Author Topic: I-485 Charlotte Format  (Read 308 times)

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Offline ohroadscholar

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I-485 Charlotte Format
« on: September 20, 2020, 06:00:08 pm »
I was noticing that on NC I-485 around Charlotte that waypoints start and end at MM30, not MM0 like typical beltways.  So if I traveled between 51 and 10 passing MM0 on the southside can I mark it as NC I-485 51 10 or do I have to split it up?

Offline yakra

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Re: I-485 Charlotte Format
« Reply #1 on: September 20, 2020, 07:33:57 pm »
NC I-485 51 10 should work.

I was noticing that on NC I-485 around Charlotte that waypoints start and end at MM30, not MM0 like typical beltways.
Your intuition is right here; one needs to look at where the route starts and ends. Every TM route can be thought of as a line. Sometimes, these lines happen to start & end at the same place.
Clinched segments are connected along this line -- you get the segments between 51 and 10.
Now, if you had passed along the north side, via TM's begin/end @ MM30 aka I-85(48)? Then the .list line above would show the opposite of what you want, and you'd need to split it up. One line from Exit 51 to the beginning, and another line from Exit 10 to the end.

So, don't be confused by where a MM0 ever is. You just need to pay attention to where TM's beginning & end are.
(Think of a loop that would look more normal with just crossroad style labels and no exit numbers, such as TXLp7...)


Why's I-485 so weird?
When Tim first created "Clinched Interstate Mapping", I-485 wasn't a complete loop, and the exit numbers just reset in the middle of the partial loop. So, he created a single file for the route as it existed at that time.
When the loop was finally completed in 2015, Oscar extended the route by adding the new points on to the end of the line. He kept the existing point ordering, because to do otherwise would mess up people's .list files.

Meanwhile, in Canada...
AB201 is split up into two segments to avoid this exact situation.
When the loop is complete, the segments can all be joined together in the right order in a way that maintains .list compatibility, the same way that I-74Sea, I-74_E, I-74FutEll and I-74FutHig all refer to NC I-74Hig now.
This feature wasn't introduced until CHM was several years old, so this kind of future-proofing wouldn't have even crossed Tim's mind in the early days. By then, I-485 as we know (knew?) it was well established, as were people's .list lines. And so it is what it is...
« Last Edit: September 20, 2020, 10:01:24 pm by yakra »

Offline ohroadscholar

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Re: I-485 Charlotte Format
« Reply #2 on: September 29, 2020, 08:58:41 pm »
Thanks for clearing that up.

Offline oscar

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Re: I-485 Charlotte Format
« Reply #3 on: September 29, 2020, 09:38:17 pm »
Meanwhile, in Canada...
AB201 is split up into two segments to avoid this exact situation.

And so was AB216, while it was an incomplete loop around Edmonton. That made things much easier for yakra, and TM users, when the loop was completed, at which point the route files were combined without breaking any list files.
« Last Edit: September 30, 2020, 11:48:51 am by oscar »