[Talk-us] Speed limit editing in Detroit

Tod Fitch tod at fitchdesign.com
Sat May 6 14:18:27 UTC 2017


> On May 6, 2017, at 1:11 AM, Paul Johnson <baloo at ursamundi.org> wrote:
> 
> 
> 
> On Sat, May 6, 2017 at 3:07 AM, Paul Johnson <baloo at ursamundi.org <mailto:baloo at ursamundi.org>> wrote:
> 
> 
> On Fri, May 5, 2017 at 7:55 AM, Horea Meleg <horea.meleg at telenav.com <mailto:horea.meleg at telenav.com>> wrote:
> 
> A lot of motorway_links don’t have a speed limit sign. Do you have any idea where could we get the speed limit values from?
> In North America, ramps with speed limits are relatively rare, but following the usual rule that the previous speed limit applies, the speed limit of the off-ramp would be the same as the freeway itself unless otherwise posted, and if the same ramp returns to the freeway contiguously, that speed limit would continue to carry over to the on-ramp.  It's not very much more complicated than that, but in practice, just leave off maxspeed on the ramps entirely unless it's actually posted with a regulatory (white sign) speed limit or a general speed limit is known (both relatively uncommon). maxspeed:advisory would be far more common, as exit ramps are nearly universally posted with an advised (yellow sign) speed.
> 
> Adding to my own answer again, I should say rather than "in practice, just leave off maxspeed" but rather, "in practice, it never comes up so people rarely tag it."  I don't mind adding these if folks consider that favorable (I do see the value).
> 

From a end user of a routing app on my phone that uses OSM data, I’d rather have the maxspeed omitted from *_link ways if it is not signed. The reason is that there are some freeway/freeway ramp geometries where traveling by the ramp is slightly shorter than keeping on the freeway. I’ve seen cases where that caused the app I use to route me off the freeway and then immediately back on. If there is no maxspeed tag, I can set the default for the *_link such that I am not needlessly routed off and then back on a freeway.

I guess that is “omitting tags for the data consumer”, but since we are discussion situations where there is no sign and, in general, we tag what we see I don’t see that as being too far from the normal tagging philosophy.

Cheers,
Tod


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