The American public has been learning a lot about bridges this week. The catastrophic collapse of the I-35W bridge that crossed the Mississippi to Minneapolis brought home to the man in the street just how bad the condition our national infrastructure is in. Since then, the editors and correspondents of the nation's daily papers and nightly news broadcasts have been asking the questions 'why did it happen?' and 'could it happen in our town?'
The bridge that fell down was a steel 'Arch Deck Truss Bridge' spanning 1,907 feet. A key feature of the design was a single 485 arch, erected 64 feet above the river. It was used to avoid putting piers in the river, which might interfere with traffic on Old Man River. The bridge was 108 feet wide, with room enough for 8 lanes, providing a crossing for 140,000 vehicles daily. It was opened in 1967 and, apparently, regularly inspected (1). As a regular visitor to Minnesota myself, I've driven over the bridge several times and, like most of my fellow drivers there, taken it completely for granted.
The dramatic event of August 1, 2007 has sent the federal and state administrations into overdrive, commissioning emergency inspections of the condition of other bridges nationwide,
"Especially those similar to the steel-deck truss span that collapsed in Minneapolis. There are about 700 such bridges in the USA. New Jersey Gov. Jon Corzine went further, promising evaluations of all 6,400 local, state and federal bridges in his state, regardless of owner" (2).
While it appeared it was a unique tragedy, those with longer memories knew otherwise. As USAToday reported:
"In 1983, a 100-foot span of the Mianus River Bridge, part of Interstate 95 in Connecticut, came crashing down without warning in the middle of the night. At least four four deadly bridge collapses on major thoroughfares have occurred since then - on the New York State Thruway, in Tennessee, in California and now in Minneapolis" (3).
So what went wrong in Minnesota? At this point, no-one knows with any certainty, though theories abound. Evening TV newscast hosts have interviewed experts who gave their best guesses (4). Experts? What about those experts? One of my colleagues reminded me recently of the definition of an expert - "'X' is an unknown quantity, and a 'spurt' is a drip under pressure". I've also heard the definition "any man from out of town with a PowerPoint presentation".
The credibility of the experts whose opinions have been acted upon have already been called into question. As the BBC reported
"The governor of Minnesota, Tim Pawlenty, said "Experts that we rely on, technical experts and engineers, made some decisions about what needed to be done".
"They thought they were making an appropriate decision for their reasons, and now those decisions will have to be reviewed" (5).
In the defence of these experts, successive surveys of the nation's bridges by them had highlighted a variety of deficiencies. Not just in Minnesota, but every state has interstate highway bridges that government appointed inspectors have deemed structurally deficient. The term 'deficient' means a bridge's deck, main structure or foundation were deemed to be in poor condition or worse owing to deterioration or damage of some kind. (6).
For example, in 2003,
"More than one of every four bridges was designated as "structurally deficient" or "functionally obsolete"." That included nearly 6,500 bridges on the nation's most important highways. Minneapolis' Interstate 35W bridge was put on the list, too" (7).
Some 70,000 bridges are deemed deficient in the USA. According to the The Road Improvement Project, 2005 survey, of the 6,211 bridges in my home state of Texas, just 1% were deemed deficient. (Great job TxDoT!). Compare the Lone Star State to, say, New York state, which has 2,090 bridges and 16% of them were deemed deficient. Or Rhode Island with a mere 123 bridges, but 24% classified as deficient (8). It's a very mixed picture. Clear is that it is a national problem, an expensive one to fix and one we have been putting off for too long.
Hardly have journalists finished commending the citizens of the state for their legendary trait of Minnesota nice, but already the finger pointing has begun. The local Twin Cities' newspaper Pioneer Press reported:
"Lt. Gov. Carol Molnau's other job - as commissioner of the [Minnesota] Department of Transportation - put her squarely in the hot seat during a Friday afternoon news conference. "Our inspectors are known nationally because they're good,'' she said. "Believe me, there was no intent, nor neglect, nor malice, nor do I think any should be implied" (9).
And:
"Minnesota Gov. Tim Pawlenty has been criticized in the past for not hiring a full-time Department of Transportation commissioner, rather than giving the lieutenant governor the job. Democratic-Farmer-Labor lawmakers have often criticized Molnau's management of the Transportation Department.
"Asked whether she was doing both jobs well, she said, "I think I've been doing it well (the job of transportation commissioner). I do spend the bulk of my time with MnDOT. I could spend more time visiting schools and doing things with children, but instead I've taken on the role for the state's infrastructure" (10).
