Philadelphia I-95 Bridge Collapse Explained

[@PracticalEngineeringChannel]

🌌Get Nebula using my link for 40% off an annual subscription: go.nebula.tv/Practical-Engineering 🛠What engineering disaster would you like to see me cover next?

[@davidneel8327]

Train derailments which seem so frequent now.

[@pierrecurie]

@@SomeGuyCalledJ ????

[@VapidGhost]

minneapolis i-35w bridge collapse

[@bradsimonelli3013]

Hey there! Love your videos! I was wondering if you could do the rebuilding of the tunnels in Boston? I’m curious what’s happening because they came out with the construction and the start really quickly! Thank you!

[@fredashay]

Sounds to me like tanker trucks need to be built to better standards to hold up against a crash.

[@Fjalll]

I appreciate how many times you managed to vary how you said "A tanker collided with an overpass"

[@443DM]

I was expecting him to say the next one wasn't a tanker that collided with an overpass, but "a fuel-barge collided with a bridge tower and caught fire"

[@General12th]

"That time, an overpass collided with a tanker."

[@CalculatedRiskAK]

A propellant relocation vehicle made contact with a separated roadway crossing.

[@Nibsipipsi]

@@CalculatedRiskAK fuel is not the same thing as propellant.

[@bcbeasters]

And then yet again, but this time in Milwaukee (which is Algonquin for "the good land") another Lot Lizard Transport Vehicle... wait for it... crashed into a bridge. 😁

[@evanr.2586]

I live just outside Philly. There's one reason that the gridlock didn't occur that isn't getting much coverage. Real-time traffic routing. Turn by turn directions from phones and GPS didn't just blindly offer official detours. They adapted to real traffic in near real time. This let the flow spread out to minimize resistance like water through a maze. Traffic could utilize the entire regional road system to re-levelize.

[@monkeyoperator1360]

hopefully the GPS is more reliable in the cities than it is outside the cities where it is terrible at routing people and takes people down private drives, and private roads

[@barbeerian]

Despite all that, every time I went through it, North or South, GPS routed me right through the detour.

[@ryanm2628]

@@monkeyoperator1360 I guess it depends, but I've personally never had that problem anywhere in MN, rural or urban

[@Varangian_af_Scaniae]

Yes let them surveil you everywhere!

[@dxb338]

@@monkeyoperator1360 we dont really have private roads in philadelphia, or not many. The issue you are far more likely to run into (using google maps at least) is being told to make a left turn when there is a no left turn sign and no turning lane, or a right turn at a "no turns" intersection. People already drive pretty lawlessly here and tend to do whatever they want, but i know for fact at certain intersections drivers are blocking the left lane or unsafely cutting across oncoming traffic because their GPS is telling them to.

[@elijahm3688]

I really enjoyed the bit where you go over why the bridge repairs can get done so fast (and why other stuff usually doesn't). In just a few words - "fast, good, cheap. pick two."

[@WyvernYT]

...and often only one.

[@Mr.Sparks.173]

And so, so many managers, bean counters, and clients like to act like they get to pick all three

[@amosbackstrom5366]

You can't have your cake once you've already eaten it

[@ZacharyRGrant]

WYOTK

[@Lohanujuan]

Wouldn’t they pick fast and good? I think it would be “pick one”

[@Korvanick]

I love that you and Road Guy Rob are friends! His channel is severely underrated and deserves more attention. Great video, as usual.

[@PVS3]

One element I'm surprised you didn't discuss: A tanker fire is a destructive BEAST. Designing around something like that just seems prohibitively expensive, especially given the rarity and isolated nature of the risk.

[@harddiskwp]

Well, there are (relatively) cheap measures to prevent large fires under bridges in the first place: guard rails to prevent vehicles from crashing into the walls (and staying there as a result), lane direction separation to prevent head-on crashes, and education of drivers to not stop under or on bridges and in tunnels even if their vehicle is on fire. The latter is the most important - even if your vehicle is actively on fire, the wind keeps it relatively contained but once you stop, that effect will vanish and the fire will outright explode in intensity. This is also why, at least in parts of Europe, trains in high-speed train tunnels need to have emergency brake override systems in place.

