[Talk-us] Prima Facie Speed Limits

Tod Fitch tod at fitchdesign.com
Tue Sep 9 15:09:39 UTC 2014

On Sep 9, 2014, at 6:10 AM, Andrew Guertin wrote:

> On 09/08/2014 05:27 PM, Tod Fitch wrote:
>> [...]
>> instead there is a state wide prima facie limit:
>> "source:maxspeed=US:CA:residential"
>> [...]
> My state doesn't have such a limit, but my city does. Supposing I started tagging things with source:maxspeed=US:VT:Burlington, would anyone be upset that "Burlington" and "residential" are in the same place in the hierarchy?
> (I'm hoping the answer here is no one cares, the value isn't intended to be machine parsable, and both values are understandable by humans.)

I think there are two reasons for the source:maxspeed tag:

1) So the next mapper who touches the maxspeed value knows where it came from.
2) To be able to find all the occurrences of maxspeed that were determined by the source. Something searchable but not necessarily machine parseable should be okay.

On Sep 8, 2014, at 10:30 PM, Marc Gemis wrote:
> In Europe (at least Germany, Belgium, The Netherlands, UK) people started to add both source:maxspeed=<country code>:<classification> and explicit maxspeed tags. Then there is no need for an external DB to lookup the speeds. Although it means that when the speed changes, all roads have to be retagged.

As long as the source:maxspeed value is unique to the jurisdiction then it is easy to find all the roads that need to be retagged.

On Sep 8, 2014, at 3:58 PM, Richard Welty wrote:

> the default speed limit in NYS for unposted roads is 55mph, irrespective of surface type. other states vary; there's a page in the OSM wiki about it.

If I recall correctly, NYS changed their rural highways from 50 MPH to 55 MPH when the nationwide 55 MPH limit came into effect in the early 1970s. So these speeds can definitely change, though usually change is slow.

I think that if the value for the source:maxspeed tag uniquely specifies the jurisdiction and is something that is readily understandable by a human then is should be okay. So US:CA:residential and US:VT:Burlington or US:VT:Burlington:residential would meet those requirements.

Sounds like the responders to this thread are either unopposed or generally in favor of the concept. I think I'll start tagging this way in my local area.


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