In Chicago, L3 appears to be routing some traffic to UU directly, but for some other UU destinations, L3 is handing-off to UU via New York:
trace from L3/Chi to 209.98.0.2 (AS8015 via 701) is carried to UU via New York (edited):
1 ae-1-53.bbr1.Chicago1.Level3.net (4.68.101.65) 8 msec
2 as-4-0.bbr2.NewYork1.Level3.net (64.159.0.238) 20 msec
4 mci-level3-te-newyork1.Level3.net (4.68.110.234) 20 msec
8 visi-gw.customer.ALTER.NET (157.130.98.2) [AS701 {ALTERNET}] 32 msec
Oddly, a L3/Chi trace to the last hop above within AS701 (157.130.98.2) enters UU immediately in Chicago, taking the shorter path to Minneapolis:
1 ge-7-0-0-56.edge1.Chicago1.Level3.net (4.68.101.173) 0 msec
2 0.so-0-3-0.BR2.CHI13.ALTER.NET (204.255.168.117) [AS701 {ALTERNET}] 0 msec
6 visi-gw.customer.ALTER.NET (157.130.98.2) [AS701 {ALTERNET}] 8 msec
UU support has verified that AS8015 prefixes are advertised at UU's L3/Chi peering point; and L3 support reports this is "routing as designed". I would guess that UU requires its peers to use hot-potato routing, so I'm at a loss as to what kind of traffic engineering is being used.