San Bruno Blast: New light on welding flaws from the NTSB

Thanks to the NTSB's latest information about the San Bruno gas explosion, the Metallurgical Group Chairman Factual Report, now we know where the crack started. It was in a lengthwise seam (called a "longitudinal weld") rather than where the pipe segments were joined up, end to end (called a "girth weld"). And it started in a particular short segment of pipe (called a "pup").
As a reminder, here's a diagram from page 17 on how the various pups and two long sections joined up. 

Attention is focused on the fragment that extends from Pup 4 on the north, to a fracture in the long joint on the south. (It's marked by a bracket on the left side of the diagram.) 

Originally entrenched three feet below grade, this 27' 8" fragment split open and flew out of the ground, landing in the street a hundred feet away. Here's a photograph of the fragment, from page 19. 

Metallurgists have concluded from close study of chevron marks and fracture faces that the failure started in the wall of Pup 1. It's pictured on page 51:

In this December post I guessed that Board experts had found the initiation site in either Pup 1 or 2, so I was only half-right. 

The crack started not in a girth weld where it connected to another pup or a long section, but a longitudinal seam. This is surprising. At the time when the pipe used at San Bruno was fabricated (late 1940s) such longitudinal seams were normally made in a factory setting. Hydraulic rams and rollers bent a thick steel sheet into a tube shape, then automatic welders joined the edges.

I would have thought that failure was more likely to begin in a girth weld, since girth welds are made in the field and tend to have more quality problems than longitudinal seam welds done in a factory setting. 

To see what factory seams should look like, take a look at the weld shown on page 62. It was in a long section of pipe, not a pup.

The upper surface is the outside of the pipe. Notice that the full thickness of the pipe wall has been joined, with no gaps, cracks, or flaws visible. The only problem visible is a slight misalignment of the two sides when joined, about five degrees off kilter.

For a poorly executed longitudinal seam, see this photo on page 63:

Not coincidentally, this is a cross section from a seam in pup 1, and it's near where the crack first started. 

The welding was done from the outside only, and penetrated to just 55 percent of the depth. According to standards of the day an acceptable weld should have joined 90 percent of the depth. Anyone checking the inside of the pipe later would have seen that the seam hadn't been welded from inside. Instead he would have seen a gap, like the one on the inside of Pup 3 (page 26):

That's not all. Go back to the picture from page 63, and look at the outer surface of the pipe, along the top ... Notice how the pipe wall is rather flat, rather than gently rounded like it should be. 

Apparently somebody took a grinder to the outer surface of the pipe, making the steel wall about .05 inches thinner than when it came out of the mill. The thinning is most noticeable on the right side (the side labeled "counterclockwise").

Why would anybody grind so much steel off the surface of the pipe wall? It would take a fair amount of effort. One hint: the report points out a serious misalignment of the two edges, labeled "radial offset."

It's only one of many quality problems called out. See page 40 for a photo of a section of welding rod found embedded in a girth weld joining Pups 1 and 2:

I expect the Board's final report will dig into how such a sustained system fracture from pipe fabrication through installation could have happened, and gone undetected.

Stuxnet, Iran & SCADA: Compiling the unanticipated consequences

Amid the high-fiving and knuckle-bumping over Stuxnet and the havoc it wrought on the Iranian uranium-enrichment effort at Natanz, a few commentators have brought forward worries about two possible unintended consequences. I'll add a third.

First, a recap of what Stuxnet apparently did. After somebody inserted it into the Siemens-provided SCADA (supervisory control and data acquisition) system used at Natanz, Stuxnet caused some centrifuges to go beyond their red-line limits and break up. 

Not all the Iranian centrifuges were destroyed but it was a big setback. Because operators in the control room normally would have learned from their instruments that this situation was developing early enough to head off the damage, Stuxnet also used a man-in-the-middle attack. Meaning: while things were coming apart, fake data sent to the control room said everything was fine.

One concern already expressed is that the “wrapper” around Stuxnet was rather carelessly put together as far as concealing its creators (news reports suggest the US led off the effort, followed by Israel), and thus could invite a new front in a cyber war. China is no doubt miffed because its factories were affected also.

A second concern is that the West will get complacent about watching the Iranian program. According to the Tehran Times, Iran will forge ahead with enrichment, stux-bugs or no.

My concern: assuming that Iran now harbors serious doubts about its centrifuges, it might resume the work it suspended a few years ago on laser isotope enrichment, or LIS. Unfortunately, it could be a game-changer.

