It was soundbound I-35W, just south of 28th street, where the road makes a slight bend to the left and the road starts sloping down toward the river, there's the long bridge over the RR tracks, near Long Ave and 33rd street. It looks like a passing shower from west to east dropped some freezing rain there immediately before the accident which explains why no southbounder had any warning of a slick road condition. It looks to have been a near perfect trap.

As I understand it, NTTA is responsible for their toll lanes maintenance, I don't know if NTTA pre treated the road or not, I'm sure TxDot did their portion. in the pic you can see the concrete paving portion denoting the bridge vs. the asphalt at grade level. The river is just south of the pic.

Several years ago we passed through a front while traveling south on 287, went from cool and dry to warm and humid, in just a second every window in the truck was fogged to opaque. 75 MPH with no warning to no vision was kinda scary. NO warning at all, similar to what happened on the bridge. 2¢

~ 12 to 15 seconds you can see the pileup at the south end of the bridge.