So that is what inaccessible road is!
This article explains the typical routing problems validated with the routing vaildator based on OSRM data, and also contains the guidelines how to fix these problems.
Please take note it is currently under translation from Russian, and please forgive us for possible grammar mistakes.
Please note that this is an automated test. There can be false-positives. Some of the cases are not currently fixable due to OSRM lack of features (There are some known issues in OSRM routing). Also, not every problem can be fixed without local knowledge. To fix some problems properly survey can be necessary. Please make only changes in which you are absolutely sure.
Whole world vs you local area
Openstreetmap is the map of the whole world, and everybody can edit it. However, it is preferable to fix problems in area in which you know the community, conventions, language and possess local knowledge.
It is possible to get routing problems from particular area. Url should be modified in the following way:
- London - http://peirce.gis-lab.ru/fixme/p0/51.51,-0.13
- Moscow - http://peirce.gis-lab.ru/fixme/p0/55.7,37.6
1. Single isolated way
The pretty often and a very simple problem. The way is not connected to any other way. On the related example it is the service way. Due the programming issues, the validator marks only the part of the unconnected way, you can see the pointer at it.
How to fix: Make the connection to other ways by mapping the missing roads. If survey is not possible, the imagery or the GPS-tracks should help. On the related example the service way would be connected either to the secondary way named Snezhnaya ulitsa at the north-west end, or to the unnamed residential street at the south-east end.
2. Complex of isolated ways
A bit more difficult. A few ways are connected together but this connection has no links to other highways around.
How to fix: Like the previous problem. Make the connection to other ways by mapping the missing roads. This might require survey if the connections are not obvious from aerial imagery or traces. Watch out for tags if one of the existing ways is extended by the editor.
On the example the residential way as part of whole road system are connected to the service ways via area tagged with highway=* + area=yes. Most of the routing services, including OSRM, don't route the areas tagged this manner, so the service ways have become isolated.
How to fix: Add the linear road through the area to connect the isolated ways to other roads (on the example it would be the way from residential street to service ways, tagged with highway=service) and change tags on area from area=yes + highway=<type_of_road> to area:highway=<type_of_road>. Watch out for tags if one of the existing ways is extended by the editor.
Seems okay, but only at the first look. The nodes marked with the pointer are not connected together, so technically one way just ends very closely to other one. Such kind of problem cannot be detected visually on the map, but easily recognized with the validation tools (including the JOSM's validator).
How to fix: Connect the nodes together, using the hotkey "M" (or "Menu" -> "Tools" -> "Merge nodes") in JOSM.
5. No way?
There are few ways tagged highway=service (or highway=residential) connected together with one highway=track. The problem takes place, when a mapper confuses tracks with unpaved roads.
How to fix: Change the highway=* value of the wrong tagged road to set the right status and also add the surface=* tag. If you don't know the details, set the tags highway=unclassified and surface=unpaved.
6. Oneway road to nowhere
So it is. It allows to drive in, but there is no way out. Of course, there is something wrong with the map.
How to fix: Map the missed ways if any, or remove the surplus tag from some ways, or change necessary directions. This fix may seriously require the local knowledge.
7. Access denied
There are service ways on the private areas. Sometimes the part of that ways are forgotten to be tagged with access=private. Such problem is easy to detect visually by using mapnik, because it renders the private ways specially.
How to fix: Add the access=private tag.
On the example you can see the ferry way (tagged route=ferry + ferry=trunk … unclassified) what is connected to land road with the pier man_made=pier. But the piers are not routing objects so the ferry way is isolated.
How to fix: Add proper highway=* on the pier way. And check the other side of ferry way, please.
In some cases the validator shows places, where situation is very questionable or it is clearly alright. It may happen when the problem has already been fixed but the cache has not updated yet.
Lets see what other cases do no require fixing.
8. Go shopping
Oneway road going into the building. Yes, there are common situations in XXI century: it may be internal parking, or some sort of drive-in.
How to fix: It's not a serious problem for routing. But if you really want, you may map an roads scheme inside building. Note, that the question about tag for such internal roads is still open.
9. It's a trap!
Blocked with gate or lift gate oneway road leads to private area or parking. On the example the coming through parking road tagged with access=private.
How to fix: No need to fix. If you really want to do something, ask the owner of the area to make this way the turnpike. It may however be useful to tag the parking with access=private too, to avoid using it when the gates are open and being trapped when they close, and possibly to add opening_hours=* if still accessible sometimes (e.g. in commercial areas), and add toll information if needed!