The first revelation of Iran's interest came in August 2002, when the dissident group National Council of Resistance of Iran announced at a Washington, D.C., press conference that Iran had built a laser enrichment facility at Lashkar Ab'ad. After being discovered, Iran allegedly dismantled its LIS gear in 2003.

Why does it matter? If rogue states master the technology, LIS radically increases the risk of nuclear proliferation. To summarize the main points:

• As is well known, it's a lot easier to build a uranium bomb than a plutonium one ... but only after the fissionable material is in hand;
• Fortunately for our peace of mind, it's been very difficult to enrich uranium to sufficient levels for bomb use. This has served as a firewall to proliferation;
• But LIS holds the promise of enriching uranium with small-scale, concealable facilities. Therefore IAEA inspectors will find it very hard to find LIS-equipped enrichment facilities, and if they find them, to know for sure what the facilities are producing;
• So if LIS gets into general circulation, the last significant barrier to nuclear weapon proliferation among rogue states will fall.

The long, slow rise of LIS has been something the press has mostly ignored, concentrating instead on rogue states' banks of gas centrifuges. Maybe it's because gas centrifuge hardware for uranium enrichment has long been established, and is easily visualized and understood. Gas centrifuges for uranium hexafluoride gas are so specialized that inspectors can spot them right away, once they get inside the facility.

LIS by contrast will be very hard to detect. Fortunately, so far, it is only in early emergence stage when it comes to producing highly-enriched uranium that's suitable for nuclear weapons (generally, this is understood to mean the ratio of U-235 isotope is 80% or more, though the percentage could be significantly less). LIS is already feasible enough for GE Hitachi to propose commercializing it to feed a new wave of power reactors. China is building more than 20 nuclear reactors now.

American research opened this Pandora's box. In 1985 Lawrence Livermore National Laboratory developed the laser separation technique, and announced it to the world as a cost-cutting breakthrough in production of reactor fuel that would enable us to cut our prices for fuel being sold to American and foreign power reactors, far below what had been possible with gas centrifuges, a concept dating to the Manhattan Project.

At the time the U.S. was losing business to centrifuge plants in Europe that were undercutting its aging, energy-wasting gas-diffusion plants in Kentucky, Tennessee, and Ohio. Said an assistant secretary at the Department of Energy: ''This is the way of the next century. It's the world's best way of enriching uranium.''

There are three common methods of laser separation now, but the most developed (and the one Iran has taken an interest in) is called atomic vapor laser isotope separation, or AVLIS. This was the approach developed by Lawrence Livermore.

Here's how AVLIS works. First electron beams produce uranium gas from a slab of unenriched metal. Then a two-stage laser goes to work. The first stage is a high-power copper-vapor laser, which sends blue light over to a dye laser. The dye laser sends red-orange light of an extremely precise wavelength into a cloud of uranium atoms. If tuned with great precision the laser will knock outer-shell electrons off U-235 atoms but not U-238 atoms, because their masses are slightly different. The laser causes the U-235 atoms to become positive ions and fling themselves against a negatively-charged metal plate for removal later. It’s necessary to send the enriched vapor through six stages to bring it to weapons purity.

If this sounds impossibly high-tech for a rogue nation or group, it’s not. 

 

Worldwide, hundreds of university and government labs already use laser-separation equipment. Usually it’s for peaceful research purposes, but not always. Several labs, including one at Taejeon, South Korea, already have used laser separation to make a few hundred milligrams of weapons-grade uranium.

The IAEA shut down the Republic of Korea’s effort in 2004 after discovering that wisp of enriched fuel but in most cases it’s going to be very difficult to know whether a given set of AVLIS equipment is part of a concealed weapons program or something legitimate. That’s because certain high-tech industries, such as electronics, need certain metals of great isotopic purity, just like nuclear weapons manufacture does, and laser isotope separation is an accepted way to obtain it. So confirming the existence of weapons-purposed AVLIS equipment will be greatly more difficult than spotting high-speed centrifuges for corrosive uranium hexafluoride gas, which are unique and immediately recognized by weapons inspectors.

While it would take dozens of AVLIS machines to make enough material for one bomb a year, the machines are compact enough so that all of them would fit inside the floor space equal to a big-box discount store, and therefore would not be difficult to conceal in tunnels underground. 

If and when AVLIS machines are set up for making weapon-grade uranium, they're most likely to go into tunnels under existing military bases. It's common for military bases to have underground storage.

