Expose hov:lanes and hov:minimum as raw text

[dsaderholm]

Would you consider outputting OSM's hov:lanes and hov:minimum as raw Text on MapdOut, the way conditionalSpeedLimit passes its tag through untouched?

The reason for raw rather than parsed: whether an HOV lane is usable depends on occupancy, tolling and local rules, none of which mapd should have to reason about. Your note on the conditional speed limit work says it best, that the tag is output so forks can evaluate what mapd does not handle itself. This is the same situation, and it keeps the ask to one Text field with no lane indexing in your code.

What it is for: my fork suggests lane changes to pass slower traffic, and today nothing in it knows an express lane exists. The leftmost lane is exactly where a pass goes.

Format, from 573 tagged ways on I-15 in Utah:

hov:lanes = "designated||||"      172       hov:minimum present on all 573
            "designated|||"       157       pipe count always matches lanes
            "designated|||||"     149
            "designated||||||"     92

designated is the first entry on every single one, so where the tag exists the HOV lane is the leftmost lane.

Coverage, measured along the whole corridor rather than one metro, because I got this wrong once already in another issue here:

I-15 Utah              1269 ways    45%
I-15 Arizona/Nevada     500 ways    22%
I-15 California         544 ways     0%

Worldwide, taginfo puts hov:lanes at 19,306 objects and hov:minimum at 11,419, so this is a US-and-Canada tag rather than a common one. lanes:hov is 212 objects and not worth reading.

Two honest caveats, since they bound what this buys you:

The California zero is not missing data. There the HOV lane is mapped as its own separate carriageway, and I measured 419 of 501 bare-hov ways in the LA basin carrying only 1 or 2 lanes. So hov:lanes on the matched way genuinely does not describe those roads, and exposing it would not help a consumer there. It helps where HOV is a lane inside the main carriageway, which is the Utah and Nevada pattern.

And this is squarely optional for you. It is a modest tag, in one region, and I would put it behind the overtaking work I mentioned in the other issue if you are choosing.

[dsaderholm]

Widening the measurement, since I filed this on Utah data alone and the interesting case turned out to be California.

designated leading the list is not a Utah artifact:

                     hov:lanes ways   designated leftmost
I-15 Utah                       322                  100%
I-15 Riverside CA               666                  100%
I-405/I-10 LA                   334                   98%
I-5 San Diego                   204                   94%

1,526 ways across four metros. So "the HOV lane is the leftmost lane" holds at 94% or better everywhere I looked, rather than the "every single one" I wrote above, and all four are 100% oneway so there is no direction ambiguity to resolve on these.

One thing I found while checking, which may be useful context rather than a request: where California keeps the HOV lane inside the main carriageway, the buffer that separates it is often mapped as change:lanes, e.g. no|not_left|yes|yes|yes|yes. That is lane 1 being the HOV lane you may not leave and lane 2 being unable to move left into it, which is the painted buffer stated as a tag. It only covers 27 of 240 such ways in the LA basin, so it is thin, but it means hov:lanes and change:lanes answer different halves of the same question and neither substitutes for the other.

Not asking you to expand the scope here. Just that if the change work in issue 129 ever happens, these two are more complementary than the separate issues make them look.