[@clonescope2433]

​@harddiskwp Well, a lot of these bridge collapses in the U.S related to fire happened on interstates, which are divided roads. I would be very interested to see what the Department of Transportation has come to the conclusion of the cause of the accident that led to the fire. Because 1 or 2 times is a freak accident. But when it seems to be happening once every year or 2, something may be going on outside or just the design of the bridge and the roads.

[@PVS3]

@@clonescope2433 There's a bit of a black swan effect here. Extremely rare events become more common as you expand the number of opportunities. 50 thousand miles of interstate and (according to BTS) 590,000+ highway bridges - even a 4-in-a-million chance would result in about 2 per year. (Very slim odds) X (Half a million rolls of the dice) = a high likelihood of event SOMEWHERE. But, reinforcing half a MILLION bridges is incredibly costly and would be more disruptive to traffic than the rare fire event. So the reasonable thing is to make them safe against more common issues and plan to quickly rebuild when needed.

[@jerryhogate3640]

I am a truck driver in the Philly area, it was a nightmare and the listed detour was a route(I-676) that is a parking lot on the best of days. I can vouch that the economic effects were pretty crazy.

[@frankrizzo7454]

i95 is a parking lot between Academy and Girard every morning when the road is working.

[@adde9506]

I drive a bus into the city all the time, drives me absolutely bonkers that google maps doesn't have weight and height restrictions on it after all this time.

[@geniferteal4178]

​@adde9506 i think it's the dumbing down of the job which, for the most part has already happened. The more information you provide someone to be able to do the job, the less they have to know. They are increasingly relying on these automated systems and not their own experience and knowledge and then you get what you get for drivers. I haven't used a local taxi in a while. Never an uber on my own. I called a local taxi to take me less than a mile from the train station. I was arriving at. I said I'm going to the dentist from this intersection. About 3 blocks north. They said, what is the address? I said I don't know, it's my dentist. They said we need the address. I said, Its only 3 blocks from this major intersection. I've been going there for twenty years.I never knew the actual address. They said call me back when you know the address. I was frustrated to say the least. For the first time ever, I had to google my dentist and find the address just to provide it to the taxi driver. I realize the taxi driver likely didn't understand english and who knows what other limited knowledge they had. I think this guy might have really understood our conversation, but that's besides the point. The job had been dumbed down to: go to this dot on. the device will tell you how to drive. Is that what's happening to the trucking industry? What is our fail-safe when those devices are wrong or incomplete? What other information are the drivers potentially at risk of getting wrong?😢 I don't know a whole lot about the trucking industry.But I believe many years back there was a time when truck drivers might have been considered the most knowledgeable drivers on the road. Could this changing demographic of truck drivers be contributing to these type of incidents?

[@jensschroder8214]

The same happened in Germany on September 17th, 2020 on the A40 Autobahn. A tanker truck burns out under a bridge. The bridge was then demolished and rebuild. And that in the most populous area with the highest traffic volume. A main railway line runs over the bridge and also had to be closed. The replacement buses for the trains had to drive under the bridge.

[@iaadsi]

Nice example of a literal single point of failure.

[@neurofiedyamato8763]

Dang that is crazy. Just funneling everything on that one area. I feel that from a city and transportation planning perspective its a bad isea even if it didn't catch on fire. If there was a need to evacuate, people would funnel through that single corridor.

[@Genius_at_Work]

@@iaadsi Sort of the same Thing happened in Hamburg, but with a Metro Overpass. You might be not familiar with the Geography of Hamburg, but the City is literally divided into two Parts, that are separated by a River instead of a Wall. The River can be crossed at two Points only; a Highway Tunnel which has terrific Traffic Jams 24/7, and a Set of Bridges that carry another Highwayand a major Road, both with serious Congestion too, plus Metro Rail and Mainline Rail. That Metro Rail is the most important Way for Commuters to cross from one Side to the other, and it was interrupted for about a Month until the affected Overpass was fixed. Btw. talking about Single Points of Failure, Hamburg also is the only "Gateway" for Rail into the northermost Regions of Germany and then further on to Denmark and Sweden. The Rail Line going through Hamburg is the most congested one in Germany, and 20+ Minute Delays because Trains are "stuck in Traffic" are regular. That Line was down for three Days last Year, after a Data Cable for Signalling was destroyed in another Fire last Year. Until a few Years ago, there used to be three Cables for Redundancy Reasons, until some smart Manager realised that Money is wasted on three Cables even if one can do the Job just as well. That three Day Interruption completely cut off northern Germany from the rest of the Country, also brought Regional Rail inside northern Germany to a near Full Stop, cut off Denmark from Mainland Europe and Trains to Sweded had to divert to a Ferry. All of that because some Manager wanted to save a few Bucks that were "wasted" on Redundancy. IIRC, both of these Incidents happened last Year, or maybe in 2021.