The pace of LIS is likely to accelerate with advances in industrial lasers, which each year have been dropping in price while going up in efficiency and precision. According to some experts, the eventual spread of AVLIS is as obvious as the spread of advanced chip-manufacturing techniques for computers, which showed up in many nations after a few companies worked out the essential details. 

This suggests to me that anti-nuke-smuggling measures, and (for the worst-case scenarios) forensic analysis, are still timely.

Clouds, yearning to be 3D

Clouds come in layers! 

While writing a story for Smithsonian in 1997 I interviewed a tower hand who recalled climbing into a grim, gray old overcast to do some broadcast-tower maintenance work. But after a few minutes in the murk, he emerged to see a brilliant blue sky above. He stopped to stare at the cloudscape, mist still clinging to his boots. No other people were in view. It was a world made new.

Interesting visual effects emerge when a high cloud casts a shadow on a low cloud. From the ground, sometimes these shadows appear as fuzzy silhouettes. The one on the right looks like a stylized thunderbird.

The following illustrates how altostratus can be extremely thin and well defined, like a sheet of tinted glass. I took this over Wisconsin from an airliner at 32,000 feet. It was overshadowing stratocumulus undulatus below.

In the next photo, it's a case of undershadowing: a low cloud (a jet contrail in this case) throwing its profile on a higher one at sunset. I took this in Minnesota last November. 

Note the rough similarity to the infamous California contrail. It's coincidental!

List o' Publications

Answering this question: 

"What else have you written besides Inviting Disaster and The God Machine?"

I started in 1980 with an article about the Pantex nuclear-weapons plant in Amarillo, Texas, and have been writing pretty regularly since, with seventy features or columns published.

Here's the article list, from most recent to most ancient.

"Grand Central Terminal," Invention & Technology (in process)

"The Steam Shovel – Inventor, Richard P. Thew," Invention & Technology, Fall 2010

"Build-It-Yourself Helicopters," Air&Space/Smithsonian, August 2010

"Remotely Operated Vehicles Come of Age," Invention & Technology, Summer 2010

"The Shovel That Helped Build America," Invention & Technology, Spring 2010

"The Other Renewable Energy," Invention & Technology, Winter 2009

"Spanning the Ages," Invention & Technology, Fall 2009

"Hot Rod Helicopters," Air&Space/Smithsonian, Sepember 2009

"Heavy Rescue," Invention & Technology, Summer 2009

"From Bazookas to RPGs," Invention & Technology, Spring 2009

"One More Second," Air&Space/Smithsonian, December 2008

"The Third Age of Industry," Invention & Technology, Summer 2008

"Air America’s Hush-Hush Helicopter," Air&Space/Smithsonian, March 2008

"I Dream of Choppers," The Boston Globe, November 18, 2007

"Ring of Fire," Air&Space/Smithsonian, June-July 2005

"A Catch in Time," Mechanical Engineering, March 2004

"When CO₂ Strikes," Popular Science, August 2003

"A Tragic Mix of Oil and Water," Popular Science, January 2004

"Here is the church, here is the -- Watch out! " Popular Science, June 2003

"U.S. Flirts with Runway Disaster," Aviation Week & Space Technology, November 5, 2001

"Helluva Catch," Air&Space/Smithsonian, August-September 2004

"Stand By Me," Engineering Times, November 2001

"Getting in Deep," Smithsonian, November 2001

"High Tension," Air&Space/Smithsonian, August-September 2004

"Second Wind," Smithsonian, March 2000

"The Spirit of Knob Noster," Air&Space/Smithsonian, Oct-Nov 1999

"Good Days at Black Rock," Smithsonian, April 1999

"Casting a High-Tech Net For Space Trash," Smithsonian, January 1999

"Back on the Line," Air&Space/Smithsonian, October-November 1998

"Hallelujah, I'm a Bum," Smithsonian, July 1998

"We got us some sky today, boy!" Smithsonian, July 1997

"Bang! went the doors of every bank in America," Smithsonian, April 1997

"Out From the Shadow," Air&Space/Smithsonian, May 1996

"How the great war on war surplus got won - or lost," Smithsonian, December 1995

"Congress couldn't have been this bad, or could it?" Smithsonian, November 1995

"Remember, Jimmy, stay away from the bottom of the shaft," Smithsonian, July 1994

"Now that everything's portable, getting around can really be a drag," Smithsonian, January 1994

"It's not easy going eye to eye with today's newfangled fires," Smithsonian, May 1993

"Call me Great or Wise, just don't call me Disorganized," Smithsonian, February 1993

