Unlike bridges, transportation networks are seldom “fracture critical”. While the Interstate Highway System did what it could to sever local streets and channelize traffic onto fewer, larger, limited access link to achieve economies of scale and higher speeds and throughputs and the expense of redundancy, there was enough remaining redundancy to ensure that this one bridge collapse would not have devastating transportation implications. Had the I-94 bridge collapsed instead, I am sure the consequences would have been much worse, as the alternative paths are not as convenient. But again, the Twin Cities would have muddled through.

Several lessons can be drawn. If there is redundancy, maintaining road operations during construction may not be necessary, and may needlessly delay construction while exploding its cost. There have been projects, in Minnesota notably Mn36, where closing the road entirely to speed construction has been successful. Rebuilding a bridge while keeping it open is like doing brain surgery on one-self. In principle it is possible, but why? The length of bridge construction in other examples (e.g. the Oakland Bay Bridge, admittedly a somewhat more complicated project)
versus the less than one year from design to opening that this bridge took is instructive.

Actual effects were much less than forecast. People are quite adaptable in their travel patterns, especially if there are alternatives routes and destinations.

As a consequence of the Bridge collapse, many other bridges were repaired more quickly than they otherwise would have been. A list of recent Bridge closures in the region below is illustrative.

1. August 1, 2007: I-35W
2. January 2008 Hastings Bridge
3. March 20, 2008 St. Cloud Bridge
4. March 26, 2008 University of Minnesota Pedestrian Bridge
5. April 25, 2008 Lowry Avenue
6. May 6, 2008 Blatnik Bridge (I-535) in Duluth
7. June 4, 2008 MnDOT barricades Hwy. 43 bridge over Mississippi River at Winona

Three Successes

• Emergency Response
• Immediate Traffic Restoration
• Quick Completion of Bridge with Design/Build

Three Failures

• Bridge Collapse
• Removal of Successful, Low Cost Restoration Measures
• Overpaying for Bridge

Overall, Americans seem good at short-term tactics but poor at longer term strategy. This needs to be rectified. While there were positive outcomes, including the passage of the gas tax, and increased attention to maintenance, there may have been some over-reaction in terms of replacement of bridges.

While there was some accountability, some key personnel remained in place. Firings and resignations need to be used more often in the aftermath of events like this, some people should assume responsibility.

We need to address the question of the appropriate role of politics in infrastructure decisions. We don’t expect politicians to make recommendations about which electric power cables are replaced, why are they so involved in maintaining existing roads. (The construction of new roads is on the other hand, more obviously political in nature). Should Mn/DOT and other similar agencies move toward a public utility model to de-politicize?

We are not good at dealing with low probability, high consequence decisions. We are not good at assessing the value of either.

Unless something is done, failure will be more frequent, the Interstate system is aging and nearing the end of useful life for many components.

In The Transportation Experience, we identify a set of strategies for maturity:

• Abandonment
• Cash cow – using resources for something else
• Maintenance and Rehabilitation
• Replacement

Abandonment of the Interstate system as a whole seems premature, and while a handful of selected urban links have been closed, these are very much the exception. The Cash cow strategy is in fact what has been employed for the past several decades, as the gains from the built infrastructure exceeded by far the amount that was reinvested in it. This is of course economically correct, infrastructure should be fully exploited to its capacity. But this needs to be coupled with appropriate levels of maintenance and rehabilitation, and ultimately planned replacement, otherwise the goose that lays the golden egg will die.

The “Weak Bridge” sign that one sees all over England is not terribly reassuring, and indicates an unwillingness to recapitalize the network. In the US context, there should be more money for transportation maintenance and rehabilitation, we are eroding our physical capital. If there isn’t … 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. The mantra Fix it first has been suggested for this strategy, and I agree. Unless something is done, the problem of decaying infrastructure will only get worse (the physical world being subject to entropy and all), bridges do not repair themselves.

Other Parts in Series: Part 1 – Introduction, Part 2 – Structure, Part 3 – Communication,Part 4 – Politics, Part 5 – Economics, Part 6 – Traffic, Part 7 – Replacement, Part 8 – Policy Implications

The replacement bridge cost $251 million, funded almost entirely by federal government. We can debate whether the federal government should have paid for it (it was originally built with 90 percent federal contributions, 10 percent state, but matches recently are much more balanced), since most traffic using the Bridge both originated in and is destined for Minnesota. With Minnesota Congressman James Oberstar then Chair of the House Transportation Committee, there was plenty of political support behind this.

