There is a story that has travelled incredible distances and, perhaps more than anything else, given the unassuming Wiltshire town of Swindon cause to be discussed across the world. It's not a famous person or a particular achievement. In fact, it's far more mundane than that: it's a roundabout.
The Magic Roundabout is a fabled, almost mythical entity discussed in hushed tones by American road enthusiasts already wary of Britain's many fast, multi-lane roundabouts. Stories of it are swapped with fear and trepidation among those planning a trip to Swindon. Guide books that would otherwise have no reason to mention the place find room for a paragraph or two when this little junction is concerned.
Why? Well, because it's the roundabout that goes the wrong way, of course!
What is it?
In Swindon town centre, just next to the local football stadium, is a junction where five roads meet. Until the 1960s it was a standard roundabout - the usual British way of dealing with unusual multi-directional junctions - but even then it had traffic problems.
The most important element is, of course, that it works both ways. Because traffic can choose the shortest path between its entry and exit points, it spends less time on the junction. One of the most common movements - from Fleming Way to Queens Drive - now involves travelling about half the distance as it did when this was a conventional roundabout. And if traffic can get out more quickly, that adds up to fewer vehicles clogging up the junction at any one time.
The trade-off is that there are now a much greater number of points of conflict - places where one stream of traffic crosses another. This effect is offset by a simple priority rule on every approach to every mini-roundabout, which means that no vehicle should be held up for very long at any "give way" line. Additionally, every approach has space for several vehicles (usually three but sometimes more) to wait alongside one another: that way, when there is a gap and it's safe to move off, several vehicles can all go at the same time.
It looks like utter mayhem from the sidelines, but it's actually incredibly controlled. Traffic keeps moving almost all the time, waiting only a few seconds to join each mini-roundabout and thus steadily travelling at low speed across the junction. A normal roundabout would involve long waits to join; signals would involve bursts of movement and long enforced stoppages. As a result, it has been calculated that the Magic Roundabout has a greater throughput of traffic than anything else that it would be possible to install in the same space. Magic indeed!
How was it created?
The first Ring Junction was installed to replace an existing large roundabout in Colchester and, like the four-way design above, had a square central island. Traffic turning left or going straight ahead went around the outside as usual, and "wrong way" circulation could only be used to turn right. Really it was still a big roundabout with gaps in the central island; the RRL called them "unhooked" right turns. Unfortunately, its accident record was terrible: it proved much more dangerous than the congested roundabout it replaced, and after fiddling with road markings and signage, the experiment was abandoned, with the junction returning to its previous state.
There's a "magic roundabout" by Hatton Cross tube station in London (just inside the Southern perimeter of Heathrow Airport), and it works very well indeed. In spite of it being a major artery into the airport and having a very busy bus station adjacent to it, I've never seen it congested or clogged up (and I used it almost daily for about 15 years before moving out of the area).
Thank you for this post and the whole website - I have long been fascinated in Colchester's magic roundabouts & came here (as a member of the SABRE forum) as I saw a reference to this.
On this occasion I am prompted by comments and photographs in a Colchester reminiscence Facebook group - I am interested to read more about the development of the Colchester scheme.