I-35W Bridge (Minneapolis)

by Christel Kellar, 3 October 2021 | Comments

Video source: Fox 9 KMSP

On August 1, 2007, the I-35W bridge that crossed the Mississippi River near downtown Minneapolis collapsed shortly after 6:00 PM during rush hour traffic. The collapse resulted in 13 deaths and 145 injuries. There were 111 vehicles involved, with 17 of them having to be recovered from the river. The bridge was under construction at the time of the collapse. The National Transportation Safety Board (NTSB) concluded one of the factors of the collapse was due to the gusset plates being too thin. The plates were only a half inch thick and should have been one inch thick (NTSB).

Image source: NTSB

I-35W Bridge Background

  • 1964 - I-35W bridge construction begins
  • 1967 - I-35W bridge opens
  • 1977 - Construction project increased the thickness of concrete on the deck that added 13.4% of dead load
  • 1998 - Construction project that included median barrier, traffic railing upgrades and an anti-icing system which increased the dead load by 6.1%
  • 2007 - Construction began in June for adding a 2” concrete overlay

Bridge inspections were done and recorded on an annual basis. An inspection report in 1993 noted issues with the gusset plates (corrosion). Independent fatigue assessment by the University of Minnesota in 1999 did not include inspection of the gusset plates and a fatigue evaluation by URS in 2003 did not calculate the capacity of the gusset plates. During the NTSB investigation, inspection photos from 1998 and 2003 showed bowing in some of the gusset plates. Interestingly enough the bowing was not documented in any of the state inspection reports (NTSB).

The New Bridge

The funding request and approval process happened quickly. A timeline of the events are as follows:

  • August 23, 2007 - MnDOT releases a request for a proposal for a new bridge
  • September 14, 2007 - MnDot gets 4 technical proposals
  • September 18, 2007 - MnDot receives financial proposals
  • October 5, 2007 - MnDOT awards the contract
  • October 15, 2007 - Transportation Contingency Advisory Group gives MnDOT permission to spend an additional $60 million through February 2008. MnDOT had requested $195 million.
  • October 16, 2007 - MnDOT sued over bid selection
  • October 31, 2007 - judge rejects order to halt constructions
  • November 1, 2007 - construction begins
  • September 18, 2008 - new bridge opens

The I-35W bridge replacement project was not the first of its kind to be accelerated. There have been other bridge projects that have been sped along after natural disasters such as earthquakes and hurricanes. The typical review process for drawing and calculation review is 30-45 days (MPR, 2007).

The I-35W project was awarded to Flatiron Constructors who had placed a bid for $234 million and said they would be able to complete construction in 437 days (MPR, 2007/09/19). The bridge was completed months ahead of schedule and the contractor received a $200,000/day bonus (Streets, Part 7).

Image source: America's Transportation Awards

Public Finance and Infrastructure

The original I-35W bridge that collapsed had been constructed using 90% federal funds and 10% state funds. The new bridge that was constructed at a cost of $251 million was 100% federal funds (Streets, Part 7). According to Irene Rubin’s text, in the 3 years prior to the bridge collapse, Minnesota legislators had diverted 50% of bridge funding away from bridge repair and maintenance (Rubin, pg 164). In May of 2007, Minnesota Governor Tim Pawlenty vetoed gas tax increases by the legislature. Those funds would have been used for bridge inspections. Governor Pawlenty had campaigned on a “no new taxes” pledge (Streets, Part 4). The original I-35W bridge was listed as structurally deficient as early as 1990. The bridge inspection report from 2006 gave the bridge a sufficiency rating of 50. This would have allowed the bridge to be replacement under the Highway Bridge Program, of which 90% of the funds would have been from the federal government since it was part of the interstate highway system (House Report).

David Levinson wrote an eight part series about the I-35W bridge in 2012 (7 years after the collapse). In one of his articles he said: “We need to address the question of the appropriate role of politics in infrastructure decisions.” I think this is a critical point. Projects are proposed and rated to determine what gets done. Mr. Levinson went on to say: “...we should spend our money more carefully, taking care of the existing systems and users first, and engaging in graceful abandonments as necessary, but not building new infrastructure which will require long-term maintenance without any means for doing so.” (Streets, Part 8). I could not agree with him more.

In one of his prior articles, Mr. Levinson states: “The political problem is deeper than just the fate of a few politicians though. It is a classic problem in transportation funding. Ribbon cuttings on new projects are much more attractive to politicians (and newspapers and TV news) than maintaining what we have.” (Streets, Part 4). This seems to be an important aspect in how funds are utilized. Citizens want to see that their money (taxes) are being put to good use. Citizens have no visual confirmation of fund usage for road and bridge maintenance and repair. They are on the other hand, able to see new roads and bridges. Politicians may use this as justification to build, rather than maintain. Unfortunately, that could result in more accidents due to structure failure.


There were successes that came of this unfortunate event: 1) all state bridge inspections in Minnesota were accelerated and completed by December 2007, 2) review all all gusset plates on the 25 truss bridges in the state system was completed, 3) Minnesota increased the number of inspectors and added more snooper vehicles to be used during bridge inspections, 4) Minnesota revised its policy regarding placement of construction loads on bridges (NTSB), and 5) Minnesota was able to pass a gas tax increase (Streets, Part 4).

