[Tagging] maxspeed:type vs source:maxspeed // StreetComplete

[Tobias Zwick]

This is an interesting idea (inspired by the ongoing discussion about
mapping language borders?), but unfortunately it wouldn't work.

Sorry for linking to this all the time but it is really necessary in
order to understand the big picture:
https://wiki.openstreetmap.org/wiki/Default_speed_limits

It wouldn't work because legislation on max speed is not that easy. Some
points:

1. OSM highway classifications (secondary,tertiary,...) do not and
   cannot follow the same scheme as how the roads are grouped for the
   purpose of defining different max speeds in legislation.

   Examples:
   - In California (US-CA), the default speed limit for residence
     districts and business districts is 25 mph. But there is no
     highway=business (etc.)
   - In Indiana (US-IN), the default speed limit on US interstates is
     70 mph. Now, not all highway=motorway are interstates and not
     all interstates are necessarily highway=motorway.

2. Max default speeds can depend not only on the road type / area but
   also on vehicle type, its designation and its properties (weight, no
   of seats, with trailer? ...), furthermore even on the time of day and
   weather condition.

   Examples: See Portugal (PT), see Poland (PL), European countries

3. (As hinted at by the last point) what road type category applies can
   not always be determined by looking at one tag (a "classification"
   of some kind) only.

   Examples:
   - In California (US-CA), any road with 2 or more lanes in *each*
     direction has a default speed limit of 65 mph
   - In Alabama (US-AL), the default speed limit for roads without
     alphalt or concrete surface is 35 mph (usually it is 55 mph).
   - In Germany (DE), there is no speed limit on dual carriageways
     and single carriageways with 2 or more lanes in each direction
     for passenger cars, independent on whether they are classified
     as motorways or motorroads or not

Cheers
Tobias

On 19/09/2018 08:01, Tod Fitch wrote:
> 
>> On Sep 18, 2018, at 6:19 PM, Joseph Eisenberg <joseph.eisenberg at gmail.com> wrote:
>>
>> So on the boundary=administrative admin_level=6 for Rogers County, we could have something like maxspeed:type:default=45mph
> 
> Except that more typically there will be different default speed limits on each of the various OSM highway classifications. So maybe something more like “maxspeed:default:residential=25 mph”.
> 
> But I imagine there are other types of tags that might benefit from the ability to give defaults for a geographic area. So possibly it would be better to have “default:maxspeed:residential=25 mph” where and entire “default:*” namespace is created. For California something like:
> 
> “default:maxspeed = 65 mph”     // State wide maximum for all roads unless otherwise tagged or overridden by a more specific default
> “default:maxspeed:primary = 55 mph”    // More specific default speed limits specific OSM road classifications
> “default:maxspeed:secondary = 55 mph”
> “default:maxspeed:tertiary = 55 mph”
> “default:maxspeed:unclassified = 30 mph”
> “default:maxspeed:residential = 30 mph”
> “default:maxspeed:service = 15 mph”
> 
> 
>> On Sep 18, 2018, at 10:15 PM, Mark Wagner <mark+osm at carnildo.com> wrote:
>>
>> . . .
>>
>> The third law: RCW 46.61.400(1).  "No person shall drive a vehicle on a
>> highway at a speed greater than is reasonable and prudent under the
>> conditions and having regard to the actual and potential hazards then
>> existing."
>>
>> As a highway engineer pointed out to me recently, most county roads,
>> especially unpaved ones, are designed around a speed limit of
>> "reasonable and prudent".  The 50 MPH limit established by RCW
>> 46.61.400(2)(b) simply sets a firm upper boundary; it's quite possible
>> to get a speeding ticket at a lower speed.
>>
>> Sure, you can put a number on any road.  But for most rural roads
>> without speed-limit signs, the number is unrelated to how fast you can
>> drive on that road.
>>
> 
> California, and I suspect most if not all other states, has a reasonable and prudent clause in the speed statutes too. So depending on conditions, especially weather conditions, theoretically you can get a speeding ticket while driving under the signed or prima facia speed limit.
> 
> However I think that is a diversionary argument that basically implies that we can’t tag any road with a speed limit because the default or signed speed limit can be trumped by a reasonable and prudent clause in the motor vehicle code.
> 
> I am a little curious about the highway engineer’s statement though. While not a civil engineer, I’ve had some interest in the field and the highway design books on my shelf (admittedly pretty old ones) all work off a design speed that is a specific number. Not a nebulous “reasonable and proper”. The design speed used to compute required sight distances, turn radii, ruling and maximum grades, etc.
> 
> 
> 
> 
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