Mississippi

[froggie]

Does anyone here know why the I-59-MS 42 interchange is the way it is?

The footprint of the interchange is huge, and they demolished some buildings to make way for it. There's a third bay under the bridge for a southbound CD to serve the existing loop plus a future loop for southbound 59-to-eastbound 42 traffic. The advantage of this two-adjacent-loop layout is that it eliminates the need for a traffic signal on the west side of the interchange. However, they still built the ramps on that side to intersect perpendicularly with 42, which you'd do only if the intention was for traffic to turn left there. Indeed, there's a left turn pocket striped there now even though it's redundant.

If MS 42 was extended to the northwest, it could serve as an extension of the US 49 Hattiesburg bypass, but the extra ramps don't seem helpful for traffic headed along that route.

Also, while I mentioned the third bridge span to accommodate a future CD road, the existing loop ramp would have to be almost completely reconstructed to tie into the CD and pass through the span. See what I mean?

I'd appreciate any insight y'all cound provide.

Dating back at least to when I was stationed in Mississippi the FIRST time (so talking 25 years ago now), there were two considerations being made for extending a roadway west of that interchange.  One was as a new alignment freeway for an occasionally-proposed "Jackson-Gulf Coast Interstate", in order to avoid heavy development along the US 49/MS 42 concurrency.

The second consideration was to extend such a road as part of a beltway around the Hattiesburg area.  This is still being considered as part of the MPO's transportation plan.

I want to say I saw early schematics of an "ultimate configuration" of a cloverleaf for the I-69/MS 42 interchange...this would certainly explain why it's so wide on the west side and the frontage road was built farther out in the southeast corner.

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Speaking of the Hattiesburg area, I found this news piece from last fall that MDOT is considering converting the I-59/US 11 interchange at Exit 60 into a diverging diamond.