As for US-50
Olney to Vincennes
O'Fallon to Caryle
Salem Bypass with I-57
are warranted due to volumes, industry, commuting or recreational.
Carlye to Salem and Salem to Olney are just too low to justify.
Last time I spoke with some folks in SE Illinois along US-50 in the 1960's they used to drive over to Vincennes for certain items not local.
They said in the 1980's it started to shift and more people drove to Effingham or Terre Haute.
That all changed somewhat when Wal Mart built their first, then replacement super center north of Olney.
Regional heath care referrals for many years went to south Evansville. Now they go north to C-U via Carle.
The local oil business moved to Robinson (Marathon Refinery) when the Lawrenceville Indian Refinery closed down. That refinery had a lot of workers from Olney and Vincennes.
Robinson also has a large Hershey's plant there (the original Heath Bar factory).
Some people drive to work the Duke Energy plant across the Wabash near Mt Carmel or the CIPS Power Plant between Olney and Newton.
I know its hard to believe, but the Vincennes-Lawrenceville International Airport (just off US-50) used to have regularly scheduled airline service. Piedmont used to run commuter service out of there to either Indy to Evansville. It was to support all of the oil executives and employees flying in and out the 2 refineries (Robinson & Lawrenceville) nearby.
For those who are into deep trivia, "Havoline" oil was produced at the Indian Oil Refinery in Lawrenceville from 1906-1962. It's also where multi-grade oil was invented. It was sold to Texas Oil (Texaco) and the Indian name was retired. (But the town mascot is still the "Indians")
For many locals, they believe the political influence of the area declined as the local oil industry waned. The Indian refinery was finally sold to Marathon, and then shut down due to it being obsolete and uneconomic.
There is still oil in the region, but it is difficult to locate and extract. However, much of the remaining oil can be removed via fracking, but ILEPA created such overly strict environmental laws it remains uneconomic. While Illinois continues to lower taxes on high sulphur coal, opportunities for extracting oil and gas sit on the shelf. If cheaper fracking options remain in the Bakken or Permian Basins, the SE Illinois oil will probably remain in the ground.