As commentators reflect on the causes of the catastrophe, we have been reminded of the circumstances under which the I-34W bridge and others like it, were built. The 'I' in I-34 stands for Interstate, which informs us that that it was conceived as part of The Interstate Highway System. The idea for this goes back to 1921 but it did not get the go-ahead until
"The interstate system was authorized by the Federal-Aid Highway Act of 1956, popularly known as the National Interstate and Defense Highways Act of 1956. It had been lobbied for by major U.S. automobile manufacturers and championed by President Dwight D. Eisenhower - who was influenced by both his experiences as a young soldier crossing the country in 1919 following the route of the Lincoln Highway and his appreciation of the German autobahn network - as a necessary component of a national defense system. It would be able to provide key ground transport of military supplies and troop deployments.
"Although construction on the Interstate Highway system continues, the removal of the last traffic signal in Interstate 90 in Wallace, Idaho, on September 15, 1991 is often cited as the completion of the Interstate System.
"The initial cost estimate for the system was $25 billion over twelve years; it ended up costing $114 billion and taking 35 years to complete" (11).
The entire system, as of 2004, had a total length of 46,837 miles (75,376 km).
It was a fantastic achievement. It has been estimated that the US completed its interstate system in one-fourteenth the time the Romans took to connect their Empire with roads. OK, not an entirely fair comparison. American engineers did have mechanised diggers, tunnel drilling equipment and high tech surveying tools.
Is there anything the Romans can tell us about road bridges and their upkeep? Actually yes, there is. If there's anything they are famous for, it's roads and bridges. To put the achievement in context,
"At its peak, the Roman road system spanned 52,819 miles (85,004 km) and contained about 372 links" (12).
One estimate is that there were 2,000 bridges in the Roman Empire (13). Some bridges were made entirely of stone or in combination with, concrete, bricks and mortar, while others had stone and concrete footings but wooden superstructures (14).
The longest road bridge the Romans ever built was the one erected over Danube for Emperor Trajan (98-117CE).
"The structure was 1,135 meters in length (the Danube is 800 meters-wide in that area), 15 meters in width, and reached 19 meters in height (measured from the river's surface)" (15).
It was the expression of centuries of accumulated expertise in civil and military engineering using only natural materials and human labour, supplemented by animals:
"Its engineer, Apollodorus of Damascus, used wooden arches set on twenty masonry pillars (made with bricks, mortar and pozzolana cement) that spanned 38-meters each" (16).
The Romans recognised the crucial importance of maintenance of bridges and highway infrastructure. Indeed, Sextus Julius Frontinus, Manager of Aqueducts at Rome, who wrote de Aquibus urbis Romae, the only surviving manual on Rome's water infrastructure, commented on the importance of the upkeep of aqueducts. He described it as his "chief function" (17). That was in 98CE.
In the City of Rome (urbs Romae), so important was the construction, repair and maintenance of bridges that there was a full-time appointed official, the pontifex maximus, 'chief of bridges', who was also an important religious priest (18). Indeed, this religious aspect of the still endures today in the title 'Pontiff', the alternative name for the Pope.
How did they pay for new construction, repair and maintenance? Financing road and bridge building was a Roman government responsibility. During the Imperial Period, it was the army (exercitus) that built the roads that penetrated into newly conquered territories, but when the army moved on and towns were founded, their care passed into civilians hands.
"Maintenance, however, was generally left to the province. The officials tasked with fund raising were the curatores viarum, whence English word 'curator'. They had a number of methods available to them. Private citizens with an interest in the road could contribute to its repair. High officials might distribute largesse to be used for roads. Censors, who were in charge of public morals and public works, were expected to fund repairs sua pecunia (with their own money). Beyond those means, taxes were required" (19).
It would be a mistake to think that any Roman citizen could use the roads and bridges free of charge. Tolls were a common feature of a Roman traveller's life, especially at bridges. Often they were collected at the city gate (20).
The blending of public and private money to fund projects offers a viable solution for the modern day:
"Governments need to tap private investors, says Chris Lawton, a partner in Ernst & Young, a firm that designs such deals. The United Kingdom finances 10% to 15% of its infrastructure needs through private investment, he says. That could mean more toll bridges and roads, or transferring long-term maintenance of a bridge to a private firm, he says" (21)..
The fabulous M4 Severn Bridge that I drive over from England on my visits to Wales is managed and operated by Severn River Crossing PLC, a non-quoted public company. As of January 2007, the toll is £5.10 for a car, increasing to £15.30 for a heavy goods vehicle (22). The older mile-long M48 Bridge, which opened in 1966 and is still operational, is undergoing repairs right now to the tune of £20 million (23). It follows a UK Highways Agency study costing £3 million and completed in 2006. The culprit identified there was corrosion in the suspension cables (24). Note that maintenance on the bridges is active and ongoing.
So to the rebuilding of Minneapolis' I-35W bridge. According to The Pioneer Press
"State transportation officials this afternoon vowed to have a new I-35W bridge up and carrying cars by the end of next year [2008].
