[Talk-us] US Trunk road tagging

[Minh Nguyen]

Vào lúc 11:00 2021-05-06, Paul Johnson đã viết:
> On Thu, May 6, 2021 at 12:43 PM Kevin Kenny <kevin.b.kenny at gmail.com> wrote:
>>
>>
>>
>> On Thu, May 6, 2021, 13:30 Roff, Thomas (FHWA) via Talk-us <talk-us at openstreetmap.org> wrote:
>>>
>>> On the point of definition of an Expressway. We usually refer the Highway Capacity Manual for their definition. However, I am not sure if there is a legal definition in the US.
>>
>>
>> There may be in some states. Around me, 'expressway' and 'freeway' are pretty much synonymous, so I actually have no idea what 'expressway=yes' might mean.
> 
> I feel like Oregon/Washington have the strongest grasp on this, being
> any two lane grade-seperated controlled access road (so, single
> carriageway freeway type situation) or any dual carriageway high speed
> freeway like road with intersections (including at terminus).

In traffic engineering jargon, "freeway" refers to a controlled-access 
divided highway, while "expressway" refers to a limited-access divided 
highway or sometimes a controlled-access undivided highway ("super 
two"). As far as I can tell, the MUTCD doesn't define "expressway" 
explicitly, but it uses this term frequently, usually in the phrase 
"freeways and expressways". Occasionally, it distinguishes expressways 
when discussing at-grade intersections, which don't apply to freeways.

The general public is primarily exposed to this jargon through the 
standard EXPRESSWAY ENDS XX MILES (W19-2) and EXPRESSWAY ENDS (W19-4) 
signs, as opposed to FREEWAY ENDS XX MILES (W19-1) and FREEWAY ENDS 
(W19-3) signs. In California, one can also identify an expressway by the 
lack of a FREEWAY ENTRANCE (G92) sign at each entrance ramp or the 
presence of an incongruous Advisory Exit Speed (W13-2) or Advisory Ramp 
Speed (W13-3) sign near an at-grade intersection. [1] In the Northeast, 
some expressways have numbered exits even at signalized intersections. [2]

Outside the U.S., there may not be any explicit expressway sign, which 
makes it awkward that we've been applying this distinction to the 
globally relevant highway=trunk tag. [3] The orthogonal expressway=* key 
was originally proposed by a fellow Ohioan mapper who, like me, felt it 
useful to explicitly indicate a limited-access divided highway, 
regardless of any other criteria for highway=trunk. [4] It would be 
helpful for maps that approximate the American cartographic convention 
of depicting expressways as double casing with a colored fill. Like many 
good ideas in OSM, the proposal itself was abandoned, but the key later 
become quite popular in the U.S., probably thanks to NE2.

There's a lot of misunderstanding about this key even within the U.S. 
because "expressway" has other definitions. In the Northeast and beyond, 
plenty of freeways are named "Expressway" despite being built to 
Interstate standards. On the other hand, in parts of California, 
"Expressway" only occurs in the names of non-freeways, and the 
distinction between freeways and expressways figures large in the public 
consciousness.

The term "expressway" is clearer in Western states where "freeway" is 
part of everyday language, but it's confusing in places where the 
equivalent term for "freeway" is "highway" (most of the rest of the 
country) or "turnpike" (hello Maine). In hindsight, a less overloaded 
term would've led to less misunderstanding and perhaps better software 
support. access_control=* has seen some use for this purpose. [5]

As an aside, I'd encourage you all to take the Dialects of American 
English Survey. [6] It includes several mapping-related questions that 
may be eye-opening to those who haven't moved around the country. Try 
clicking on each of the answers to peek at where it's most common before 
submitting your own honest answer.

[1] https://commons.wikimedia.org/wiki/File:San_Tomas_Expressway.jpg
[2] https://www.eastcoastroads.com/states/ny/parkways/sawmill
[3] 
https://lists.openstreetmap.org/pipermail/tagging/2021-February/059920.html
[4] 
https://wiki.openstreetmap.org/wiki/Proposed_features/Expressway_indication
[5] 
https://wiki.openstreetmap.org/wiki/Talk:Key:expressway#Applicability_to_Super_Twos
[6] https://www.dialectsofenglish.com/

-- 
minh at nguyen.cincinnati.oh.us