Following Matt’s Roundabout post from this morning I thought I should share this little description of Roundabout Theory. From a fun little book called:
101 Things I Learned in Engineering School http://www.hachette.co.nz/afa.asp?idWebPage=30685&ID=682998&SID=82349443
The analysis is compelling in this abstract form, however the art comes in when choosing whether a location is appropriate for this solution as the previous post discusses.
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Dual lane roundabouts fall over when pedestrian / cycle amenity is required. Single lane works ok. The Dutch have their ‘Turbo roundabouts’ but these are intended for vehicle use only. No pedestrians or cyclists.
If you need to cater for pedestrians and cycling, and a single lane, 4 arm, roundabout (I have examples of these that cope with 12,000+ VPD) wont cope, then signalising or grade separation of the active travel routes should be considered.
A roundabout may have more capacity per lane, but in the same space you can probably fit more lanes for a standard signalised intersection than you can for a roundabout.
Quick measurement suggested that a two lane approach roundabout needs 35+ metres across, whereas a 3 lane approach traffic light needs only 20 metres.
Therefore I contest the idea that a roundabout has more capacity than a traffic light in anything more than a unconstricted environment.
Also those conflict points are misleading, as only some can realistically ever actually experience a conflict at one time depending on signal phasing.
More Dutch roundabout goodness. (Sent to me by http://bicycledutch.wordpress.com/). 11,000 VPD and good amenity for walking/cycling (off -road paths).
http://goo.gl/maps/h28cg
I used to cycle through here quite frequently:
https://maps.google.nl/maps?q=amsterdam&hl=nl&ll=52.325009,4.890895&spn=0.000649,0.004128&sll=51.492954,3.626733&sspn=0.02338,0.066047&hnear=Amsterdam,+Noord-Holland&t=h&z=19&layer=c&cbll=52.325009,4.890895&panoid=wDbCZiaPqKVtVaB0uI8dYA&cbp=11,292.58,,0,11.87
Isn’t there an intersection in Britain with roundabouts within a big roundabout?
Yes – in Swindon, Hemel Hempstead and Colchester.
http://en.wikipedia.org/wiki/Magic_Roundabout_%28Swindon%29
yeah, I’ve often wondered if the outbreaks of roundaboutism in NZ recently is the result of emigré UK traffic engineers.
That looks utterly terrifying.
I’ve been around one of these – can’t remember which – and it’s really not as bad as it looks (in a car). I don’t think they are very pedestrian of cycle friendly!
I used it for years by car and on a bike with no problem (cycling I would generally go round the least busy route, often the outside one.. the great thing is you get to choose from several options).. the story goes it was designed empirically, when computer modelling was pretty basic, with lots of cones marking out the islands and policemen on step-ladders at each entry point setting traffic off in all directions all at once in the morning rush hour, with engineers observing what happened, adjusting it overnight, until it worked.. been tweaked a few times since.
Reminds me of http://xkcd.com/253/
The first time I encountered the Hemel Hempstead Magic roundabout:
http://web.archive.org/web/20060306073755/http://www.hemelhempsteadtoday.co.uk/mk4custompages/CustomPage.aspx?PageID=4045
was at dusk in a borrowed car with fuel starvation problems and with an arm swollen up following a typhoid & cholera inoculation. It is somewhat alarming until you think of it as 6 separate roundabouts distributed around a circular 2-way road. It actually works quite well. Having a fiancee living a few miles from it meant negotiating it many times subsequently.
Example of a terrifying roundabout – Roundabout at Hutt Road and Esplanade in Petone, Lower Hutt. The City Council is currently trying to design improvements to this partly double laned roundabout on which a truck killed Superintendent Steve Fitzgerald, national manager of the Police Communications Centres in 2008 and where cars keep running into cyclists. Picture of a truck going through the site where Steve got killed here: http://tinyurl.com/mcw6gd3
yup, the Hutt Valley is badly measled with roundabouts, it’s a relief to get out of the place
I agree with Patrick, Round abouts are the best way to move traffic. No one runs a round about..well if they do they will end up with a very bent car.
On big roads where there are multi lane round abouts it would seem obvious that cyclists should either select another route, make a small detour to cross the intersection, or negotiate the round about very very carefully. I know some (many) of you will rant on about bikes should have right of way or equality with cars but grow up, thats never going to happen. You dont expect to ride your bike on the motorway so why would you expect to be riding on any road thats busy enough to have multiple lane round abouts?
Phil, cyclists are rate payers (even renters pay indirectly), and rates pay 50% of local roads. Thus THEY HAVE THE RIGHT to use these roads because the helped PAY for them! That grown up enough for you?
Hello Phil
This is one of the busiest roundabout in Hamilton, Morrinsville rd / Cambridge rd
http://www.hbn.co.nz/roundabouts.html
These guys http://www.cyclecraft.co.uk/ would love that Peter. I, on the other hand, think it is probably ok for experienced, male riders only (with perhaps the occasional female – not being sexist as stats prove this) but it is not of a standard to encourage children, inexperienced, most women, casual (as in riding style) or elderly riders.
From the Hamilton Bicycling Network website:
Our FOCUS is on ADULTS who bicycle or would like to bicycle for transport and well-being. We believe that encouraging responsible use by adults will provide a positive image for the next generation…
Hi Phil, the old “you can always go somewhere else if you don’t like it” attack, huh?
Well, these are URBAN roundabouts, mostly. So you are basically telling cyclists and pedestrians they shouldn’t be in the city? In your world, cyclists are in velodromes, and pedestrians walk in parks. What a sad life.
Glad to see that you are advocating for grade seperates cycle crossings as alternative routes for cyclists at roundabouts now Phil.
Also, if you hit me when I have right of way on my bike at a roundabout, expect to be in court.
Phil: why would you expect to be riding on any road thats busy enough to have multiple lane round abouts?
Um, maybe because it is the only practical route to where you want to go?
Er phil, you miss the point, I’m just showing the thinking behind the this typology; not advocating they’re always best. Any road design for a mix of traffic that only suits one type of user simply borders on the autistic and is a sign of technical incompetence. And where that favoured mode is the majority one it is also probably a sign of a broken and bullying process.