I remember us talking about the Iowa law at that meet. It disgusts me that they would have basically nixed the renumbering idea instead of having a reasonable discussion with Illinois DOT and Iowa DOT on the matter.
I seem to remember that it did start out with the two DOTs talking. I think some of the concern with why to do it was how many accidents there were each year at the Big X (the I-80/I-74/I-280 interchange) and to a lesser extent the Big Y (I-80/I-280). Proposals for lettered suffixes were dismissed in that those had been done away with in the 1970's. There were also concerns about the I-280 section flooding and being closed in places every few years and not wanting to send all of the would be I-80 traffic over current I-74 through town when that happened. When the I-80 eastbound bridge closed for repair concerns, I heard about people taking 3-4 hours to get from I-80 to I-280 through town on I-74 the first day which in part was due to one lane on the I-74 bridge being closed in addition to all the extra traffic.
So it started out being somewhat rational discussion. Then somebody spouted off that Iowa needed to hurry up and agree to the changes so that businesses could move to Illinois in order to stay on I-80 and bring the sales, gas, hotel, and income tax revenue to Illinois. After that, the law was quickly put into place as politicians were motivated.
After renumbering ideas were nixed, both DOTs agreed to have engineers evaluate the interchanges and suggest safety improvements. Some of the ramps ended up being lengthened, widened, and banked differently. Those changes decreased the number of cars sliding off the ramps in the rain, snow, and ice as well as reducing the number of semis that tipped over. So in the end the rationality of looking into and fixing some problems with the interchanges for safety did happen.