[Talk-us] maxspeeds missing the mph

[Minh Nguyen]

Vào lúc 20:18 2022-06-13, Sobhan Mohammadpour đã viết:
> 
> Hi, i would like to edit the following ways in manhattan
> 
> <snip>
> 
> and add an |mph|​ to their maxspeed, according to
> https://wiki.openstreetmap.org/wiki/Key:maxspeed 
> <https://wiki.openstreetmap.org/wiki/Key:maxspeed>
> they need to have mph if they are in miles
> and
> https://www1.nyc.gov/html/dot/downloads/pdf/current-pre-vision-zero-speed-limit-maps.pdf <https://www1.nyc.gov/html/dot/downloads/pdf/current-pre-vision-zero-speed-limit-maps.pdf>
> suggest that they are indeed in miles per hour.
> 
> is this a safe change to do?

Yes, this is a good change to make. As it is, routers interpret these 
values as kilometers per hour. That doesn't significantly impact these 
lower-speed roads in terms of routing ETAs, but navigation applications 
will convert these values from km/h to mph and display misleading speed 
limits to the user.

Incidentally, I've started a MapRoulette challenge to clean up almost 
900 maxspeed=* values in California that are most likely tagged with the 
wrong unit:

<https://maproulette.org/browse/challenges/27812>

We've made good progress since yesterday but could always use some help. 
It's pretty straightforward to fix these issues, especially where 
street-level imagery is available. In urban areas of California, speed 
limits are generally marked on the pavement, always in mph, making the 
tasks even easier.

You can create a similar challenge for your state by adapting this 
Overpass query [1], which looks for multiples of 5 without an explicit unit:

   area(id:3600165475)->.searchArea; /* California area ID */
   way[~"^maxspeed"~"^[0-9]*[05]$"](area.searchArea);
   out geom;

Anecdotally, the bulk of these errors were introduced using JOSM and Go 
Map!!, which expect you to know the syntax for non-metric values. [2][3] 
A smaller number seem to have been caused by a bug in iD. [4] Some other 
issues I've seen:

* Lots of speed limits were applied only to the way adjacent to the 
speed limit sign, not to all the affected streets. Typically, only one 
speed limit sign is posted at the entrance of a residential subdivision, 
representing the "boundary" of a speed zone that applies to all the 
streets within unless otherwise posted. If all the entrances to a 
subdivision have a 25 mph speed limit, you can be pretty sure that it's 
at most 25 mph throughout.

* Some advisory speeds (the yellow signs) were tagged as legal speed 
limits for the whole length of the street instead of just 
maxspeed:advisory=* at the curve.

* Some school zone speed limits were mistaken for full-time speed 
limits. Depending on the situation, school zone speed limits are tagged 
maxspeed:conditional=* or maxspeed:variable=school_zone.

[1] 
<https://learn.maproulette.org/documentation/using-overpass-to-create-challenges/>
[2] https://josm.openstreetmap.de/ticket/19077
[3] https://github.com/bryceco/GoMap/issues/600
[4] https://github.com/openstreetmap/iD/issues/9110

-- 
minh at nguyen.cincinnati.oh.us