I'm back with more questions
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Was MS 18 ever officially split, and does it have a concurrency with I-20 or US 80? I remember seeing somewhere in a log "East" and "West". But it's obvious now it has a hidden concurrency with one of the routes. MS 18 is signed as if it connects to US 80, but signs on I-20 suggests that it doesn't make it that far.
And US 51 is confusing.. Google maps, imaps, and most other maps show 51 using all of State Street, but it was moved from this alignment over 50 years ago! US 49 formerly used Medgar Evers Boulevard and Woodrow Wilson, but signage is strict on the fact 49 doesn't use the road anymore and maps are too. I think MDOT is just trying to fool people because they never removed the signs at the US 80 junction and signage along the 55 concurrency only occur past the state street exit.
MS 18 does not have a concurrency on US 80 or I-20. Never has had one. Miss. Code Ann. § 65-3-3 says the route runs from Port Gibson to US 80 in Jackson, then restarts at US 80 in Brandon and heads east. The signage is correct.
The remaining US 51 signs at US 80 in theory should be removed or changed to "To US 51" to match the "To I-55" signage. I'd chalk it up as an oversight especially since everything at the interchange is antiquated. MDOT eventually removed all of the green signage at I-20 that indicate US 51 using State St. State St itself does not have any US 51 signage north of US 80.
MDOT moved US 49 off Medgar Evers Blvd and Woodrow Wilson Ave in 1987 and changed the signage correctly at that time. Unlike other old sections of US 49 that became MS 149, MDOT relinquished all control back to the city.
The Google maps, in many aspects, are not right. I'm not sure how they show US 51 using State St especially since it hasn't been a state maintained highway since either the mid 1950s or the early 1970s depending on the section.