The wiki defines _link ways as connectors between highways, but does not address links that also provide direct property access or connect to local streets. What should their highway classification be in these cases?
The following cases are from Southern Brazil. (If you know of similar challenging cases in other regions, please share!) They are one-way U-turns with similar geometry along a trunk highway, only their connections and surroundings differ. Brazil’s highway classification (mostly functional and by importance) falls back on general OSM principles for highway link classification, not defining any criteria for this. The question I have is what should be the highway value of the following ways highlighted in magenta.
Street-level imagery is limited for these locations. If you choose “Other” in any poll, please explain in a reply.
Case A (location): U-turn connects to a tertiary street (urban way, not part of a major route). How should it be classified?
trunk_link
tertiary
Other
0voters
Case B (location): U-turn provides access to the front of residences. How should it be classified?
trunk_link
tertiary
unclassified
residential
Other
0voters
Case C (location): U-turn with same geometry and similar appearance from the ground, but no access to residences nor connections with urban streets. How should it be classified?
My general take is that roads often serve multiple functions at once, and in that case the highest classification should win. We already do this elsewhere: a road that links two settlements but also has residential frontage gets unclassified, tertiary or higher. Not sure why links would be treated differently.
The wiki’s focus on the “channelised” aspect of slip/ramp roads reflects a pretty Western infrastructure model. In many developing countries, ramps and U-turns tend to be more permeable and serve local access alongside their junction function, so applying that criterion too strictly doesn’t really work.
In general for the main purpose of that road is the key. In your samples it looks like the U-turn is kind the main function. So I would use *_link.
Ifvthe main function would be residential access or connecting the tertiary road, that might be different.
This is complicated. Eg when a curved road section is bypassed, a similar layout may be resulted, then one would be justifying based on how it’s built originally.
For A, if the terminating road doesn’t have an island, the section in between the terminating and through road functions as the minor road’s extension. Therefore, the island case can further consider the section between the minor road entry & exit separately.
Perception is affected by your drawing, and the alignment. If it’s straighter, longer, or channelized to favor the westbound exit, it may be seen as a frontage roadway.
There’s a fundamental question on why should channelized/curved right-in-right-out be =*_link but not as the terminating road. Straight islands can be used, then it would be inconsistent. Talk:Highway link - OpenStreetMap Wiki
If a road allows travel between 2 other roads (especially if not =service in other cases , or not the sole access), it may be argued as a frontage/collector road. They don’t travel through the =trunk , or other roads connected by the =*_link (when considered as the highest class) in concern.
If this is argued as a junction, throughabout / hamburger intersections use highway= + =circular similar to =roundabout , not highway=*_link
This mostly discusses choosing among the available highway=* , or highway=*_link , not highway=* vs =*_link , which are quite different. The reason would then be =primary / =secondary can’t be used following national rules, and you are forced to use =trunk_link , sacrificing the highway=* vs =*_link distinction.
The comparison between case A and throughabouts is indeed revealing since a throughabout can be used for U-turns but the circular ways are not classified as _link nonetheless.
The Brazilian highway classification system covers frontage roads indirectly, so if these structures are seen as frontage roads, the local rules would apply. For example, this U-turn along the same road is connected to frontage roads, and the section in magenta is currently classified as tertiary (it was trunk_link years ago, even if the other ways it connects to already existed; maybe it should be trunk_link? maybe it is correct as it is now?):
Many frontage roads in Brazil are not part of the major highway, being managed by a municipality rather than a state or federal government. In these cases, they are rarely present in official plans, but the few I’ve found often treat them as urban arterials (secondary). When plans are missing (which is the usual case), they follow the main local classification system and its implicit heuristics for filling in gaps by considering topology. If a frontage road is connecting the major highway to urban arterials, it is considered part of the urban arterial system to ensure connectivity, so it is classified as secondary or primary even if it has a lower speed limit than typical for arterials. If it connects to urban collectors, then it would be at least tertiary (part of the collector system), and may sometimes be mapped as secondary if it functions more like an urban arterial - with higher speed limit, relatively long and usually connected to the major highway at one end and to arterial ways or higher (often the same major highway) at the other.
