The Nexus group webpage bringing together our ongoing and completed research on the I-35W Bridge collapse is available here. Evaluation of the Transportation Effects of the I-35W Collapse
Note in particular, several reports (links near the bottom of the page) which document the effects of the bridge collapse, reproduced here:

Zhu, S, D. Levinson, H. Liu, and K. Harder (2008) The traffic and behavioral effects of the I-35W Mississippi River bridge collapse (under review)

Xie, F. and D. Levinson (2008) Evaluating the Effects of I-35W Bridge Collapse on Road-Users in the Twin Cities Metropolitan Region (under review)

He, Xiaozheng, Saif Jabari, and Henry X. Liu (2008) Modeling Day-to-day Trip Choice Evolution under Network Disruption (under review)