>> up next on a second look, what caused this bridge and this bridge and this bridge to come crashing down? and what does it mean for people who cross bay area bridges everyday? that is straight ahead on a second look. good evening an welcome to a second look. i'm julie haener. tonight, our bridges, are they safe? caltrans has been debating this

on the eastern span of the bay bridge and the i-5 bridge north of seattle sgajit river collapsed. three people inned up in the water but survived. it was the wind and the bridge design that led to the bridge collapse of tacoma. wind eventually brought down the bridge. at the time it collapsed, the tacoma narrows bridge was the thinker longest suspension bridge in the world right after the gorge washington bridge and the golden gate bridge. in 1961, a storm caused the golden gate bridge to cause

similar twisting, enough to cause some minor damage. as a result, engineers retro fitted it by putting braces on it that kept it from twisting dangerously in high winds. in 1967, another suspension bridge collapsed. this one over the ohio river. the silver bridge connected ohio and west virginia. it might be of particular interest because it was a small crack in an aybar that led to the destruction of the bridge and the death of 46 people. >> it is 1928 and suspension bridges are being built all across america. new designs an new materials make for rapid construction. this is the silver bridge

crossing the ohio river at west virginia on it's opening day. after barely 40 years, the design and the materials used came to haunt them. on december 15, 1967, the bridge fell in less than one minute with the loss of 46 lives. a 20-year-old eyewitness was charlene wood. >> i was on the bridge that night when it fell. i was coming home from work. there was a trembling and a noise i couldn't even describe. i thought something had hit the bridge and i decided i wasn't going to cross it so i threw the car in reverse and as i was backing, the car stalled but kept going. as i was able to get it stopped, the bridge fell in front of me and my wheels were on the ledge there. >> but what was the cause?

was it an accident? carelessness? inadequacy in the design? in a suspension bridge, the outermost supporting chains exert a downward force on the towers. the deck is supported from the cabling system using a system of vertical hangers. these hangers are also in tension. the bridge should be designed so that the deckliation of any one section of the structure does not lead to collapse. these days, the bridges use cables spun from many wires. but the chains in the silver bridge was formed out of long lengths of steel. theseeye bars were put together

the same as a chain in a bicycle. a bolt was used to chain them together. the resulting joints can then move in response to the forces placed on them. the problem couldn't just be this bridge was a suspension bridge using eye bars because that was a known technology with many contemporary examples. the city of pittsburgh has three suspension bridges. known collectively as the three sister bridges, all employ eye bars in their suspension chains. they were constructed at the same time as the silver bridge and are still standing. they have a marked difference in their design. this is the sixth street bridge. the eye bars are in clusters. the failure of any one will not cause a collapse of the structure. >> i could see what was

happening an i just stood right here and watched the whole bridge. >> what did it look like? >> it is like my little boy said. you would build a bridge out of a child's building toys and take a stick and just knock the supports out from under it. >> after the bridge collapsed, congress formed the bridge inspection program that included underwater inspection. -- a 200-foot section of that bridge fell 80 feet killing ten people. charles feldman fired this report after the collapse. >> rescuers had to wait before the waters reseeded before pulling bodies from the swollen

creek of the bridge that collapsed. the incident followed two days of heavy rainfall in the season. the region was on the heavy traffic freeway on the northeast corridor. in the foreseeable future, drivers will have to take detours. at least four vehicles are believed to have plunged into the creek as a 400-foot chunk of the span crumbled. the span was 41 years old and it was repaired five years ago and inspected last year. a visual inspection before it's collapse sunday did not reveal any suspicious damage. they hold hearings on the bridge collapse within a week. he says motorists all over the country ought to be concerned. >> half the bridges in this country are regarded as not safe. half the bridges in new york state are about 15,000, 200 bridges are not safe.

>> the new york governor says it is certain that many bridges will need to be closed in repair. still to come, a busy highway bridge comes crashing down in minneapolis. the horror and the cause. and later, could a high-tech solution warn us of bridge failures before they occur?

>> tonight on a second look the safety of america's bridges. in 2007, the suspension bridge that carried i-35 over the mississippi river in minneapolis collapsed. 13 people died and 145 others were injured. here is our coverage of that day from years ago.

