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Concurrency Routes

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Amaury:
So, we know that in concurrencies, there's always a primary route, and the mileposts that are used are based on what the primary route is. The other route(s), however, is/are still counting, you just don't see it. So, if State Route begins a concurrency with US Route at State Route milepost 50 and US Route milepost 200, and the concurrency lasts for 30 miles, when the concurrency ends at US Route milepost 230, the next milepost after the split for State Route would be milepost 81, not milepost 51.

We can tell which route is the primary route based on which one comes first on the reassurance shields, whether it's on top or on the left. Here, for example, Interstate 82 is the primary route, since its reassurance shield is on top. Likewise here for US Route 97 and Washington State Route 20. This one is the same thing, but instead of top to bottom, it's left to right. And here, the primary route is Interstate 82, the secondary route is US Route 12, and the tertiary route is US Route 97. Likewise, here, the primary route is Interstate 90, the secondary route is US Route 2, and the tertiary route is US Route 395.

We also know that the importance goes interstates >> US highways >> state highways. So, my question is when the concurrency involves two or more of the same type of route, how is it determined which one is the primary route? Here, SR 20 and SR 21 are both local state highways, with SR 20 being the primary/more important route. In Montana, there's a concurrency with Interstate 15 and Interstate 90, and Interstate 15 is considered to be the primary/more important route.

Quillz:
Iíve generally seen lower numbers get priority. But itís by no means a consistent rule.

amroad17:
I-64 has concurrencies with five odd north-south Interstate highways between St. Louis and the Hampton Roads area.  They are I-57, I-75, I-77, I-81, and I-95.  Each concurrency uses the odd number Interstateís mileposts and exit numbersómore than likely because each of the odd number Interstates were completed before I-64 was.  However, in four of the five cases the higher numbered Interstateís milepost and exit numbers were used.

Another example is I-20/I-59 in Mississippi.  I-59ís mileposts and exit numbers are used.

Quillz:

--- Quote from: Amaury on October 04, 2022, 01:49:25 AM ---We can tell which route is the primary route based on which one comes first on the reassurance shields, whether it's on top or on the left.

--- End quote ---
This isn't really reliable. In California, concurrencies technically do not exist at all. You have implied concurrencies, i.e. one route will exist but not signed. This isn't very consistent and more often than not, they do seem to be signed, but the order doesn't make sense. For example, during the brief CA-23/US-101 concurrency (more technically, CA-23 doesn't exist for a few miles while 101 bridges the gap), new signage in this area actually puts the 23 shield on top of the 101 shield. Not side to side. If anything, 101 shields should be on top. But they aren't. But then when you see CA-168/US-395, they are lined up side to side.

Rothman:

--- Quote from: amroad17 on October 04, 2022, 03:49:10 AM ---I-64 has concurrencies with five odd north-south Interstate highways between St. Louis and the Hampton Roads area.  They are I-57, I-75, I-77, I-81, and I-95.  Each concurrency uses the odd number Interstateís mileposts and exit numbersómore than likely because each of the odd number Interstates were completed before I-64 was.  However, in four of the five cases the higher numbered Interstateís milepost and exit numbers were used.

Another example is I-20/I-59 in Mississippi.  I-59ís mileposts and exit numbers are used.

--- End quote ---
And yet, the MUTCD has guidelines regarding which mileposts are used.

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