The replacement bridge was hurried, completed by September 2008, several months ahead of the original schedule. This is good, a lack of a bridge costs the economy. (Xie and Levinson estimated between $127,000 and $170,000 per day, MnDOT estimated $400,000 per day). The contractor received $200,000 per day bonus for early completion. So perhaps in an economic sense, too much was paid to complete it a few months early.

Rebuilding a collapsed bridge is of course a crisis, but it is also an opportunity to do something interesting. Rushing designs may mean that ideas are missed. What was built is a functional bridge, and there are state-of-the-art real-time structural health monitoring systems installed, so I have no fear driving over it. It was also ensured that the Bridge would be compatible with any future light-rail transit lines, though none are planned for this bridge (and how they would transition from the center of the Bridge to any reasonable destination is extremely unclear). But could more have been done?

The snow removal and icing problem was not considered. Minnesota is famous for its winters. The previous I-35W bridge had installed a de-icing system (in response to earlier crashes), which had been speculated to be responsible for corrosion of the structure. While the NTSB did not find that, de-icing chemicals do have environmental consequences.

A solution not considered was air rights. A bridge over the Mississippi is expensive. But imagine having a 2 or 3 story office building hanging from below, and/or built above the highway. The views from the River are fantastic. It will not impair other views of the river especially much, and would generate a significant amount of revenue to pay for reconstruction. One example would be the historic London Bridge, which had houses and stores along the side, encroaching on travelways. There are better ways to combine transportation arteries with development opportunities, and creative design can show the way.

Why did we not build a habitable structure above the road deck, so that offices, residences, hotels, etc. could share the view? It would have increased the profile of the Bridge by two stories, but created an enormous amount of leasable space, leases which could have paid for themselves and the Bridge. Obviously it would increase the initial construction cost, and perhaps time, but that would be amply repaid over the long-term. That structure would further have shielded the roadway from ice and snow, reducing road snow clearance costs and crashes.

The bridge opened in the early darkness of September 18, 2008. A parade of first responders, and then a bulge of traffic all hoping to be the first (and none succeeding) went across. Soon the Bridge was attracting 120,000 vehicles per day, measurably off the pre-collapse levels.

Other Parts in Series: Part 1 – Introduction, Part 2 – Structure, Part 3 – Communication, Part 4 – Politics, Part 5 – Economics, Part 6 – Traffic, Part 7 – Replacement, Part 8 – Policy Implications

Travel behavior changes after network disruption as well as after the replacement of disrupted links are not well-understood. The first table shows the number of river crossing trips by type of facility before and after the collapse and the reopening.

We discover 46,000 lost trips daily after the collapse (nearly a third of what the I-35W Bridge had carried), and 20,000 found trips after the new bridge opened. Those lost trips may not have been made, or more likely, found different destinations not requiring a river crossing. This provides additional evidence to the phenomenon of induced demand.

Gains from the Bridge for three peak periods re-estimated with accurate (observed) travel times (but fixed and not-observed OD matrix), shown in the second Table, were on the order of $70,000 per day (somewhat below our initial low all-day estimates ($127,000), far below Mn/DOT’s, and also below the contractor early completion bonus). Much of that gain is lost once the I-94 bridge lane disappears, as consistent with the original results. $42,000 annualizes to about $15 million in benefit, for a $250 million dollar bridge (which pays off in about 23 years at 3% interest). The I-94 lane restriping paid off in a matter of a month.

Other Parts in Series: Part 1 – Introduction, Part 2 – Structure, Part 3 – Communication, Part 4 – Politics, Part 5 – Economics, Part 6 – Traffic, Part 7 – Replacement, Part 8 – Policy Implications

At the request of Mn/DOT, shortly after the collapse, Feng Xie and I estimated the Twin Cities 7-county region daily vehicle hours of travel with and without the Bridge using a planning model under two assumptions. The first kept the trip table fixed. This means that people did not change the number of trips, or destinations, in response to the Bridge failure. This should give an upper bound to the effects of the Bridge failure. The second allowed trip destinations to vary (though keeping the number of trips fixed). This provides more of a lower bound of the effects. Clearly some people can switch destinations, or avoid trips altogether, if the cost of their previous destinations are now too high. On the other hand, not everyone can do so. The exact number of people who change destinations is not something we can easily know.

