There's also a route in Indiana (don't recall which one offhand) in usasf with at-grade intersections.
MDOT data is a bit ambiguous when it comes to what I had labeled US51SprJac. It was part of the former US 51 route through Jackson, but most of State St was turned back to the city and US 51 rerouted onto I-55 sometime in the 1980s. However, the southernmost leg (that area covered by US51SprJac) remained on the state highway system...and EVERYTHING on the state highway system has a route number, whether it's signed or not. I used US51SprJac because for many years, it continued to be signed as "US 51" (albeit without any banners). Given our general policy of not including numbered routes if they're not signed, I opted to remove US51SprJac now that it is no longer signed as "US 51".
Hope that clears things up.
Spent some time trying to find anything useful to clear the US 51 onto State St question.
US 51 South posting in 2011 on State St approaching US 80 -
https://goo.gl/maps/mXBCyS48bzJViqm96 - changed to TO US 49 by 2013
US 51 north leaving I-20/55 had a US 51 north BGS in 2011 -
https://goo.gl/maps/wCGHSwxkvv1GVitx5 - removed by 2013
US 51 South was explicit on the BGS from US 51 south approaching I-20/55 in 2011 and removed by 2013
US 80 WB has had no route marker at all for State St in the GMSV era and the same is true at the bottom of its ramp.
US 80 EB has a US 51 South marker on its most recent GMSV of June 2018 -
https://goo.gl/maps/nqqasxdenmiSJND27. The ramp at the bottom has had only a US 51 shield sans banner pointing to the right during the GMSV era
I-20 WB had a US 51 North BGS up through 2011 -
https://goo.gl/maps/2ykibtcPU2G8qTd67 - changed to just State St by 2013. Same is true for I-55 NB approaching I-20.
I-20 EB had a US 51 North BGS up through 2007 and was removed by 2011.
There were no US 51 south references on either direction of I-20 in the GMSV era, despite US 51 being well posted on I-55 south of Jackson.
On the north end, there are also Begin/End maintenance signs on State street a little south of County Line Rd. There is a sole US 51 south trailblazer to leave State at County Line but no indication to get on I-55 south and US 51 does not appear to be posted anywhere on I-55 north of I-20.
I checked a bunch of MDOT resources and found no designation for State St where still maintained as anything other than US 51. Their county and city maps are terrible. One map that color codes US routes still has State St colored that way.
This leaves the possibility that US 51 is discontinuous in Jackson (from an MDOT maintenance point of view) and they have chosen not to sign the portion on State St anywhere that they still maintain to presumably discourage through traffic on it.
Of course there is no AASHTO action and the MDOT Commission doesn't seem to have prior meetings available on its website - only the current one. Annual reports exist but unless a project was done on the specific segment in question that won't be helpful. The state highway log which is not all that old also has no designation for this.
