August 2007 Archives

From CBC (via Zvi) Montreal mayor wants inspection reports for private buildings. It seems our neighbor to the north has crumbling infrastructure too. This is somehow reassuring (if it can happen to Canada it can happen anywhere, so it's not anything "we" did or didn't do), on the other hand it suggests there is no easy example to point to, if only we did like "so and so" we wouldn't have these problems.

Awareness of crumbling infrastructure is like a virus (whether the infrastructure itself is crumbling because of some contagion would be an interesting scientific hypothesis, but doubtful).

From today's Minnesota Public Radio: I-35W bridge collapse could produce U of M traffic headaches ... I am interviewed and the blog gets a mention.

One of the interesting scientific questions that emerges from the tragedy of the I-35W Bridge Collapse is how traffic responds. There are several time horizons for looking at this.

Most immediately are those who are on the link leading up to the bridge. MnDOT's traffic cameras show the cars turning around on the freeway within seconds of the bridge collapsing, before the dust clears literally. "Video footage of the collapse from Mn/DOT traffic camera 628. 6:05 p.m., Aug. 1, shows an edited two-minute clip from a traffic camera at the south end of the bridge. Initially, the camera is pointed to the south away from the bridge. When traffic comes to a stop, the camera pans to the north where the bridge has just collapsed. (wv file)". This is a rational response on the part of drivers who don't know what else may collapse. As my wife says, there are two types of people "those who run towards the meteorite and those who run from it". Survivors are those who ran from it.

Over the next few minutes and hours, word of the bridge collapse spread. My student Shanjiang Zhu has organized MnDOT's loop detector data into a movie that shows the 15 minute traffic counts on all the loop detectors in the Twin Cities, comparing that number with the previous Wednesday's count at the same time of day. Blue indicates lower volumes, red higher volumes. Clearly after the collapse, people heard quickly through various sources (cell phone, variable message signs, radio, etc.), and avoided large swaths of I-35W in the vicinity (which turns blue) and complementary feeder links, while competititve substitute links (Mn 100, I 35E, parts of I-94) saw an increase. We still have to compute how overall traffic volume and Vehicle Kilometers Traveled changed.

Once people were informed, on subsequent days people searched for alternatives. The alternative the first day for some was to avoid driving, but that quickly changed, and different routes became natural substitutes. A second movie compares the counts on the 15 days after the collapse with the average of the previous 8 weeks same day of week (so a Thursday is compared with the eight pre-collapse Thursdays). This illustrates the changes network wide. The
movie is available.

Finally, there may be some longer term adaptations, but we don't have enough information only one month into the changed situation to know about this yet. With colleagues Henry Liu and Kathleen Harder, we have obtained a National Science Foundation Small Grant for Exploratory Research to look at all of these issues in some more depth.

Prior to leaving for London we sold our second car to cash up for the trip. On return, we had two children, two drivers and one car. As I usually walk to work, this is normally fine, but on occassion one has offsite meetings. For this Zipcar and other car sharing programs offer an alternative. Having read the literature on this, and being skeptical, I still signed up to test it.

Zipcar has several locations on campus at the University of Minnesota where they keep cars. For a fixed fee, I get the opportunity to rent cars from Zipcar with a minimum of paperwork and contracts. I can reserve the car online (assuming it is available, which may turn into a problem if demand is high) and then can rent the car for $8 per hour plus tax. This sounds expensive, and requires planning, but in exchange I avoid all the fixed costs of auto ownership.

I am issued a Zipcard, which I swipe over the keyhole on the car I reserved, and electromagically, the car door unlocks. The key is in the car. I am responsible for fueling, parking etc., but presumably Zipcar takes care of maintenance and insurance.

Using the car yesterday went quite smoothly once I figured out the operation of the Zipcard in unlocking the door (it sounds obvious, but isn't quite, and didn't work immediately, though did a second time), and getting out of the garage (which requires the use of the parking garage contract card, which is in the car, but is again not obvious if you have not done so before.

Otherwise, the car was where it was supposed to be, ran fine, and I have had no problems with the experience.

The only problem I foresee is if demand outstrips supply, renting on-demand may become difficult. Zipcar could add vehicles to the fleet, but there may be some lag on this. However, like many network industries, the more members, the more valuable, as it will then be available in more places, and my likelihood of getting a car when and where I want will be easier.

If you are interested in a post-doc or RA position with the Nexus Group, we have several Open Research Positions.

In today's WaPo: China Bans Reporting on Bridge Collapse - washingtonpost.com

"Communist authorities have banned most state media from reporting on the deadly collapse of a bridge in southern China, with local officials punching and chasing reporters from the scene, reporters said Friday."

Apparently physics works in both communist and non-communist countries; but a free press only in non-communist ones.

Article from today's Strib: 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."

The 80:20 rule is a heuristic that people use to suggest that 80% of the benefit comes from 20% of the effort (the values of the parameters may change, but the idea is that a relatively small share of effort gets a majority of the benefit). In one sense this is the idea of diminishing marginal returns, as the last 20% of the benefit requires 80% of the effort. This idea is related to the Pareto principle.

