[Talk-us] Freeway directions

stevea steveaOSM at softworkers.com
Sat Oct 19 09:05:33 UTC 2013


>On Thu, Oct 17, 2013 at 3:39 PM, Brad Neuhauser 
><<mailto:brad.neuhauser at gmail.com>brad.neuhauser at gmail.com> wrote:
>
>From 
><http://en.wikipedia.org/wiki/Interstate_Highway_System#Primary_.28one-_and_two-digit.29_routes_.28contiguous_U.S..29>http://en.wikipedia.org/wiki/Interstate_Highway_System#Primary_.28one-_and_two-digit.29_routes_.28contiguous_U.S..29 
>:
>
>"In the numbering scheme, east-west highways are assigned even 
>numbers and north-south highways are assigned odd numbers. Odd route 
>numbers increase from west to east, and even-numbered routes 
>increase from south to north (to avoid confusion with the U.S. 
>Highways, which increase from east to west and north to south), 
>though there are exceptions to both principles in several locations."
>
>
>Field signage is sometimes inconsistent with the official rules; for 
>example, US 68 is mostly (entirely?) signed north-south, and I-69 
>becomes east-west between Lansing and Port Huron.  States may have 
>their own rules; some states (MS, FL) follow the even-odd rules that 
>the national routes do, some use an opposite pattern (even N-S, odd 
>E-W), and some have no pattern at all (GA, TN).
>
>There are also cases of signage by loop nesting ("inner" 
>clockwise/"outer" counterclockwise for RHD) - I-495 around 
>Washington and I-440 around Raleigh NC are examples, along with GA 
>10 Loop around Athens GA. And in Canada the QEW is "directionally" 
>signed by destination (Toronto on the clockwise carriageway, Niagara 
>and then Fort Erie on the counterclockwise one). There may be a few 
>more oddballs I've missed.
>
>
>IMO preferred practice should be a relation for each continuous 
>cardinal direction, to keep validation simple; undivided roads 
>should use forward/backward roles to distinguish which relation 
>applies to the underlying way's forward/backward traversal. It 
>shouldn't be too terribly hard to come up with an algorithm to fixup 
>the existing single-relation cases, particularly for the ones where 
>the routes are entirely dual carriageway, although occasionally the 
>heuristics will be wrong and need a manual edit.

Well said, Chris.  +1, lands right in the middle of where it might, imho.

Manual edits on exceptional cases means that somebody, somewhere is 
paying attention.  In a big set, with careful management, that's to 
be expected.  Good show.

Encore, author.  This is a serious project which aims to accurately 
map "what is."  Nice job so far, everybody.  I very much like this 
crowd-sourced map.  It only keeps getting better and better.

SteveA
California
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