Note, these are direct model outputs, so while the precision is high, the accuracy is not nearly as high as implied by the precision. We monetize these numbers using values of time from MnDOT (The current MnDOT values of time can be found here, a the time the values given were Auto $12.63/hour and Truck $20.41 and we assumed 80 percent auto and 20 percent truck giving a composite value of time of $14.19).

I believe the OIM Value of Time for Trucks is very low, our estimates (Smalkoski, Brian, and David Levinson (2005) Value of Time for Commercial Vehicle Operators. Journal of the Transportation Research Forum. 44:1 89-102.) put the number at closer to $50 per hour. If we used that, we would get a composite value of time of $20.14.

The results in Table below are of course estimates. However, the number is large and positive, which we expect. And the numbers lead us to conclude that letting bridges fall down is bad public policy. Which most of us already knew. The number does have uses aside from (rhetorically) beating people over the head, it tells us, for instance, how much we should reward contractors for early completion.

The problem is that those who benefit from the Bridge (or lose from the absence of the Bridge) differ from those who pay for it, and are responsible for maintaining it. If presented with the choice of paying and keeping the Bridge up and not paying and letting it fall, most users would have gladly paid more than was required to keep the Bridge up.

We conducted a more thorough analysis later (Xie, Feng and David Levinson (2008)Evaluating the Effects of I-35W Bridge Collapse on Road-Users in the Twin Cities Metropolitan Region. Transportation Planning and Technology 34(7) pp. 691-703.), considering upgrades to alternative routes, such as restriping I-94 to add a lane and upgrading Mn280, with somewhat lower results.

Other Parts in Series: Part 1 – Introduction, Part 2 – Structure, Part 3 – Communication, Part 4 – Politics, Part 5 – Economics, Part 6 – Traffic, Part 7 – Replacement, Part 8 – Policy Implications

Some will say the Bridge collapse was not about money. Throwing money at the Bridge would not have kept it from falling. Others note money could have bought:

• more inspections,
• a structural (e.g. finite-element) model of the Bridge,
• better, faster repairs,
• the ability to replace the Bridge sooner.

Money could have been spent more wisely. More importantly, money is always a constraint on decision-making at MnDOT. As was noted in the Star Tribune: “Phone call put brakes on bridge repair: Plans to reinforce the Bridge were well underway when the project came to a screeching halt in January amid concerns about safety and cost.” (Article by Tony Kennedy and Paul McEnroe, Star Tribune staff writers Last update: August 18, 2007 – 4:36 PM)

Tim Pawlenty had already vetoed a legislature-passed increase in the gas tax that could have raised money to repair bridges like this one. The latest vetoed gas tax would not have solved this problem, but previous taxes that were not passed (due in part to Pawlenty’s previous veto threat) may have, had the money been spent on this kind of thing. The gas tax had not been raised in Minnesota since 1988, and thus its purchasing power had diminished significantly, while the network was expanded and aged, and traffic levels increased. Pawlenty’s campaign took pride in this veto, posting a clipping from the Star Tribune on their website:

“WEDNESDAY, MAY 16, 2007
STAR TRIBUNE: Pawlenty vetoes gas tax, income tax bills

By Patricia Lopez, Star Tribune — Gov. Tim Pawlenty struck swiftly and with strong language Tuesday to veto a gasoline tax increase and an income-tax-for-property-tax swap that were at the heart of the DFL’s agenda for the session. — DFLers accused him of protecting the state’s richest 1 percent — those who would have borne most of the income tax increase, which would pay for the proposed property tax relief — at the expense of everyone else. But they conceded that some of their top objectives are fast sliding out of reach.”
—
PREPARED BY PAWLENTY FOR GOVERNOR –
PO BOX 21887 – EAGAN, MN 55121. (This article can still be accessed. Accessed April 19, 2012)

Gas Taxes in the United States and Minnesota are dedicated to transportation (and in some cases just to roads). The 2008 Minnesota gas tax bill phased in an increase of the gas tax by 8 1/2 cents a gallon by 2014. Of that, 3 1/2 cents of the gas tax increase was dedicated to paying the debt service on $2 billion in road and bridge bonds. The bill borrowed $1 billion from 2009-2010, with $600 million earmarked for repairing or replacing the state’s 13 most dangerous bridges. In addition, the bill increased the sales tax in the seven-county metro area by 0.25 percent for transit. It also increased license tab fees on newly purchased cars and trucks (1.25 percent on sale of new cars, drops 10 percent per year).

