Interstate 88, IL and NY??

[PurdueBill]

Page 5 of AASHTO guidelines includes this:

15. Any toll highway facility may be included in the U.S. Numbered System
when it meets all the criteria for inclusion, and when the request
for the marking originates with the official authority having
jurisdiction over the toll facility and the request is directed to
AASHTO and supported by the appropriate Member Department. The word
"Toll" shall appear over the official U.S. Route Marker and a toll-free
routing between the same termini shall continue to be retained and
marked as a part of the U.S. Numbered System.

ALT US 412 provides the free route in the US system vs. the Cherokee Turnpike.  If AASHTO wants to play hardball, a free ALT US 301 could be insisted on, or maybe DelDOT can get the toll to be for a "bridge" vs. the route in general.

[Duke87]

Also note how US 40 is concurrent with I-70 most of the way across Kansas, but then conspicuously leaves for local roads at the last free exit before I-70 enters the Kansas turnpike, only to re-enter I-70 at the first free entrance after the turnpike ends. This is the same "no tolls on US highways unless there is a signed free alternative" policy at play.

When part of what's now I-88 was "toll US 30", would I be correct in presuming that what is plain old US 30 today was signed as such then? If so, this would be consistent with the policy.

[SEWIGuy]

Also note how US 40 is concurrent with I-70 most of the way across Kansas, but then conspicuously leaves for local roads at the last free exit before I-70 enters the Kansas turnpike, only to re-enter I-70 at the first free entrance after the turnpike ends. This is the same "no tolls on US highways unless there is a signed free alternative" policy at play.

When part of what's now I-88 was "toll US 30", would I be correct in presuming that what is plain old US 30 today was signed as such then? If so, this would be consistent with the policy.

Yes US-30 was on basically the same route it is on now.  TOLL US-30 was signed as such only for a couple of years according to Rich Carlson's page.  It actually went along what is now I-88, south on I-294, south on IL-394 to reconnect back with US-30.