If this is true, the question arises: is the 80:20 rule recursive? Of the first 80% of benefit, does 80% of that only require 20% of the first 20% of effort? In other words, is there a 64:4 rule. Or worse, is there a 51.2: 0.8 rule. If so, then less than 1% of effort gets more than half the benefit.

That sounds like a really good deal to me.

From LA Times: Angkor was a city ahead of its time .. the city had of about a million people spread over an area similar to LA before the industrial revolution.

From BBC: Chinese bridge collapse kills 22

The I-35 W Bridge over the Mississippi River in Minneapolis collapsed at 6:05 pm CDT last night. The Strib reports: 9 dead, 60 injured, 20 missing after dozens of vehicles plummet into river

This is of course a tragedy for those directly involved. I myself was driving under the bridge earlier yesterday with family. Fortunately that was 3 hours earlier, and everyone in my immediate family is safe. It is of course shocking to think about this bridge that I have traveled hundreds of times (about 2 miles from my house) collapsing. Having just returned to Minneapolis about 36 hours ago (I was actually going to say something nice about Northwest Airlines), this was not the welcome I was seeking.

I have some random thoughts below,

== Network Effects ==
What will be the effects of the collapse on traffic?

Networks are complex things. MnDOT has suggested using the roughly parallel MN-280 as a bypass, and have (temporarily?) converted the road to a freeway by turning to green the only traffic light on the road (why was the light never replaced earlier?)

There are other possible substitutes, that MnDOT and the local neighborhoods will not want to encourage as bypasses. For long distance trips, the I-494/I-694 beltway, US-169, Mn 100, and I-35E will one suspect get additional traffic. (hypothesis #1).

For shorter distance trips, traffic that would have gone down I-35W may divert to Mn-280, Broadway to I-94, or Snelling Avenue (which is a limited access highway for a good stretch, and should be immediately have its traffic signals retimed to accommodate additional traffic)

It might take some time for a new equilibrium pattern of traffic to re-emerge. It is still summer vacation period, so the University of Minnesota has not started a full fall semester, and traffic levels are relatively low, giving some change to adjust. The day after Labor Day will be another time to test.

As a result of this however, some other problem sections of road may no longer be as problematic. The merge from I-35W sb to I-94 wb should not cause problems for instance (hypothesis).

There might be interactions with the Crosstown reconstruction, as that is also discouraging traffic from using I-35W a few miles south. It might make more sense now to consider just closing all of I-35 W so they can do the reconstruction faster (assuming closure would make it easier to do the construction under the current design).

== Reconstruction ==

Some recent bridge collapses (I-580 in the Bay Area) were remedied quite quickly. I think this will be longer. First it is a much larger bridge. Second, it will clearly require redesign, as the first design failed for "unknown" reasons (as opposed to a a truck exploding, which may not be worth defending against).

== Structures ==

I am not a structural engineer. This report by my late colleague Bob Dexter is interesting
http://www.cts.umn.edu/Publications/ResearchReports/reportdetail.html?id=617

Fatigue Evaluation of the Deck Truss of Bridge 9340

Robert Dexter, Heather O'Connell, Paul Bergson
March 2001
Report no. Mn/DOT 2001-10

Of course the abstract, while noting problems with the design,it said "As a result, Mn/DOT does not need to prematurely replace this bridge because of fatigue cracking, avoiding the high costs associated with such a large project." This was published 6 years ago , probably finished 7 years ago, and things change. Reports in the news media say the bridge was structurally deficient. We still don't know what element of the bridge failed first, or if the construction on the bridge had any role (one suspects it does, but that is still speculation).

== Politics ==

(1) Allocation of resources to new facilities rather than repair and maintenance.

This is a classic problem in transportation funding. Ribbon cuttings on new projects are much more politically "sexy" 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, 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.

(2) Vetoing the gas tax
Minnesota Governor Tim Pawlenty recently vetoed a legislature-passed increase in the gas tax that could have raised money to repair bridges like this one. The latest 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.

(3) Pointing fingers
It is too soon to say "J'accuse". Most people will probably want to wait for rescue and recover operations to be complete, and then for memorial services, and then for a more thorough investigation. However, MSNBC was starting early speculating in which direction the fingers would wind up pointing.

(4) Funding the stadiums

Minnesota is in the process of building 3 new stadiums (Twins, Gophers, and eventually the Vikings). Is this the best use of local funds? Hopefully this will be a shock to the system.

== U of Mn ==

Keeping with the University of Minnesota tradition, classes will go on today as scheduled. Classes were cancelled on 9.11, but that happened the same day.

== Crisis vs. Opportunity ==

Rebuilding the bridge is of course a crisis, but it is also an opportunity to do something interesting. I speak in particular of air rights. A bridge over the Mississippi is expensive. But imagine having a 2 or 3 story office building hanging from below, or built above the highway. A view of the river from offices is probably among the best in Minnesota. It will not impair other's view of the river especially much, and would generate a significant amount of revenue to pay for reconstruction.

An 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.