The bill was passed by the legislature, but vetoed by Governor Tim Pawlenty. The Governor had run on a “no new taxes” pledge, and clearly had political aspirations. He was frequently mentioned as a possible Vice Presidential running mate for the 2008 GOP Presidential Nominee, John McCain, and was hosting the GOP convention in St. Paul, Minnesota that year. While in the event, the Governor of Alaska, who had more foreign policy experience, got the nod as the VP candidate, Pawlenty continued to look towards higher office, and was for a time, a candidate in the 2012 GOP party nominating process, before dropping out for lack of support and will.

The Override Six are Republicans who voted with DFL to override Gov. Pawlenty’s veto of the gas tax bill. Four of them lost their seats due to Primary challenges, while the Republicans lost two of those seats to the DFL in the 2008 General Election. This leads to the rule that voting in favor of a gas tax increase can be dangerous to your political health, if you are a Republican.

• Representative (District) – Party Endorsement? – Primary Victor – General Election Victor
• Bud Heidgerken (13A-Freeport) – retired – – Paul Anderson (R)
• Rod Hamilton (22B-Mountain Lake) – Rod Hamilton – Rod Hamilton – Rod Hamilton (R)
• Ron Erhardt (41A-Edina) – Keith Downley – Keith Downley – Keith Downley (R)
• Neil Peterson (41B-Bloomington) – Jan Schneider – Jan Schneider – Paul Rosenthal (DFL)
• Jim Abeler (48B-Anoka)- no endorsement – Jim Abeler – Jim Abeler (R)
• Kathy Tingelstad (49B-Andover) – retired – – Jerry Newton (DFL)

Carol Molnau was the state’s Lieutenant Governor and the MnDOT Commissioner. While she had been confirmed in the first Pawlenty Administration, when she was reappointed, the DFL legislature did not confirm her, and her appointment expired in February 2008. That can be directly tied with dissatisfaction with her and the Governor’s performance dealing with the Bridge. Notably she was not the Department’s point person with the media in days, weeks, and months following the collapse. She was replaced by Tom Sorel, a federal civil servant who had worked on the Bridge replacement process.

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. People are also more interested in road surface than the underlying structure. Yet pavement failure, while bad, is not nearly as bad as structural failure. “Failure” in the traffic level of service sense (LOS “F”), while economically costly and personally annoying, and perhaps leading to more (or at least different) crashes, does not have anywhere near the same connotation as structural collapse.

The competing uses of funds are ultimately political decisions. Should money be spent for bread and circuses (er. football and baseball stadiums) rather than genuinely productive infrastructure? Five years later, should money be spent on new bridges with added capacity (e.g. the Saint Croix River Crossing in Stillwater) while over 1000 structurally deficient bridges remain in Minnesota (Kimball, Joe (2011) MinnPost, Report says 1,149 Minnesota bridges are deficient)?

Other Parts in Series: Part 1 – Introduction, Part 2 – Structure, Part 3 – Communication, Part 4 – Politics, Part 5 – Economics, Part 6 – Traffic, Part 7 – Replacement, Part 8 – Policy Implications

Yet the news traveled fast. TV, radio, on-road variable message signs, phone calls, emails, all helped transmit this knowledge. We have evidence on how the news traveled by looking at traffic counts. The figure below shows the difference in counts between August 1 and a week earlier, July 25, which are otherwise similar days. As noted, behavior changed quickly that night, traffic counts were lower systemwide, but especially upstream and downstream of the collapse. In contrast the best long distance alternatives (Mn100 and I-35E saw upticks in traffic).

Other Parts in Series: Part 1 – Introduction, Part 2 – Structure, Part 3 – Communication, Part 4 – Politics, Part 5 – Economics, Part 6 – Traffic, Part 7 – Replacement, Part 8 – Policy Implications