In the jurisdiction I live, I would apply the state’s default residential speed 
to OSM residential and unclassified highways. I would apply the state’s default 
55 MPH for untagged roads to OSM tertiary, secondary, primary and trunk 
highways. I would apply the state 65 MPH limit for freeways to OSM motorways.

If defaults are at the smallest enclosing administrative boundary probably not 
required in my area: One of the characteristics of tertiary, secondary, primary 
and trunk highways within a incorporated municipality and even in built up but 
non-incorporated areas, is that by law each of those road types must have the 
speed limit set based on a traffic study and signs are posted based on the 
decision made following the study. The end result is that non-residential, 
non-unclassified (using OSM terms) are pretty well signed in urban areas.

Tod

> On Sep 1, 2017, at 2:21 PM, Marc Gemis <marc.ge...@gmail.com> wrote:
> 
> Tod,
> 
> Can you clarify what residential and rural roads mean to you? Is a 
> residential road corresponding to the osm tag? When is a road rural? Can you 
> determine this for each osm way?
> 
> Regards
> 
> m
> 
> Op 1 sep. 2017 18:53 schreef "Tod Fitch" <t...@fitchdesign.com 
> <mailto:t...@fitchdesign.com>>:
> I take exception to the comment that “there will be too many exceptions to 
> the rule”.
> 
> In the country I live in each state has a set of “prima facia” speed limits 
> for various types of roads. Those are basically default speed limits to be 
> enforced unless otherwise posted by sign. Virtually no residential road in my 
> state has a speed limit sign but if you exceed 25 MPH you can be ticketed for 
> speeding. Rural highways are signed only at infrequent intervals, but 
> exceeding 55 MPH can result in a ticket.
> 
> Given:
> A) We should only tag what is on the ground verifiable. By that rule we 
> should not currently tag these “prima facia” speed limits (no speed limit 
> sign to verify a maxspeed tag value).
> 
> B) A routing app currently has no way to determine a default speed (one to be 
> used if no maxspeed=* tag found on way). These can vary by jurisdiction and I 
> can imagine situations where a national default is overridden by a state 
> default and/or local municipality default. Should all routing apps go to a 
> different geographical database to get defaults? If so, why not go to that 
> other database for everything and ignore OSM?
> 
> It make perfect sense to me to allow administrative areas to be tagged with 
> default values for otherwise untagged items within the jurisdiction. If 
> something deviates from the default, as in your “speed limits varies 
> depending on local topography”, then it will be signed and we should tag per 
> the sign. But many, many roads in my area are not signed and yet have legally 
> set maximum speeds.
> 
> At present, I usually ignore the local verifiability constraint and simply 
> put a maxspeed value on residential roads after I’ve surveyed them even if 
> they are not signed. If I am feeling a bit more energetic than usual I may 
> also add a source:maxspeed with a value citing my state’s motor vehicle code. 
> It would be a lot easier if I could rely on a default value set on my state’s 
> administrative boundary.
> 
> 
>> On Sep 1, 2017, at 9:25 AM, Dave F <davefoxfa...@btinternet.com 
>> <mailto:davefoxfa...@btinternet.com>> wrote:
>> 
>> Hi André
>> 
>> Assuming or defining a default should be based on the number of different 
>> values within the set. 
>> 
>> For the examples you give:
>> 
>> maxspeed shouldn't have a default. Apart from on motorway classed roads, 
>> speed limits varies depending on local topography. There will be too many 
>> exceptions to the rule.
>> 
>> driving_side is defined nationally so has a default. (I'm sure now someone 
>> will now provide examples where that's not the case).  Any router worth its 
>> salt, should be able to check which country it is in.
>> 
>> DaveF 
>> 
>> 
>> On 31/08/2017 12:49, André Pirard wrote:
>>> Hi,
>>> 
>>> Examples: either each road is tagged with maxspeed=* 
>>> <https://wiki.openstreetmap.org/wiki/Key:maxspeed> speed limit and 
>>> driving_side=* <https://wiki.openstreetmap.org/wiki/Key:driving_side> or 
>>> there are defaults.
>>> I'm reviving this remark because the examples are numerous:
>>> The Belgian Flemish community wants to tag maxspeed=* 
>>> <https://wiki.openstreetmap.org/wiki/Key:maxspeed> on every road instead of 
>>> using a default. Is this a new specification and where is it written? Must 
>>> that now be done in every country?
>>> The current language= proposition wants to do it without defining defaults. 
>>> Really? language= on every name= ?
>>> Other examples are maxheight in tunnels. Osmose just accused me of someone 
>>> else's omitting maxheight. It shouldn't be necessary if it's the default, 
>>> that is if there is no sign for it, but Osmose likes to yell just in case.
>>> countless etc.
>>> Please choose.
>>> 
>>> Either the defaults are in the OSM database and it takes just a routinely 
>>> map fetch to get them all updated timely,
>>> or each other router (GPS) writer implements them each their own way from 
>>> various random other files. It's not well clear how contributors ca update 
>>> all those files instead of OSM and it typically needs a full software 
>>> update for each little default change, depending on writer's availability.
>>> 
>>> Please choose.
>>> 
>>> There is a Proposed_features/Defaults 
>>> <https://wiki.openstreetmap.org/wiki/Proposed_features/Defaults> that puts 
>>> the defaults in OSM and it's an EXTREMELY HUGE mistake to have marked such 
>>> a paramount good work as abandoned because nobody continued the work.  For 
>>> the sake of OSM, especially routing, please reopen it.
>>> I don't claim that it is the good solution but I do claim we should work on 
>>> such a default database in priority.
>>> 
>>> I didn't analyze it in full depth, but I have the following remarks:
>>> - Why not allow the def keyword in the border relation itself? But it could 
>>> be called zzdef to cluster at the key end.
>>> - If a separate relation is preferred, it should be pointed at by a 
>>> "defaults" role in the corresponding border or other relations so that it 
>>> can be found.
>>> - to ease scanning a border tree upwards, a "parent" relation should exist 
>>> in border relations.
>>> 
>>> In hope of a well structured OSM,
>>> 
>>> Cheers 
>>> 
>>> André.
>>> 
>>> 
>>> 
>>> 
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