[@iaadsi]

@@Genius_at_Work That sounds very similar to Prague, which is also split down the middle by a river (Moldau) with very few high capacity bridges/tunnels forming natural choke points. Prague is at the center of our star-topology highway system, so virtually any two places in Bohemia are connected via Prague. The ring road is incomplete so lots of transit traffic literally has no other option but to punch through Prague itself, right by people's apartment windows.

[@MartinMeise]

This video instantly reminded me at that incident, as I live close by. Good that you mentioned it. I would be interesting if there is a public investigation report available.

[@Schenkel101]

Feels good to hear about topics like induced demand and varied transport infrastructure not only from urban planning channels, but from an engineer, even if only in passing.

[@aemmelpear5788]

I also really appreciated that he mentioned it.

[@coreyw427]

Induced demand is mostly a nonsense. It’s really just demand. It’s like saying building a new hospital - which are generally quickly overwhelmed with ‘new’ patients almost immediately - is pointless since we have now just created more patients. The reality is that the new hospital has caused more people to present for treatment because the wait times are now marginally shorter, just like a new road enables goods and people to be transported marginally quicker which results in the quantity of vehicles increasing. Both are just demand that already existed at lower ‘prices’ - of course the new hospital had not coursed more people to get sick or injured.

[@nicolasgrothey4014]

@@coreyw427 Not a great comparison. The idea is that we want congestion to go down. Less traffic = Less idle time. So the previous attempts at adding lanes to reduce traffic don't work because as you hinted to people on other roads/different modes of transport will switch to the expanded highway... this leads to more traffic. Now we're right back where we were but hundreds of millions in the hole. The goal of a hospital is to treat people, the goal of a highway shouldn't be to have traffic.

[@coreyw427]

@@nicolasgrothey4014 The goal of a highway is literally to allow people and goods to be transported, as Grady mentioned earlier in his video. That’s what traffic is.

[@ChristopherLuongo]

@@nicolasgrothey4014Yes, the goal of a highway indeed is to have traffic. Hopefully not congested traffic, but moving traffic.

[@fieteferrum3032]

Additional ways to reduce the risk of fire under bridges: 1 Better working conditions for truck drivers. 2 Better maintenance of trucks.

[@weldonyoung1013]

You could also add, higher training standard for tanker drivers. Those liquid filled or partly filled trailers can be unstable. Fluid slouching is very common. Come to think of it, better roadway/highway markings would help.

[@jdaayhan5159]

Ottawa is currently replacing all of it's highway bridges (and has been for a few years) and the replacement itself usually takes a little over 3 days. The next replacement starts August 10th and is usually live streamed for those interested.

[@ToughCanadian]

Crazy, we just had something similar to this happening just outside of Toronto Ontario, Canada. They deemed that the bridge was okay, so far it's still standing.

[@II__argo__II]

where was this and which bridge? I don't recall hearing about it

[@thediamondtree]

remember the bridge (highway 8) that washed away due to the bad flooding in 2021. The impact of that was tremendous and was felt all the way on the east cost as that connects Canada to one of the biggest ports. Shows how our infostructure in Canada needs to be updated and "fool proofed".

[@snakesonn]

Canada SUCKS

[@JackReacheround]

@@II__argo__II near pickering i think, it was a few weeks ago.

[@timmccarthy9917]

I'm glad you added "Ontario Canada" or I'd think you were talking about the other Toronto

[@ncc74656m]

Exact same thing happened in Yonkers, NY in 1997. There was a turning lane that looped back under the underpass for I-87 which had been known to be dangerous and a serious risk for decades, but had been left once it was built. One day a tanker truck made the turn and was hit by a car coming down the road that formed the underpass. The truck sprung a leak which quickly turned into a fire, and it destroyed the overpass for I-87. It ended up taking about 5 months to rebuild in an emergency contract, and that turning lane was removed, as there was another not a block away controlled by a light already.

