[Talk-us] Freeway directions

James Mast rickmastfan67 at hotmail.com
Sat Oct 19 02:32:45 UTC 2013

Chris, the QEW has three "destinations" on the counterclockwise direction.  In addition to having Niagara and Fort Erie, between Toronto and Hamilton, it's posted for Hamilton.  After Hamilton, it then becomes Niagara.  I should know, I've traveled the QEW several times in my life.


From: lordsutch at gmail.com
Date: Fri, 18 Oct 2013 18:59:58 -0400
To: talk-us at openstreetmap.org
Subject: Re: [Talk-us] Freeway directions

On Thu, Oct 17, 2013 at 3:39 PM, Brad Neuhauser <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 :

"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.


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