It's time to revive the northern half of I-840

[Daniel Fiddler]

Indeed.  From most to least utilized, the spokes are:

I-24 E, and it stays overcrowded all the way to I-75 in Chattanooga
I-65 N, and it stays overcrowded to the Kentucky line, where they've 6 lanes it
I-65 S, it's heavy until TN 96 Franklin, MAYBE Saturn Parkway, then it dies down a lot
I-40 E, it's heaviest to Lebanon, but stays busy all the way to I-81
I-40 W, it is really not that busy for local traffic past Charlotte Pike usually, mostly long-distance
I-24 W: almost no traffic, completely opposite of I-24 E

[sparker]

Indeed.  From most to least utilized, the spokes are:

I-24 E, and it stays overcrowded all the way to I-75 in Chattanooga
I-65 N, and it stays overcrowded to the Kentucky line, where they've 6 lanes it
I-65 S, it's heavy until TN 96 Franklin, MAYBE Saturn Parkway, then it dies down a lot
I-40 E, it's heaviest to Lebanon, but stays busy all the way to I-81
I-40 W, it is really not that busy for local traffic past Charlotte Pike usually, mostly long-distance
I-24 W: almost no traffic, completely opposite of I-24 E

Right.  The perennial issue with the underutilized I-24 corridor NW of Nashville is the fact that isn't part of a particularly useful commercial corridor to anywhere except St. Louis.  Chicago and environs, the "800-pound-gorilla" of commercial origin/destination points in the upper Midwest, really doesn't have a completely direct route to Chattanooga and, of course, Atlanta and Florida beyond that; the I-57/24 combination just adds too much mileage due to the lateral/E-W section in KY.  Truckers use I-65 because it's there and the "best of a bad lot" for that purpose -- and because of that, there's plenty of truck-related amenities situated along that corridor.  Venturing into the fictional realm for a second or two, an upgraded corridor more or less along US 41 via Terre Haute connecting I-69 and Evansville with either I-65 or I-57 near Chicago might, via I-69/169 in KY, provide such a direct connection; it would be a safe guess that the commercial traffic level on the aforementioned section of I-24 would increase dramatically.  Hell, truck tolls could even help pay for the I-69 Ohio River bridge project!   

[I-55]

The Northeast link would exist if the TN-109 speed limit wasn't set at 55. It should be 65 in most places.