[@jimurrata6785]

There's also the 1994 Grant St overpass on 287 in White Plains. Propane tanker took out that whole section.

[@iaial0]

​@@jimurrata6785in august 2018, near Bologna Italy another propane tanker rammed into a line of still vehicles. Probably the driver had a stroke or fell asleep. The explosion's fireball was 100 meters in diameter and brought down the overpass it was on. There were 150 injured because of the debris. The highway ran over some residential area so there were plenty of shattered windows

[@supertornadogun1690]

@@iaial0 Good old fashioned BLEVE.

[@iaial0]

@@supertornadogun1690 correct, footage from the cameras could be used by manuals for demonstrate a BLEVE

[@billysolhurok5542]

@@jimurrata6785 was that the one where the tank 'cylinder'broke from the chassis and went like a rocket ,through someones house?

[@orwellwasright9604]

tanker trucks, the natural enemy of bridges

[@davidsloat1016]

Interesting question... seems like EV batteries burn as hot will we eventually see EV fires be as dangerous to bridges?

[@grn1]

@@davidsloat1016 I honestly thought the same thing. I'm all for EVs but we do have to consider the risk and rewards of any technology. Fortunately EV fires are extremely rare, at least with more reputable brands (not cheap Chinese* ones) and assuming someone doesn't poor gasoline all over them (at least one of the big EV fires that got a ton of coverage as proof about how dangerous they are was caused by vandalism). * China is actually capable of making high quality stuff for an appropriately high price but they are also perfectly willing to make low quality stuff for a lower price, it's not hard to guess which option most US companies go with.

[@billykyle]

Great video. Thanks so much for using my drone video! I’m happy it can help highlight this event.

[@blakem.trimble9942]

Side note; as a DOT intern, we got a notice about what happened in an email. They mentioned some materials stored under the bridge were flamable and we should be careful to not do that anymore. Hope this little insight may have been helpful

[@pyronixe]

Snitch

[@joelmichaeleo]

Industrial-sized Sabotage: EXPLAINED

[@blakem.trimble9942]

@pyronixe Most public agencies will fulfill public record requests, I just commented what I knew, to possibly share some insight. You're welcome

[@dboi1656]

I don't know why it's so entertaining to me, but it's such a funny idea of getting an email that in effect just says "Hey guys, they did a thing that nobody would consciously do because it can break things. Don't."

[@The_Quaalude]

Why tf were flammable materials stored under a highway bridge? 🤔🤨

[@adriantombu]

I was living in Rouen, France when the bridge took fire (and sadly I was using it everyday to go to work). It was fun seeing the bridge transported by a barge on the river to be repaired in Belgium. It made for some once-in-a-lifetime pictures.

[@metrazol]

The foamed glass is such a cool material. I was on a project where they used it to fill a rooftop beer garden on an office tower. Guys were hauling giant bags with their hands, but you could walk on it no problem.

[@westrim]

Thanks for boosting Road Guy Rob! I started watching his videos a few months ago, and I like how he gives a balanced, ground view of the urban design and planning stuff and its effects, positive and negative.

[@Croz89]

I think he provides a suitable counterweight to the mostly transit and active travel focus of other channels on transportation infrastructure. Road infrastructure needs some love too.

[@bobmckenna5511]

I am so impressed the vendor kept live feed of the repairs. An additional task, but other communities might benefit from this. Brilliant.

[@danajorgensen1358]

Philly is the gift that keeps on giving! Did you know that ANOTHER bridge on I-95 further south in Philadelphia just had huge chunks of it fail in the last few days?

[@cr10001]

A classic instance of a fire on a bridge was Robert Stephenson's historic Britannia Bridge across the Menai Straits from Wales to Anglesey. Finished in 1850, it had twin wrought-iron box girders through which the trains ran. Part of the corrosion proofing was by tarred hessian (we'd never use that today, but it lasted 120 years). 120 years later, it caught fire (kids probably playing with matches). Though the tubes survived, the fire destressed them and impaired their load-carrying ability. The tubes have been replaced with a double deck on steel arches using the original piers and abutments.