Lessons Learned

Bridges are expected to last 75-100 years (USDOT). The fact that the I-35W bridge only made it 40 years (about half of what could be the expected lifespan of a bridge) provides clear evidence that there were issues with the bridge, whether that be design or construction. Per our group bridge expert, Michael Hill, it is likely that when the bridge was originally built, it only had a 50 year lifespan. Even if it truly had a 50 year lifespan, it still fell 10 years short of that mark.

While it is important that bridges are rebuilt as quickly as possible after a natural disaster, it is also imperative that processes and procedures for proposals, bidding, and selection are followed. Plans will need to go under the usual plan review to ensure that the proposal specifications are met and adhered to, and that any construction design defects that could affect the integrity of the structure are found and corrected. Politicians responsible for making project funding decisions must keep in mind the importance of inspecting, maintaining, and repairing current infrastructure, even though it may not be as sexy as a new road or bridge. Those that fail to remember this important fact will likely have a quick end to their political career if an event such as the one described occurs while they are in office.

Image source: streets.mn

Annotated Bibliography

Gee, K. and Henderson, G. (2007, October 23). Hearing on Highway Bridge Inspections. US Department of Transportation. https://www.transportation.gov/testimony/highway-bridge-inspections.

This article included testimony provided by two key personnel with the US Department of Transportation to the Committee on Transportation and Infrastructure Subcommittee on Highways and Transit of the US House of Representatives. It provides information regarding the reason the bridge inspection program was started, the frequency of bridge inspections, 5 different types of bridge inspections, and bridge inspection ratings.

House of Representatives. (2008, July 10). National Highway Bridge Reconstruction and Inspection Act of 2007. House Report 110-750. https://www.govinfo.gov/content/pkg/CRPT-110hrpt750/html/CRPT-110hrpt750.htm.

This source was a report to the House of Representatives that outlined the events of August 1, 2007 involving the I-35W bridge collapse in Minneapolis, MN. It also included a history of the bridge inspection program; the year it started, the reason it was started, the required frequency of inspections, and the different types of inspections.

Levinson, David. (2012, July 28). The Fall and Rise of the I-35W Mississippi River Bridge - Part 4: Politics. Streets MN blog. https://streets.mn/2012/07/28/the-fall-and-rise-of-the-i-35w-mississippi-river-bridge-part-4-politics/.

Mr. Levinson wrote an 8 part series of short articles about the I-35W bridge in Minneapolis. This piece discussed the recent history of gas taxes in the state of Minnesota. The news in Minnesota in May of 2007 was that Governor Pawlenty vetoed the gas tax increase bill that had been approved by the legislature. The increased funds were to be directed to bridge inspections.

Levinson, David. (2012, July 31). The Fall and Rise of the I-35W Mississippi River Bridge - Part 7: Replacement. Streets MN blog. https://streets.mn/2012/07/31/the-fall-and-rise-of-the-i-35w-mississippi-river-bridge-part-7-replacement/.

This was another of Mr. Levinson's articles that he wrote dissecting the I-35W Bridge. This article focused on the cost of replacing the bridge as well as some additional features that should have been considered during the construction phase. The contractor completed construction early and received a bonus for each day it finished ahead of schedule. This article includes that daily amount of of $200,000.

Levinson, David. (2012, August 1). The Fall and Rise of the I-35 Mississippi RIver Bridge - Part 8: Policy Implications. Streets MN blog. https://streets.mn/2012/07/31/the-fall-and-rise-of-the-i-35w-mississippi-river-bridge-part-7-replacement/.

The final article in Mr. Levinson's series discusses the impacts of the bridge collapse in the state of Minnesota. Bridge repairs were accelerated as a result of the collapse. 

Minnesota Legislature. (2020, October). Minneapolis I35W Bridge Collapse. Minnesota Legislative Research Library. https://www.lrl.mn.gov/guides/guides?issue=bridges.

This is a record of the events of the bridge collapse. The article includes important dates from August 1, 2007 (the date of the collapse) through August 1, 2011 when the bridge remembrance garden was unveiled by Governor Mark Dayton and Minneapolis mayor R.T. Rybak.

National Traffic Safety Board. (2008, November 14). Collapse of I-35W Bridge. Minneapolis, Minnesota. August 1, 2007. National Transportation Board. https://www.ntsb.gov/investigations/AccidentReports/Reports/HAR0803.pdf.

This piece is a 178 page document that is the final report from the NTSB in regards to the I-35W bridge collapse. It provides great detail as to the events on the day of the collapse, which included information on the equipment and materials being used for the construction project that was currently in progress on the bridge. This information also indicated where the equipment and materials were located on the bridge.

Rubin, I. (2020). The Politics of Public Budgeting. Getting and Spending, Borrowing and Balancing. 9th Edition. Sage. Thousand Oaks, CA.

This is a graduate level textbook that focuses on public budget and finance topics. 

Sheck, T. (2007, August 15.) Other States’ Experiences Inform Debate Over Bridge Rebuild Timeline. Minnesota Public Radio. https://www.mprnews.org/story/2007/08/15/transport.

This article was a summary of a hearing of the joint house and senate transportation committee.  There was concern by some attendees over the accelerated timeline for replacing the bridge. The article included examples of other bridge projects that had been completed at a fast pace due to damage sustained during a natural disaster such as a hurricane or earthquake.

Scheck, T. (2007, September 19). Rich Contract Awarded for I-35W Bridge Replacement. Minnesota Public Radio. https://www.mprnews.org/story/2007/09/19/bridgebids.

This piece includes information about the contractor that won the bid for the bridge replacement project, their estimated cost, and their timeline. The article included a list of the other contracting companies that submitted bid proposals.