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I'm mapping some ways in town which in places have physical and marked barriers between carriageways plus turning lanes, and multiple forward lanes. In other places they're simple roads with one lane in either direction and just a dotted line separating oncoming traffic. I realise there's a need to keep things simple, but there's also a need to map complex lanes and barriers accurately. At what point should one decide to map a partly-dualled carriageway using two ways rather than one? I'm trying to apply some vague criteria to keep my mapping from descending into a pit of insane detail, and I've discussed it on the local mailing list and in IRC without much in the way of resolution. Does:
seem sound, or does it err on the side of too much dividedness? If the latter, where should the cutoff lie?
This question is marked "community wiki".
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There are some occasions where a non-divided highway is divided for the sake of safety for a - relatively - short way. E.g. here the 2+2 lane highway (under the bridge) is divided along a bend for the length of about 150 m. The division is implemented using Jersey barriers. I would not map this as a divided highway along the bend. At what length of dual carriageway would begin you draw the line, pun intended? I may bump up the recommendation above to 175m to 200m; 20m seems a bit short if you consider roundabout and junction divides to be separate entities from proper dual carriageways.
(05 Jun '11, 14:36)
Andrew Chadwick
Suggesting to use some judgement is probably a good idea. I might map your example as dual, but since it doesn't affect turning or contain any crossings or junctions (and it goes under two highway links) I'd probably keep things simple. My road in question is more of a sprawling patchwork urban horror.
(05 Jun '11, 14:38)
Andrew Chadwick
My suggestion is indeed a (limited) use of judgement, e.g. in the following cases:
(06 Jun '11, 10:57)
kay_D
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I've always mapped using a physical barrier = multiple ways.. ta Chris |
I'd just point out that there is a difference, in the UK at least, between different types of "diagonal hatched lines" - if they are bordered by a broken line you are free to enter the area when safe to do so, but when they are bordered by solid lines you aren't. Usually has more influence on overtaking than much else though.
@andy-allan Yep, this is in the UK. Hopefully insisting on some kind of physical barrier in addition will help make the distinction more obvious and verifiable. Probably we shouldn't count just wedges of lane divider marking on their own.
Perhaps another criterion is to ask "can a U-turn (normally) be made here?"
There's a section on this funny old wiki page: Editing Standards and Conventions ...on the topic. Doesn't answer you question though. Maybe you could lay down some guidelines there, if your ideas are accepted.
In the UK, a dual carriageway must have a physical barrier between the two directions of traffic. The "consist of diagonal hatched lines" is insufficient to make it a DC. This is important because the N speed limit on a DC is 70mph (versus 60mph). Using as one's defence for traveling at 65mph (when NSL is in force) that "there are hatched lines" is unlikely to work !