Hi All, I’m looking to start a discussion about this road Way: B4257 (120457523) | OpenStreetMap, i’ve also recorded some mapillary imagery which can be found here Mapillary. This road has 2 lanes of traffic, one in each direction separated mostly with a painted area of diagonal stripes with a broken white line on both sides along with 4 crossing islands.
I’m torn on the best way to map this road correctly. I’ve listed below the 3 most viable options that I can see and the pros and cons from my perspective. I hope you all can lend me some input on this.
A single way. The first option would be to map it entirely as a single carriageway with a single way utilizing island nodes along the way. I don’t like the amount of detail you lose from the map doing this. You lose the ability to map the islands crossings in their entire detail and in my option is a less accurate representation of the world.
Two ways. The second option would be what I currently use here which is to map it as a dual carriageway with a separate way for each direction. This has the advantage of being more accurate and allowing the islands to be mapped separately However there are issues. This road does not meet the accepted definition of a dual carriageway since a dual carriageway requires the lanes to be physically separated by a barrier or something similar which is absolutely not the case the majority of this road which is separated by paint. Two ways also prevents a u-turn being performed on this section which does not match reality since it has a broken white line on the separating section which allows u-turns to be performed.
A mixture of both. The last option would be to map it as a dual carriageway around the islands and a single between. This is would allow for the most accurate representation data wise and solves the problems listed before. However visually its not very appealing and does result in a much larger number of ways.
It is not a dual carriageway. It is a single carriageway with a diagonal lines separating lanes. It is not the norm (at least in the UK), to create two seperate ways where a carriageway is separated only by diagonal line markings. We also do not separate for islands. The carriageway should be mapped as a single way. Nodes should be along the single way for crossing points, with appropriate tags for the island.
For this case I personally would map the pavement (footway) separately since it clarifies pedestrian use.
There are situations where we map lanes of a separately. Main example being through major junctions.
This default approach does clash with a desire to map area in detail. A few proposals have been made, but nothing has happened.
This is not true, please looks at footway=traffic_island on the wiki. Its a completely acceptable alternative to split the road around the island using the footway=traffic_island and footway=crossing tags instead of the crossing:island tag. here is also an example I very quickly found in Cardiff OpenStreetMap
Which is fine in a sunny day scenario when everything goes to plan.
If they are mapped as a dual carriageway then U turns are not possible unless crossovers are mapped. The result of this is when you hit a not moving traffic jam and you tell that satnav to avoid the next n hundred metres it will not plan a perfectly legal U turn.
The OSM wiki requires a dual carriageway to be two roadways separated physically - but there are exceptions in the exceptions paragraph
My observations when travelling is that on lower speed roads many local authorities will use paint or rumble strips to separate lanes of traffic with the specific intention of creating separation - and more importantly to save money.
Euxton Lane in Chorley is one such scheme I and others have mapped as dual carriageways - OpenStreetMap
when driving the experience is similar to that of a dual carriageway.
I am in favour of kitsee’s option 2.
If you map the roads as a dual carriageway, you can sometimes get away with 2. if u-turns are disallowed, which isn’t the case here. Arguably, option 2 is also less detailed if you consider that the middle lane (as much as we intuitively ignore it) cannot be easily mapped this way.
Maybe in the far future we all just map the barrier=kerb and the renderer just figures it out itself - but that is far away. Until then, option 3 is the best way forward if you want to keep that detail.
Yeah, I missed adding context. According to the Wiki (which is hopefully accurate for the UK?) option 1 is a valid way to map the situation. However, and that’s where I missed the context, if you choose to draw them separately (i.e. option 2 or option 3), then option 3 is preferable.
I don’t map in the UK, so if the rules there vary wildly from everywhere else, I will stand corrected.
Don’t want this to be read as a “keep off my garden” type of post.
There is an issue of etiquette when posting to a community category for a specific country. Different countries do have slightly different practices, necessary due to different legislation. Care is needed when posting if you’re not knowledgeable(?) about the country. Care is needed if question may require local/regional knowledge (eg local laws), and especially if the post is seeking views of a national community.
Getting back to the original road…
On the ground this is a single carriageway according UK legislation. But we’re not mapping UK legislation, and need to find the best fit for OSM Data.
