Roundabout Design
Roundabout Design
(OP)
Could somebody please tell me the percentage gradient that is allowed coming into and going away from a Roundabout.
I am working to the Irish design Guidelines.
I am working to the Irish design Guidelines.





RE: Roundabout Design
RE: Roundabout Design
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"Come to think of it, there are already a million monkeys typing on a million typewriters, and the Usenet is NOTHING like Shakespeare.
- Blair Houghton
RE: Roundabout Design
we have them in the UK and they are now throwing traffic lights at them to try and keep control of them.
they only work up to specific amount of cars and then well.
Rugged
RE: Roundabout Design
They've worked quite well in my experience though the initial prophecies were for mass confusion and accidents. We have one here in my town that has really eliminated the traffic backup that used to exist with the four way stop signs previously there (now, that was an exercise in frustration watching people try to figure out when they should go at an intersection controlled by 4 way stop signs).
RE: Roundabout Design
All intersections only work for a specific amount of cars.
Undoubtedly, the most confusing roundabout I've ever seen is at Hatton Cross, just outside Heathrow Airport. It has five legs to it, with a bus depot and tube station located between two of the legs. Where each leg of the roundabout meets the circulating lanes, there is a mini-roundabout, with traffic on the circulating lanes having to yield to inbound traffic. The circulating lanes go in both directions.
I've found a photograph. Click on it to bring up the full size. (It's approximately 250kB.)
RE: Roundabout Design
RE: Roundabout Design
I designed a few large roundabouts in my time in London, but anything with signals was analyzed in TRANSYT, an old text-based network analysis software (that has been upgraded recently, it seems), rather than traditional roundabout analysis software (ARCADY, also from the TRL family). The really big monsters sometimes go by "Gyratory", as the Hangar Lane Gyratory, which I had the joy of modeling in either TRANSYT or SATURN, I can't recall which. I also had the misfortune of trying to navigate that one in a car, but evidently I came out unscathed.
I would suggest that the biggest argument for not considering Hatton Cross's invention a roundabout would be the fact that traffic circulates in both directions.
Regardless of its classification, however, I take my hat off to the engineer who came up with that solution and had the temerity to present it to the local authority. I've been around that roundabout many times at different times of the day and I've never seen any problems with its operation!
RE: Roundabout Design
Many folks have seen an aerial photo of a new roundabout being constructed inside an old circle.
Traffic in the old circle moved at speeds up to 45 mph, with resultant chaos, including a reported crash every three to four days. Now that speeds are in the 20 mph range things are much better.
It also distinguishes them from "Seattle Circles," a sort of mutated mini-roundabout native to the Pacific Northwest.
So, in the grand American tradition of calling a spade an entrenching tool, they are roundabouts, not traffic circles.
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"Come to think of it, there are already a million monkeys typing on a million typewriters, and the Usenet is NOTHING like Shakespeare.
- Blair Houghton
RE: Roundabout Design
RE: Roundabout Design
RE: Roundabout Design
RE: Roundabout Design
RE: Roundabout Design