[Talk-us] [Talk-us-newyork] Highway classification guidelines for New York State

[Minh Nguyen]

Vào lúc 16:47 2021-09-12, Eric Patrick đã viết:
> I have a thought regarding trunks in regards to functional 
> classification, and this is going to come from a different viewpoint. 
> Why not make Primary Arterials trunk roads, from a coding standpoint. 
> They're coded lower than a motorway, but higher than everything else. 
> Any GPS system will use the highest coded route, with the fewest 
> penalties, they can get to between points A and B. I understand that in 
> doing this, a lot of downtown areas will look like a sea of red, due to 
> the density of the Primary Arterials within those areas (cue Brian's 
> groan about this).

As far as I can tell, no mainstream OSM-based router directly penalizes 
a road based on its highway=* value per se. If it lacks a maxspeed=* tag 
and real-time or historical traffic data is unavailable or unsupported, 
then the router would assume a speed limit based on the highway=* value. 
 From what I've seen, these assumptions are usually wrong for... just 
about everywhere.

There may also be heuristics around avoiding the use of lower-classed 
roads once you're on a higher-classed road until you get close to the 
destination, but it isn't clear to me that these heuristics play a large 
role or that the changes being debated here would affect it very much. 
The idea is mainly to avoid divebombing onto an off- and on-ramp or 
cutting through a residential neighborhood -- shortcuts measured in feet 
rather than miles.

> Functional classification isn't going for looks, 
> though, it's going for function. The states have spent a lot of time and 
> effort since FC was first introduced about a decade ago.

OK, but is it a good fit? The highway=* key (other than 
highway=motorway) is defined as indicating the road's importance in the 
road network. [1] That sounds vaguely functional. But the ultimate goal 
of this key is indeed "going for looks", and optimal routing behavior, 
because OSM data is primarily used by renderers and routers.

Here's how the FHWA describes the purpose of functional classification: [2]

> Federal legislation continues to use functional classification in determining eligibility for funding under the Federal-aid program. Transportation agencies describe roadway system performance, benchmarks and targets by functional classification. As agencies continue to move towards a more performance-based management approach, functional classification will be an increasingly important consideration in setting expectations and measuring outcomes for preservation, mobility and safety.

The most we could say is that the two systems end up addressing somewhat 
overlapping sets of needs. But as elegant as FHWA functional 
classification may be on its own, shoehorning it into the existing 
highway=* tagging scheme would not be as clean as using a dedicated key 
like HFCS=*, because highway=* was originally designed by non-Americans 
who had no idea about the FHWA's specific functional classifications and 
it has come to be used by data consumers who also couldn't rely on FHWA 
definitions.

Other Principal Arterials also came up back in May in a discussion about 
correlating the National Highway System to highway=trunk. It's worth 
consideration as a starting point, but I'm pretty sure we'd need to 
distinguish between urban and rural principal arterials. When I looked 
into it for California, I found that this one functional class includes 
a wide variety of roads with starkly different levels of accessibility 
and mobility, even within a single urban area. [3]

[1] 
https://wiki.openstreetmap.org/wiki/Proposed_features/Highway_key_voting_importance
[2] 
https://www.fhwa.dot.gov/planning%20/processes/statewide/related/highway_functional_classifications/section01.cfm
[3] https://lists.openstreetmap.org/pipermail/talk-us/2021-May/021054.html

-- 
minh at nguyen.cincinnati.oh.us