Canada’s Crumbling Infrastructure

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).

“I-35W bridge collapse could produce U of M traffic headaches”

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.

I-35W bridge collapse – What happened on August 1st and after

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.

Nexus Group Open Research Positions

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

China Bans Reporting on Bridge Collapse

In today’s WaPo: China Bans Reporting on Bridge Collapse –
“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.

I 35W Bridge repair

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.”

Is the 80:20 rule recursive?

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.

Antecedents of Urban Sprawl

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.