US-30 is a slow stop and go crawl through the industrial cities of northern Indiana and the large suburbs south of Chicago. I-80 is a multi-lane superhighway through the same area, and it carries extremely heavy traffic, particularly where I-80, I-90 and I-94 are sharing the same road in NE Illinois.
If you hit I-80 at the wrong time, e.g. they are trying to clear away a wreck, it can be a dead stop and long wait. If you hit it at the right time, you might sail through at 50-60 mph, but it does get hectic with fast drivers cutting in and out of any open sections they find. You'll never make 50 mph going across US-30, you would be very lucky to average 30 mph from I-65 to Joliet.
Neither route goes through Chicago, both cross well south of the city, but there are lots of old industrial cities and bedroom communities that close.
First US-numbered highway to cross well south of Chicago is US-24, but even that has frequent small towns with very slow (as low as 20 mph) speed limits and some congested areas of its own. It is also one of the diagonal routes, running southwest from Detroit through Fort Wayne towards Kansas City before becoming a more east-west route in Kansas and Colorado.
I've used the state highways, 10 in Indiana, 114 and 17 in Illinois, to cross Indiana and Illinois south of the congestion.
But what is the better alternative depends on the longer route, from where to where, because if you are trying to get across the bottom of Lake Michigan and then directly west or northwest, a route well south of Chicago takes you a long way (and a long time) out of your way. But if you are going from Toledo toward the southwest, US-24 is a good start, until you connect with an Interstate to take you south more quickly (like I-57 + I-74, or I-55 to I-70).
Tom Test
Itasca Spirit 29B