"Goodbye telephone," Smithsonian, February 1992

"There are new signs of energy out in the Kansas oil patch," Smithsonian, March 1991

"Bachelor Living and the Art of Messismo," Smithsonian, Feb. 1991

"County seats were a burning issue in the Wild West," Smithsonian, March 1990

"At science fairs, there's not much playing around," Smithsonian, September 1990

"At air traffic control school, it helps to memorize in your sleep," Smithsonian, January 1990

"Tomorrow's Energy Today," Audubon, January 1990

"Flying cars were a dream that never got off the ground," Smithsonian, February 1989

"How we got ready for a war that was never fought," Smithsonian, December 1988

"Flying on a wing and a prayer, Voyager heads for a last rendezvous," Smithsonian, September 1988

"The Ships that Broke Hitler's Blockade," American Heritage of Invention and Technology, Winter 1988

"The Cable Under the Sea," American Heritage of Invention and Technology, Fall 1987

"Spindletop," American Heritage of Invention and Technology, Summer 1987

"Breaking codes was this couple's lifetime career," Smithsonian, June 1987

"Titanium: for when you care enough to use the very best," Smithsonian, May 1987

"The Road to Radar," American Heritage of Invention and Technology, Spring 1987

"NASA's giant research balloons are out of sight," Smithsonian, January 1987

"Standing up to Earthquakes," American Heritage of Invention and Technology, Fall 1986

"Anything can be counterfeited, and these days, almost everything is," Smithsonian, July 1986

"When pilots' worst nightmares come true, in simulators," Smithsonian, June 1986

"One Glorious Ham," Harvard Magazine, November-December 1985

"Learning from the Big Blackouts," American Heritage of Invention and Technology, Fall 1985

"The Great American Junkyard: going from wrecks to riches," Smithsonian, March 1985

"Age-old battle to keep safes safe from 'creepers, soup men and yeggs,'" Smithsonian, July 1984

"Learning to Live with Plutonium," Science Digest, July 1984

"Engineers vs. the eons, or How long will our monuments last?" Smithsonian, March 1984

"Movers and Shakers," Texas Monthly, April 1981

"Who Owns Texas?" Texas Monthly, June 1980

"Ten, Nine, Eight, Seven . . .," Texas Monthly, January 1980

Tom Swift Meets Google Translate: Mr. Sharp is about to explode

There's a small slew of articles out this week about Google's new app, allowing real-time translation over the Android 2.1-and-higher phones. Amazing! Useful! According to this piece on FoxNews, Nothing's Lost in Translation. 

Well, we'll see about that. Here's an article comparing different machine translators and how they hold up in use. 


This interesting Op-Ed piece by David Bellos explains how Google has been building up its Translate program over the years. In a word, Google has piled up a world-beating archive of translated materials (UN proceedings, famous books translated into multiple languages, and much more) in which humans of yesterday did the work for computers of today. 

Google had to come up with an algorithm so its computers can choose among the many stored possibilities, given that stock phrases like "I'll believe that when I see it" have undergone a lot of translations over the years. 

Meanwhile, Google has been sharpening up its voice-recognition skills. You may have read in articles like this one that the main reason Google offered a free voice-activated directory-assistance service beginning in 2007 was to accumulate a dataset about the multifarious ways in which people pronounce the same words different ways. GOOG-411 is shut down now, but the data lives on.

Google's web-based text translator has been available for several years, for free. Not needing to do any voice intepretation, it should be more reliable than a voice decoder. I decided any good text translator should be able to move smoothly through more than one language, so I took a hunk of Tom Swift and His Airship and ran it into Persian, then ported the output over to Turkish, and back to English.

First, the breakneck storyline: There is an explosion of a gas cylinder, and a run-in with the local thugs! Then Tom and his buddies head off to adventure in the Red Cloud, his 80-mph dirigible!! Later they have to rush back to Shopton to clear his name!!! Because he's been framed with a bank robbery!!!!

I've found after various experiments on this and other old texts that when forced to plod through two languages, Google Translate is enough to give the general idea of what's happening, but adds many unique twists to characters, storyline, and settings. Occasionally it introduces modern notions like rocket-propelled grenades into juvenile literature of the early 1900s because the translated phrase it is borrowing from includes them. It also creates new relationships. Here's the original: 

"Well, turn on the gas, Mr. Sharp," advised Tom Swift. "I'll watch the pressure gauge, and, if it goes too high, I'll warn you, and you can shut it off."

