On Mon, 15 Dec 2008 12:08:54 +1100 Ian Sergeant <[email protected]> wrote:
> + When you cross this kind of roundabout when cycling, or with a > learner driver, you don't have to worry about the characteristics of > the road you are crossing (since you never turn into the traffic of > the cross road, you just cross the roundabout). This isn't just > about cyclists and learners. Its about the nature of the intersection. I'm having quite a bit of trouble understanding your point here, what difference does whether it's a node or a loop-way have on the characteristics of the side road? What difference does the size of the roundabout have to do with this? Surely you *do* turn into the traffic of the cross road, twice in fact, once for each direction, once yielding, once with right of way? Again this happens for all sizes of the roundabout. (In fact I thought that was the point of roundabouts, to reduce the points of contact to a minimum and make the laws of yielding right-of-way very clear - and to slow you down whilst doing it of course) > + It represents what is on the ground accurately. Often there is > less of an actual diversion than many other traffic calming devices, > which are not mapped. To draw it as a deviation in the road, just > isn't what is there. The only other traffic calming device I can think of that this applies to is a 'chicane', perhaps I missed a few options? Humps and their variants cause no change in the traffic flow, neither do Chokers (all listed in map features), what others are there? Given nearly all small roundabouts occupy close if not the entire road width, using the intersecting roads carriageway as part of the loop, this means the average deviation is about 1/2 a road width out and 1/2 a road width back or nearly 1 whole road width. I'm pretty sure I haven't seen a chicane deviate more than a road width (that would put you on the footpath at some point), so it's really a close call here as to whether there is '*less* of an actual diversion than *many* other traffic calming devices'. > + These have a very standardised appearance, and should be > represented in a standardised way, like a template. The benefit > isn't just in time-saving, but in identifying that all these > roundabouts are very much the same. What standard things about a suburban roundabout are there that don't equally apply to a large roundabout? The only standard things I can think of about all suburban roundabouts are: (1) They go clockwise around a central raised island (2) All approaches to the road are divided by at least a smaller splitter island (3) They have one lane (4) They have a roundabout sign displayed on all approaches Beyond this they are as varied as everything else on the planet. The only one of those that doesn't also apply to much larger roundabouts is (3) but it applies to some much larger roundabouts, so it's a bit of a non-starter. If we look at the things that vary between suburban roundabouts we find the following list: (1) The structure of the centre varies wildly beyond being raised: - some have a garden bed, some are paved, some are dirt - some are a single tier, some a 2-tiered, some are 2-tiered with the lower tier being traffic-able. (2) Some have extensive street furniture in the centre, some don't. (3) The splitter islands may or may not have signage. (4) The outer edges of the approach roads may or may not has extra curbing added to tighten the road approaches (5) The roundabouts may occupy just the existing road surfaces or may extend out beyond them, and given the variety in road widths different approaches to the same road can yield radically different judgements by people. (the extended area is often quite large on the opposite side of a 'side' road in a T-junction) (6) Not all of these are even circular, some are elliptical in shape, and of course there's the classic egg-timer shapes. (7) Quite a number of circular ones have funny offsets on opposite roads which mean your have to adjust the centre lines of the adjoining ways to make it line up (suddenly map doesn't match ground any more). 6 and 7 at least can be handled by actually drawing the roundabout as a way I guess, but then it defeats the purpose of the standardisation idea. I'd suggest in fact that suburban roundabouts don't fit any kind of template at all. <snip> the rest for now because you raise a good point about the decision order, in fact I'd even go so far as to suggest (given jackb's disagreement with me on what it means) we need to make an explicit list of what exactly defines a roundabout, I think Liz's list at the top of her PDF was a good start, plus a no-parking addition). -- =b _______________________________________________ Talk-au mailing list [email protected] http://lists.openstreetmap.org/listinfo/talk-au
