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.
- August 1, 2007: I-35W
- January 2008 Hastings Bridge
- March 20, 2008 St. Cloud Bridge
- March 26, 2008 University of Minnesota Pedestrian Bridge
- April 25, 2008 Lowry Avenue
- May 6, 2008 Blatnik Bridge (I-535) in Duluth
- 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