Double-translated through Persian and Turkish: 

"Well, turn on gas, Mr. Sharp," advised Tom Swift. "My barometer, clock and I is too high, I love you, if any, and to warn him off."

A few paragraphs later, disaster is looming. Original:

"Shut it off!" cried Tom quickly. "It's coming too fast! Shut her off!"

The man sprang to obey the command, and, with nervous fingers, sought to fit the wrench over the nipple of the controlling valve. Then his face seemed to turn white with fear.

"I can't move it!" Mr. Sharp yelled "It's jammed! I can't shut off the gas! Run! Look out! She'll explode!"

 Translated:

"That Stifle!" Cried Tom quickly. "This is a very quick! Strangle him!"

Man to obey commands, jumped and nervous fingers, looks good key control valve through the breast. Then his face seemed to turn white with fear.

"I can not move!" Mr Sharp shouted: "This is my story! Run! See gas has not been cut! I want to explode!"

So they carry out a lessons-learned investigation. Original:

One trial showed him that the valve there had jammed

Double-translated, there are legal implications: 

Courts have too much on this subject, to educate children with milk

Okay, it wasn't fair of me to ask a free translator to grind a text through two languages and bring it back to English. But it does make me a bit cautious about using it for negotiating treaties or  business deals.

Uncharted Waters, 1972: Nuclear sub Pogy finds a new mountain

The July 1972 issue of Popular Mechanics featured an article about the work of the research ship John N. Cobb. As the ship detoured to investigate a flock of seabirds feeding in a spot 270 miles west of Seattle, the sonar man was astonished to find the seafloor profile rising fast. Astonished, because this was an area where the sea was thought to be a good two miles deep.  

Cobb had found an uncharted seamount that rose to within 110 feet of the surface. That isn't very deep for the open waters of the North Pacific. The largest oil supertanker ever built, Seawise Giant, drew 81 feet of water when fully laden.

Coincidentally, the crew of US Navy attack submarine Pogy (SSN-647) was soon to discover another uncharted mountain while on patrol elsewhere in the Pacific. 

Pogy was a Sturgeon-class nuclear-powered attack submarine, equipped with nuclear-tipped SUBROC missiles. In 1984 it achieved a degree of fame when mentioned in Tom Clancy's The Hunt for Red October. In the novel, Pogy was one of two submarines escorting October back to the US.

I don't have all the details, but have heard that Pogy was running at top speed when the incident happened (Fall 1972), or about 30 knots. It struck the mountain once, perhaps followed by a second, glancing blow. It was violent enough to throw sailors to the deck and to cause considerable damage to the bow section. 

In some respects Pogy's crash was more severe than the fictional one depicted in The Abyss; but in this case, submarine and crew survived. The crew was able to reach the surface by using the emergency-blow system installed in submarines built after the April 1963 loss of Thresher. Pogy went to dry dock for repairs, perhaps at Point Loma, CA. 

The PM article describing Cobb's discovery can be found on Google Books, here. As far as I know, Pogy's close-call incident has not appeared in the public literature, other than as a few brief references by crewmen (years later) to an impact with undersea terrain.

State of the Art Health Care, 1944

Following up on my previous post about the industrial boom of World War II on the home front. The severe shortage of workers led to interesting innovations by some employers; one was managed health care.

Americans of the 1940s complained about the costs of medical care, but spent comparatively little of their income on it. (We now spend twelve times more on medical care in constant dollars than we did during the war.) With the exception of wealthy people who frequented topflight private hospitals such as the Mayo Clinic, most Americans made do with local doctors’ offices, with only rare visits to hospitals because of the fees. 

Doctors’ offices (which served several thousand people each) had no access to medical diagnostics. There was no penicillin available to any civilian doctors until the end of the war, so blood poisoning was usually deadly. Many towns and small cities had no ambulance service. They relied on police cars and even hearses to get people to the hospital. 

The emphasis was on treating acute needs only: broken arms, childbirth, and care of accidents. There was no medical intervention to save people near the end of what was seen as the natural life span. Americans didn’t like the medical system much back then either, but one exception was Henry J. Kaiser’s prepaid health care plan.

Why did Kaiser go to the trouble of setting up a parallel medical system, when he was supposed to be focused on building ships? All defense industries suffered greatly from turnover. They spent money to train workers on how to wield expensive tools, then lost them to competitors … except at Kaiser operations. One reason was his health care plan. It was called Permanente, after a creek near one of Kaiser's cement plants. His wife Bess liked the name.

