When I think about kerb=lowered, I picture a sidewalk that is higher than street level with a ramp leading down to the lowered curb. The ramp is fairly short with a noticeable incline. Like these:
When I think about kerb=flush I picture a sidewalk that is at (or very close to) street level so any change of incline is not really noticeable as one approaches the curb cut. Like these:
But what about a longer ramp leading to a level sidewalk section at the lowered curb, like this?
Or these parallel ramps also leading to a level sidewalk section at street grade?
Or this very gradual ramp?
Would you say these are kerb=lowered or kerb=flush and why?
Essentially I’m trying to understand if the distinction here is just about curb height, or if the ramp angle and approach matters as well.
In all three cases I use kerb=flush because the ramp / incline happens at the footpath (and affects every pedestrian, not just crossing ones) rather than at the curb/kerb:
Unambiguously kerb=flush because the incline ends even before the crossing.
Similar to above, the footpath itself lowers in that place and the kerb simply follows suit.
This is a bit of a tricky example but like in the previous ones, the footpath itself is lowering and no curb cuts are used alongside how the include is more gradual than on a typical curb cut.
On that aside:
I consider this to be kerb=lowered not necessarily because it’s a slope on a kerb but rather because the kerb stands out a little from the road way (there’s a little bump when rolling on it) unlike the other image which is a clear kerb ramp (it’s still a case of a dropped kerb, though, because the level is definitively higher usually).
I’d use lowered_and_sloped as an offering in the pick list for the latter. Some are pure ankle breakers since they have a regular curb till the top of the slope into the sidewalk, just wide enough to fit a wheelchair or pram.
Ok, so then a short curb ramp where the incline is noticeable by feel, but where the curb itself is flush with the street would be kerb=flush? Like this one here:
This image is currently an example of kerb=loweredon the wiki, but maybe that’s not quite right?
I find it quite hard to grasp the dimensions in this image. I cannot tell if the strip between kerb and sidewalk / the ramp is 50cm or 150cm. It is an unfortunate angle / perspective. Therefore I would not take this image as example image for any tagging.
I considered adding on to that topic but there wasn’t really any discussion of kerb=flush so I decided to start a new one. Although I guess the resulting wiki edit is relevant here too. kerb=lowered is now described as a height of less than or approximately equal to 3cm and kerb=flush is described as a height of approximately 0cm. If lowered and flush can both be ~0cm high then I’m wondering what the remaining difference between them there would be. Hence my questions about ramp inclines and such. If the distinction is really only about kerb height, as a number of people have stated above, then I’d expect flush to be documented as approximately 0cm high and lowered to be documented as less than or approximately equal to 3cm high but greater than 0cm high. In simpler terms: lowered: small bump, flush no noticeable bump.
I think it would be nice if the tags on the curb node only had to do with the height. However, I suspect that the presence of some degree of ramp is valuable information for some users (maybe @UW_Amy_Bordenave can tell us about real-world uses if any), and we don’t currently have a way to describe the (relatively) steep slope of a curb ramp leading down to the flush curb. That is, the tagging on the curb node is being used to describe more than just the curb, but we don’t have a separate way to describe the presence of a ramp so it gets lumped in with the curb type.
Maybe. I haven’t thought through this a ton yet.
A lot of information is bundled into those single barrier=kerb nodes. This is unfortunate, because the result is effectively a “skunking” of kerb=* because different people tag kerb=flush and kerb=lowered in different ways - is it the “lip height” vertical displacement from roadbed to the start of the ramp/approach, or the “curb height” vertical displacement across a ramp from roadbed to sidepath level?
My rule of thumb - if there is a side slope, it’s a kerb=lowered. One must “lower” their elevation when traveling from the end of a sidewalk centerline down to roadbed level via a curb ramp.
Contrast that with a flush curb which is common, for example, at traffic islands. The traveler’s elevation does not change while going from road → traffic island → road, thus kerb=flush.
we do have tags for ramps, e.g. highway=footway footway=ramp (only 419 uses, but “logical”, not documented afaik), and ramp=* which is a property and according to its definition to be used on stairways (but could also be used as a property for ramps on other features) ramp | Keys | OpenStreetMap Taginfo
Generally, you can use any tag in OpenStreetMap, that’s why “we had to lump it into another tag because there was no specific one” never is a good excuse
On that aside, I’ve been occasionally using kerb=sloped, albeit for sloped kerbs as pure barriers (e.g. on traffic islands) rather than curb cuts / kerb ramps.
Frankly, the use of kerb=lowered for kerb ramps may be considered skunked because they’re placed in together with dropped kerbs purely by similar function but otherwise can’t be distinguished on OSM otherwise.
Alternatively (if not in addition to kerb=sloped), we use tags like angle and width for an accurate kerb profile.
If the presence of a curb ramp isn’t a good reason to tag kerb=lowered, then changes to the Wiki and to StreetComplete would be warranted. While describing the lowered value, the wiki page for kerb=* states:
Some names for objects that fall into this category include … curb ramp, … pram ramp, and kerb ramp
The StreetComplete question “What’s the height of this curb?” offers an option labeled “Curb ramp” with the same photo as the wiki. Selecting this option results in a kerb=lowered tag.
On the other hand, maybe the consensus is that kerb=lowered means either a little bit of a bump at the curb and/or a curb ramp. The question I have in that case would be what if the ramp is very gradual? Is that flush then because the incline change is hard to detect by feel? What incline would be a distinction between lowered and flush?
So that brings us back to using a separate tag like ramp=* to indicate presence of a ramp leading up to the curb. It doesn’t solve the problem of whether something is a ramp or not, but it means kerb=* could be used to tag only, well, information about the curb itself.
That said, if there’s interest in separating curb height and curb ramp into separate tags, I think we should use something other than kerb=* (perhaps kerb_height=*) to mitigate skunking.
This is a pre fabricated concrete block. 75 cm long 10 cm height.
Is this a kerb?
The functionality, is the same as the hand made examples above.
For wheelchair it does the same.
A lot of the flush ones are drainage channels as you noted, and as such not curbs.
lowered to me means (independent of the actual height) that the curb has some height above the carriageway (curb=raised) but is lower at this point for some reason (e.g. a driveway).
As for the ridges, best would probably be a separate line with Tag:waterway=drain - OpenStreetMap Wiki, though not sure if that is overkill. Maybe a drainage_channel=yes/no/0.1cm kind of tag could be introduced.
This image is actually also a good example of the two main curb edge types: returned curbs (left side) and side slopes (right side).
We have collected/annotated additional images of different pedestrian infrastructure configurations in TaskarCenterAtUW/tdei-tools/images (all CC0!).
I highly recommend anyone interested in a US perspective on these topics reads through PROWAG - that is what’s driving a lot of the ongoing standards/mapping/tagging development, whether that’s the (brace yourselves for acronym overload…) OSM US’s PWG, UW TCAT’s OSW, USDOT BTS NC-BPAID’s GATIS, USDOT FHWA’s MIRE, etc.
.jpg)
