I get that it's the junction of I-35 and I-90, but by that logic, should Austin not be a control city for I-90? Owatonna has a larger population than Albert Lea and much more infrastructure along the freeway. I-35 also meets two U.S. highways (14 and 218) in Owatonna, where I-90 only meets one (218) in Austin. What was MN/DOT's logic behind this?
Because it's the junction of I-35 and I-90. Neither Austin nor Owatonna is the junction of two Interstates, hence they aren't control cities.
Austin is a control city! http://goo.gl/maps/04bo5
Oh. The phrasing 'should x not be y' usually implies that x is not y and you're asking if it should be.
AASHTO (http://home.roadrunner.com/~pwolf/controlcities.html) doesn't list Austin, so maybe it was a recent change. (It's not one-off; I see it on the ramp from US 52.)
Austin is not a "primary" control city, it is a secondary one. Secondary control cities show up most often at a regular interchange (non Interstate to Interstate) instead of a major junction interchange. Think of it like how Janesville and Beloit are secondary to Chicago on I-90 Eastbound at the I-39/90/94/Wis 30 Badger Interchange or I-55 in Illinois heading north from St Louis. Springfield, Lincoln, Bloomington, and Joliet are all secondary to Chicago and they only show up as control cities at less important junctions.
Maybe they just wanted to put something between Sioux Falls and La Crosse.
EDIT: Oops, misread title and posts and thought we were talking about I-90. Point still stands though, just swap MSP and DSM in for the I-90 controls I mentioned.
It's also the control city for I-90 east at Sioux Falls.