Wartime wage caps prohibited employers from raising wages, but that law didn’t prohibit employers from providing benefits that workers paid for and that they valued. Kaiser had started providing prepaid health care while building Grand Coulee Dam. At the Grand Coulee job, a fee of 50 cents per worker per week had covered the expenses. The economics worked. In three years he paid off all the buildings and all medical equipment (including a new air-conditioned hospital, which even the private hospitals didn’t have).

He continued the practice in subsequent years, discovering that if every worker paid into the system, healthy or not (a critical requirement to make it all work, and one that the unions helped enforce), Kaiser could pay for clinics and hospitals to care for 120,000 shipworkers, and later their families too. 

The Kaiser organization continues today, as the managed health care plan Kaiser Permanente.

High Taxes, Low Unemployment: A lesson from WW2

Rather amusing to hear generalizations from politicians about how taxes must inevitably go against job creation. Here's a quote from Roy Blunt of Missouri, now a senator:

As I spoke with families and employers all over Missouri this last year, I heard one thing repeatedly: Job-killing taxes and uncertainty are the biggest deterrents to job creation.

Law of nature? As incompatible as matter and anti-matter? Apparently not.The lowest unemployment rate in American history, 1%, came at a time of very high taxes: that was the industrial boom of home-front America during World War II. As a writer for The Saturday Evening Post put it in 1943, “An orangutan with winning ways could get a job.” 

During the war, income-tax rates on top earners hit 90%. 

'Tis true that many downsides went along with the industrial boom that pulled us out of the Depression: high rates of workplace accidents, profligate use of resources, and gross pollution. (When writing about the de-mobilization of surplus after the war, I came across accounts of a munitions factory where the soil was so contaminated it was explosive to a depth of three feet. A place where even angels might fear to tread.)

Outside of meeting an all-out crisis, such a command-and-control economy can't be sustained, nor should it be.

But if a crisis comes that requires total mobilization of human and industrial resources, it's worth remembering that productivity, low unemployment, and high taxes can get along well.

AASHO Road Test: The gold standard of testing

Driving Son No. 2's drum set back from Chicago, taking I-90/I-39 near Rockford, IL, reminded me of an engineering history landmark, not far south.


It's just off I-80 near Ottawa, Illinois: the remnants of a two-year pavement and bridge test undertaken prior to construction of the interstate highway system. It was sponsored by the feds and the American Association of State Highway Officials, (now AASHTO). Trucks operated by Army recruits drove around five loops from late 1958 into 1960.

The loops tested a wide variety of pavements and bridges. A sixth loop was left untraveled, as a control; the other five saw progressively higher weights of vehicles. Operations went on night and day, employing as many as 126 trucks. Some bridges failed after heavy use; some bridge designs held up so well that the organizers had to run super-heavy loads across the spans to hasten their destruction, since time was running out. In the 14 lane miles available there were more than 800 combinations of pavement and sub-bases. Here's a 50th anniversary article that appeared in Engineering News Record.


One outcome of the million-cycle study was to disprove a theory from the industry that a layer of gravel laid under rigid pavement could prevent the "pumping" of support material from under the pavement. The AASHO test led to pavement designs that held up much better. 

The Road Test shed light on the extent of damage caused by heavy truck axles, compared to cars. When a pothole in a highway causes havoc today, impacts from heavy trucks are usually a contributing cause.


But no test is accurate forever. Today's truck trailers have air suspensions, which cause less damage than old-style leaf springs for an equivalent axle load. New tests should include the effect of specialized hauling vehicles like concrete trucks, that can weigh as much as semis but pack that weight into a much shorter wheelbase, which can make a big difference on bridges. 

Tests should take into effect weigh-in-motion data that some states collect, which reveal how much weight trucks actually are carrying compared to what the law says they should carry. the first years of Montana's WIM scale data showed that nine percent of trucks on the major routes checked were overweight by an average of three tons before enforcement began.

One of the more obscure lessons from the Road Test is that as the speed of trucks rise, the stress they impose on bridge structures can go up dramatically if the deck surface is rough. Hence my comment on the I-94 bridge collapse in this post: roughness in the bridge-deck pavement caused by milling (namely, two-inch height differences) could have added stress that played a part in the collapse. Traffic speeds should have been held down.


Whether on a big scale or a smaller one, rigorous and realistic highway infrastructure tests are important because we need more information than computer models will tell us. We need experiments to know how well roads and bridges are going to hold up against the stresses of a new, leaner economy ... the Third Age of Industry.