold, this has been achieved without the unpleasant "fogging" and glare associated with HPS. Increasingly, I'm looking at how well the road-surface is illuminated under white light: the increased visual acuity is exemplified by a clear contrast of the white road-markings, which become white-on-grey, instead of orange-on-brown.
Thanks to Robert Bass; Principal Electrical Engineer at Swindon Borough Council, for technical information used in this and the preceding post.