>> reporter: at 6:05 this evening, the entire span of the i-35 bridge came down. it sent at least 50 vehicles plunging at least 60 feet to the mighty mississippi. >> it fell all the way down. i probably had a 30 or 35-foot free fall and there were cars in the water. there are cars on fire. the whole bridge is down, and there was a school bus next to me. we had to carry all the kids off of the bridge. find a safe place to get them off. and it is just incredible. it cannot believe i am even talking right now. >> reporter: cars and trucks were not the only vehicles on the span. a school bus barely escaped the free wall. well intention good samaritans came to help while others tried to contact loved ones who used the bridge. >> it just doesn't seem, it's a

horrible situation, you want to stay out of the cop's way, but at the same time, you want to find out if the person you cared about is okay. i would be happy to know she is hurt just because i would know she is alive. >> reporter: the scene resembles an earthquake, but in is not earthquake country. n if this wasn't a terrorist act or an earthquake or a construction mismap, then what? what could have possibly caused the collapse of a bridge built in 1967? we posed that question to a uc berkeley professor. >> scouring. the water erodes the piers an the foundations of the bridge. that might be a suspect. my guess is there is a combination of factors. maybe the scouring, maybe the traffic, maybe the aging.

i don't think the construction work, but maybe, the construction. probably all came together and created this tragic situation. >> reporter: the investigation into the cause began the very next day even as crews worked to recover some of the victims. ktvu's reni kenp brought it this report. >> reporter: laurie's sister survived but it is hard to see how anyone could have made it out alive when you look at this video taken at a nearby security camera. watch in slow motion as several sections of the 1900-foot long bridge fall like dominoes taking an unknown number of cars with it. the national transportation safety board arrived today to examine the wreckage. investigators will try to see what went wrong. >> we will be examining the

concrete steel and if it in fact failed at any time. >> the i-35 west was the most used bridge in the state of minnesota. there's new information tonight that state inspectors found no structural flaws during examinations over the past two years but engineers from the university of minnesota say say saw signs of trouble years ago. they reported the bridge had structural deficiencies including corroded steal and girders that were distorted. now there is word the bridge is going to be replaced. >> there was the view that the bridge was going to need to be replaced but it appears on the information we have available the time line for that was not immediate or imminent. >> reporter: the bridge was built in 1967 with a single arch to avoid putting piers in the water that may have impeded navigation. tonight, there are questions about the structure's design and maintenance. >> a bridge in america should

not fall down. >> reporter: today, engineers tried to control the flow of the mississippi river at a dam upstream to give divers the chance to look for bodies entombed in cars. they used lights to identify license plates on submerged vehicles but then the river flow shifted and the search had to be called off. many in minnesota are still expressing horror. >> the whole bridge is in the water. everything was down. >> reporter: five month later, the national transportation safety board concluded that a design flaw led to the bridge collapse. steel plates on the bridge were not as thick as they should have been. the board found a heavy load of construction materials on the bridge led to the lapse. investigators said at the time there was no evidence that the

designed flaws went beyond the minneapolis bridge. when we come back on a second look, why an engineer says he night have a high-tech solution to bridge failures. and a bit later, the bay area bridges that are on a federal list of those considered structurally deficient.

>> nearly four years ago, some drivers on the bay bridge got quite a scare when an eyebar broke loose and crashed down on the roadway. it raises the question what can be done to detect problems before they occur? one engineer presented a high- tech answer. here is david stevenson's report from 2010. >> reporter: the daily drive across a bridge in san francisco can be a leap of faith. some saw their faith shaken when 5,000 pounds of steel rained down on the deck of the bay bridge in high winds last

october. >> all of a sudden, the cable and things fell in front of me and i had no idea what it was. >> reporter: an eyebar repair had failed. >> it was very scary. i thought i was going to go into the bay because i drove over it. >> reporter: the eyebar failure stirred memories of an earthquake that caused problems to the bridge years ago. the university of minnesota engineer jerome lynch wants to use high-tech sensors to alert engineers when structures are fatigued like what happened in minneapolis. the project is funded in farther by a $9 million federal

grant including applications like this so-called sensing skin. >> for example, we can place this on the interior of a structure, say on a bridge stack and measure the amount of corrosion occurring on the interior just by reading this from afar. >> reporter: the idea is to deploy these sensors on every bridge to make complex measurements without moneys of yards of cable. >> it is a fairly low cost prototype costing about $100 per node. >> reporter: those collaborating say it will be at least five years before the first generation of sensors are ready for the commercial markets. in the meantime, some of it is being tested out on this bay area bridge. they tested about a dozen wire

