[Tagging] Feature Proposal - RFC - cycle expressways

[Minh Nguyen]

Vào lúc 15:34 2022-08-05, Martin Koppenhoefer đã viết:
> 
> 
> sent from a phone
> 
>> On 5 Aug 2022, at 12:36, Pieter Vander Vennet <pietervdvn at posteo.net> wrote:
>>
>> As far as I know, a `motorway` is a road **with control of access**, i.e. this is a legal designation. If there is a traffic sign which forbids the use of non-car traffic, it should be mapped as motorway.
> 
> 
> motorways have specific signs (you link the wiki page later on in your mail). Access restrictions that allow the use only for cars exist as well, and the two should not be confused. The latter could for example come in the form of vehicle=no motorcar=yes

The proposal seems to refer to access control in the sense of physical 
access control, that is, restricting entering and exiting the pathway to 
certain designated points and blocking direct access from abutters. This 
is orthogonal to access restrictions in the sense of who or what may 
travel along the pathway. For example, a car would be legally allowed to 
use a motorway without restriction, even as it may only enter the 
motorway from a severely limited number of connecting roads, legally and 
practically.

A roadway can be converted to controlled access by blocking off all the 
driveways and minor streets and erecting a fence. I assume the same has 
been done for some cycle expressways. It would be impractical for a 
renderer to analyze the density of intersections or the porousness of 
fences along a landuse=highway just to decide what color to draw the 
highway=*.

A prolific mapper once blanketed a few U.S. states with access_control=* 
to explicitly indicate each road's level of access control. There's some 
merit to this idea. Ideally, a router would avoid snapping the 
destination to a controlled-access highway, because the route would stop 
right on the highway, where the user would see the destination but be 
unable to reach it. Moreover, some states post signs indicating where 
access control begins and ends. [1] California's highway department even 
posts their address on the fence specifically so that you can ask where 
the nearest highway entrance is located -- by mail. [2]

(OSM is revolutionizing navigation, let me tell you!)

However, access_control=* isn't more widely tagged because it's largely 
redundant to road classifications. The vast majority of freeways 
(highway=motorway) have controlled access by definiion, while the vast 
majority of surface streets (highway≠motorway) have uncontrolled access. 
In the U.S., the only gray area is what are 
technically/officially/regionally known as expressways (expressway=yes, 
distinct from highway=motorway). Limited access is characteristic of 
expressways, but so is inconsistency.

The American definition of an expressway [3] is so imprecise that, even 
though there's often a very prominent sign indicating the end of an 
expressway, there's never a sign indicating the beginning. The signs are 
not what make an expressway an expressway. Rather, the distinction is 
based on fuzzy attributes, such as access control and design speed; it's 
easier to tag an expressway if you don't think too hard about it. 
Unfortunately, the highway department would never respond to my 
typewritten letter asking which highways are considered expressways.

The cycleway=expressway proposal names several attributes that would be 
familiar to anyone who's had to tag expressways in the U.S. I offer my 
sympathy to anyone who finds it necessary to define a cycle expressway 
with scientific precision. Some things in life can only be classified by 
intuition. [4]

[1] https://commons.wikimedia.org/wiki/File:MUTCD-OH_R26-H2.svg
[2] https://commons.wikimedia.org/wiki/File:MUTCD-CA_S3-1.svg
[3] https://wiki.openstreetmap.org/wiki/Key:expressway#Characteristics
[4] https://en.wiktionary.org/wiki/b%C3%A1nh

-- 
minh at nguyen.cincinnati.oh.us