"The ambitious goal came in an afternoon news briefing by Minnesota Department of Transportation Assistant Commissioner Bob McFarlin. Aiming to "rebuild the bridge as quickly as possible," McFarlin said the state planned to award a construction contract next month, with the hope "that the bridge could possibly open for service late next year" " (25).
Of course, he's an expert so he should know. But consider general Julius Caesar. He built not one but two bridges over the Rhine in the 50s BCE. With 40,000 pairs of hands at his disposal, the bridge took a mere 10 days to construct using local timber (26). That 10 days likely included cutting down the trees and preparing the timbers. Eighteen days later he ordered it taken down.
"Two years later, close to the site of the first bridge, possibly at today's Umitz (near Neuwied), Caesar erected a second bridge, built "in a few days", as described in Liber VI. His expeditionary forces raided the country side but did not encounter significant opposition as the Suebi retreated. Upon returning to Gaul, the bridge was taken down again" (26).
Because he could.
Then there was that bridge that Apollodorus designed and built for Trajan. It took just two years, between 103-105CE:
"One possible explanation is that the river [Danube] was diverted during the bridge's construction" (27).
(and that without the use of Caterpillar dozers, diggers or skidders (28)).
Diverting the Mississippi may not be needed to build the new bridge in the twenty first century - after all, it's going to be less than 2,000 feet long. But its construction nevertheless poses considerable engineering challenges.
The greater problem is what to do about the 700 other 'Arch Deck Truss Bridges' in the USA, many identified as deficient. In that regard, the Romans do have an important lesson for us (29). That is to make the upkeep of bridges a matter of national importance and fund it accordingly. But don't delay. As Frontinus might have said, "Tempus fugit!"
References
Frontinus, Stratagems and Aqueducts (Sex. Julius Frontinus, de Aquis urbis Romae), Loeb Classical Library, translated by C.E. Bennett (1925)
- http://www.usatoday.com/news/nation/2007-08-02-bridge-cover_N.htm
- http://www.usatoday.com/news/nation/2007-08-02-bridge-cover_N.htm
- http://news.yahoo.com/s/usatoday/20070803/cm_usatoday/abridgeinamericajustshouldntfalldown
- http://www.time.com/time/nation/article/0,8599,1649423,00.html?cnn=yes and http://www.cnn.com/2007/US/08/02/bridge.infrastructure/index.html for examples
- http://news.bbc.co.uk/1/hi/world/americas/6930822.stm
- http://www.usatoday.com/news/nation/2007-08-02-bridge-cover_N.htm
- http://news.yahoo.com/s/usatoday/20070803/cm_usatoday/abridgeinamericajustshouldntfalldown
- http://www.usatoday.com/news/nation/2007-08-02-bridge-cover_N.htm
- http://www.twincities.com/collapse/ci_6541268
- http://www.twincities.com/collapse/ci_6541267
- http://en.wikipedia.org/wiki/Interstate_Highway_System
- http://en.wikipedia.org/wiki/Roman_roads
- Michael Guillen in Where Did It Come From? Ancient Rome:The Mobile Society which aired on History Channel International on August 4, 2007
- http://en.wikipedia.org/wiki/Roman_bridges
- http://en.wikipedia.org/wiki/Trajan's_bridge
- http://en.wikipedia.org/wiki/Trajan's_bridge
- Frontinus, de Aquis urbis Romae, I, 17
- http://en.wikipedia.org/wiki/Pontifex_maximus
- http://en.wikipedia.org/wiki/Roman_roads
- http://en.wikipedia.org/wiki/Roman_roads
- http://www.usatoday.com/news/nation/2007-08-02-bridge-cover_N.htm
- http://en.wikipedia.org/wiki/Severn_bridge
- http://news.bbc.co.uk/1/hi/wales/south_east/6927852.stm
- http://news.bbc.co.uk/1/hi/england/gloucestershire/6425649.stm and http://news.bbc.co.uk/1/hi/magazine/6929777.stm which states that in the UK, there are 17,000 road bridges on its motorways and A-roads, but none are of the Arch Deck Truss design
- http://www.twincities.com/allheadlines/ci_6545466?nclick_check=1
- http://en.wikipedia.org/wiki/Caesar's_Rhine_bridges
- http://en.wikipedia.org/wiki/Trajan's_bridge
- To see what a skidder looks like, see http://www.cat.com/cda/layout?m=37840&x=7
- The so-called Ponte di Tiberio in Rimini, Italy still carries traffic to this day. It was completed in 21CE. For pictures of this 5-arched bridge made of Istria-stone, see http://www.virtualtourist.com/travel/Europe/Italy/Emilia_Romagna/Rimini-144910/Things_To_Do-Rimini-Tiberios_bridge-BR-1.html The oldest still standing Roman bridge is the Pons Aemilius in Rome, completed in 142BCE, see http://en.wikipedia.org/wiki/Pons_Aemilius