licensors. it became a case of too much information. >> the problem with these sensors, it is not only getting the data out but making sense out of it. >> reporter: engineers are using mathematical models to process that data. >> it is complicated because it is a continuous, it is like a kilometer long. so there's almost an infew gnat number of places where you could put a sensor. >> reporter: the idea is to make it simple for bridge operators to understand exactly where the problem is. >> if the maintenance problem says green light or yellow light, that is all they wan to know. if there is a yellow light, they go look over there. >> reporter: caltran says there are already motion sensors on the bay bridge that measure

movement created by an earthquake. officials say the next generation of sensors may offer a better understanding of bridge stress before and during an incident. >> when you have good hard data on what any bridge is going through during an earthquake or during high winds, you know, that knowledge is golden. >> reporter: engineers developing the new sensors say they will be invisible to motorists. >> as far as traveling public, they can be a lot more confident on the bridges that things are being monitor as they move along. as they drive on it. >> reporter: andrea nelson says she welcomes the new technology. last year's incident leaves her cautious about trusting this span again. ingly don't want to cross that bridge. >> when we come back on a second look. the federal government has a list of bridges they consider structurally deficient. we will show you the bay area bridges that are on it. medications?

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look where the topic tonight is bridges and the dangers they hold as they age. last month, david stevenson told us about the bay area bridges that the government has listed has structurally deficient. >> reporter: a smooth highway ride often hides the rough condition of california bridges. >> there are about 2,000 bridges that are labeled structurally deficient. >> reporter: this bridge is in palo alto. it is on a list of federal listed bridges under close scrutiny. >> here, clearly, there are signs that things have been patched over times. >> reporter: but jay seraf is a manager engineer. he says a quick look cannot determine a bridge's safety but it is evident this bridge has been worked on over the decades. the signs of ages are

everywhere including missing chunks of concrete. >> it is clearly corroded. >> a lot of our infrastructure was built in the 40s and 50s so their lives are coming to an en. >> reporter: the average individual of a bridge is 44 years old, but many of these are much older. >> it doesn't mean it is in any imminent danger of collapsing, it just means it is going to need some work of some kind. >> reporter: we visited a number of those including this one on san francisco's third street. the cost to fix it? $23million. there is also this bridge on oakland over the lake canal. it needs $15.6 million for a seismic retro fit.

caltrans gave us only the most general sense of how they prioritize the projects but the major projects get the priority and the dollars. the $800 million demolition on the other hand replacement of san francisco's earthquake vulnerable doyle drive began last year. thousands of cars used it each day to get to and from the golden gate bridge. >> traffic levels are something we take into account. how many people use this on a daily basis and how necessary is it for it to remain open? also the age of the structure is important. >> reporter: important because the environment from the salt water to the shifting earth takes its tolls on bridges like this one. >> you see some cracking up at the top and horizontal cracking here and the whole thing seems to have come out maybe a little

bit and also the vertical crack. the separation of the bridge and the wall on the side. >> reporter: and the damage and danger isn't always below the bridge or on the roadway. sometimes, it is high over head. this road bridge is getting a bart airport extension grafted onto it but the bridge is 45 years old and you can see where chunks of concrete have fallen down posing the interior. with the economy recovering more funs, they might get to put new tread on these old bridges. >> and that's it for this week's second look. i'm julie haener, thanks for watching. to watch tv someplace else, we'd have to go to my aunt sally's. have you ever sat on a plastic covered couch? [ kids cheering ] you're missing a good game over here. those kids wouldn't have lasted one day in our shoes. [ male announcer ] add a wireless receiver. call to get u-verse tv for just $19 a month

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>> dick: you definitely can hear the wind howl. i mean, it's loud. >> hawkins: it was like a wild river. you got two- and three-foot waves that are rolling over you. that's when i knew we were going down. >> matt: when you see your neighbors' houses just float away... >> duerstock: we wanted to leave right then, and we couldn't do anything about it. >> hawkins: i thought all of them were dead. there was not a doubt in my mind. >> announcer: this is 'storm stories.' [ thunder crashes ]