Mapping as two carriageways implies different legislation. An example is that the OSM data would fail to allow a lawful a U-Turn. But we do split at junctions with complex lanes
UK roads in urban areas have numerous “unmarked” crossings with a pedestrian refuge. Creating a “micro dual-carriageway” for every single pedestrian refuge is not the default way of tagging in the UK. It feels like mapping for the renderer, or putting bicycle=no on 70mph Dual Carriageways.
I recognise the approach I suggest has problems. I specifically have issues where the island is big and the crossing points are not opposite each other.
There is also the problem of some regional highway authorities creating cheap & fake dual carriageways by using diagonal stripes bounded by solid white lines.
The existing simple highway tagging that we have does not work well for these situation. No easy answer. But mapping as a single carriageway causes less problems
If it’s a large staggered crossing like the one in the photo in the post directly above, then I’d split the main carriageway around it, as that’s the only way you can accurately micromap the crossing route, and get the crossing locations in the right place on each side.
But for smaller crossing islands (including the common case of those without signals) I probably wouldn’t split the main road, and I’d just use crossing:island=yes on the node instead.
Agreed. This section of road consists mostly of a painted hatched centre marking, with the four intermediate islands being quite small. Much wider or longer islands, and those Robert mentions which form part of a staggered crossing would be better with the road mapped as two separate oneway ways. However, for simplicity (and for better aesthetics on the map) the road here should be mapped as a single way with nodes representing the crossing points. The same level of detail can be added with this setup.
That should not be mapped as two separate ways, as the vast majority of that road has the lanes separated by paint alone. As per the wiki for the ‘dual_carriageway’ tag:
"Roads are not to be mapped as dual carriageways if the two directions are only separated
by paint. This includes single or multiple painted centre lines, hatched areas, channelized turn lanes, two-way turn lanes,
by flush medians,
or by any other means that is not a physical barrier to vehicles"
So to give this thread a conclusion, I’ve now remapped the road in question which is viewable here Way: B4257 (120457523) | OpenStreetMap. I’ve chosen to fix this street by having the highway split around the islands.
I agree with trigpoint that it cannot be a duel carriageway as it does allow U-turns, If it didn’t there would be more of an argument for bending the physical separation rule. Jofban also makes a fair point that the “intersection” with Carno St is structure like a T-junction with a turning lane which would be hard to represent with a dual carriage way. not impossible but not easy or neat.
I agree with Robert and others that a node with crossing:island=yes is a completely acceptable method of mapping a crossing and has its place however I do not agree that a tagged node a equivalent or superior to splitting the highway and adding a island area as it less accurately represents what is on the ground. It is an acceptable compromise for the sake of mapping large amounts of features in a short amount of time but I do not believe it should be considered anything more than a stop gap as the overall level of detail of OSM increases over time and eventually in a perfect future they should all be replaced.
To try and emphasize my point I’ve increased the level of detail of this road to include sidewalks, crossings and islands. This town is a pet project of mine, I’m trying to map it entirely to a micro mapping level of detail, its still a long way off but this road is much closer to what I consider to be an end goal for OSM at least in my opinion.
I still fail to see how this is the case. A node can represent exactly the same situation as splitting the way can for a single traffic island. In this case a single node can also be more aesthetically pleasing than this resulting view of the road as per your recent edit:
I’m afraid you may have fallen into the trap of mapping for the renderer. And I’m saying this not just to this post but to your recent edits. I am mapping for the data consumer as OSM is first and foremost a database, not a pretty map and its data is not used only for maps.
A situation like highways surrounding a island should be rather easy to detect programmatically so if you wish to make it more aesthetically pleasing then I suggest you seek out or develop a renderer that displays this in a more pleasing way.
Well, yes except for the island’s area which in this case is quite small. Obviously the data in OSM is not just for viewing, and is more important for providers to get data from and access. With that in mind, unless the shapes of traffic islands are very important for data consumers, again I fail to see how a node representing this is in any way worse than what you have mapped.
what if I say I’m a data consumer. I run my own website call opentrafficislands.com. so the data is important to me. Would that satisfy you? The thing is to the data consumer all data is important because you cannot presume who they are or who they will be in the future or how the data is and will be used. Since the data consumer is unknowable then we must assume they want everything and any simplification at the cost of information hurts them.