[@EcceJack]

"tarred hessian" definitely sounds like someone just trying to make a very flammable material for fun xD but I can appreciate that it was a good solution for the problem at hand

[@kuromameshiba4418]

@@EcceJack Sounds like a metal band. Let's make this happen, people! 🎸

[@somethingelsehere8089]

Hessian = burlap

[@stanley3647]

But railway line was rebuild as single track. And road is only single lane each direction. ... So, instead rebuild this bridge properly, and build another full size bridge for heavy traffic, this weird hybrid was created, and today there is huge bottleneck at network for trains and cars, for this important route to port at Holyhead.

[@markedis5902]

Worth looking at tanker safety and why they crash under bridges so often.

[@iluomopeloso]

That's probably what the NTSB is primarily focusing on.

[@DrSkrungle]

We are under attack

[@randomuser5443]

Because we dont ask about trucks on fire in forests

[@matthewerwin4677]

Trucks crash everywhere all of the time. We only hear about the bad crashes that take out bridges.

[@KSCPMark6742]

Tankers crash and burn all the time, you just don't hear about it, it's not news. An exit like this under a bridge is relatively narrow, curved and constrained. A likely spot to lose control.

[@allanszast7579]

Same thing happened on I 95 in Bridgeport, CT some years ago. Army Corp of Engineers had a temporary bridge in place in 4 days.

[@musewolfman]

And then again on the Gold Star Bridge in Groton just a month or so before the one in Philadelphia. Fortunately that didn't end in a collapse, but it still shut half of I-95 down until inspection could be performed.

[@allanszast7579]

@@musewolfman I forgot about that one

[@Polygonetwo]

What you said regarding cities being a lot of tiny decisions adding up to one big, beautiful thing is why I adore colony management or city building games. You get to watch in real time and help shape the tiny details as things progress into something completely unique. Sure, the pieces will be the same, but the layout will always be different depending on what you happened to need most at any given moment during the process.

[@noemierollindedebeaumont1130]

Yes, seems like Cities Skylines 2 will be awesome from that point of view !

[@SanderGroenendijk]

Thanks!

[@MichaelfromtheGraves]

Fortunately Philly has one of the better regional rail systems in the county and was able to add more trains. Amtrak was able to accommodate some other longer trips. We have a long way to go to reach global standards of public transportation but this could have happened in a much more vulnerable location.

[@masterbond9]

Amtrak owns the rails in the area, i think

[@namAehT]

We need to expand our long distance rail. Right now it's a $100 7-hour train from Philly to Pittsburgh, a full 2 hours longer than driving assuming there are no delays (which are common), there's only one a day, but accounting for gas and tolls it's about the same price as the Turnpike. Most of the problems stem from the fact that freight companies own and "maintain" the rail and often claim priority over Amtrak even though passenger trains are _supposed to_ have the highest priority. If it were a _guarenteed_ 7 hour trip and there were more departure times then it would be worth it to take the train IMO.

[@nonsense402]

If this happened in Omaha, NE, logistics companies would be pissed as that's a major transportation artery where detours add significant cost to that leg of the trip. A lot of line hauls run through I-80, and with its proximity to Offutt AFB, I wonder what the responsiveness to this would look like.

[@eldenfindley186]

@@masterbond9SEPTA owns most of its own rails

[@volodymyrzablotsky5372]

Problem was for all the trucks that had to use the local detours that were just too large

[@hgbugalou]

The recovery from this event was no less than miraculous if you are aware of just how road construction can take. The contractor and PenDot should just a lot of credit here for out of the box thinking and stellar execution. I am sure the permanent structure will be up in no time.

[@KSCPMark6742]

"miraculous"..? That's like thanking god when a surgeon saves your life.

[@thepimpyoda]

Have you seen 83 bet it takes a year

[@RCAvhstape]

@@KSCPMark6742 This is Philly we're talking about here. Trust me, it's a miracle it gets done at all, let alone in 2 weeks.

[@michaelomalley8814]

Great video as always. Loved that overhead shot of I-76 at night. I took a very similar photo earlier in the summer myself. Side note: I am the person that literally recorded the traffic volume, which allowed PennDOT to provide the 150,000 vehicles/day statistic. Feels kinda cool to see how many times that number has been used to emphasize the importance of this single bridge outage. Keep up the good work!

[@Abihef]

This is awesome, because of watching your videos over the past years I understood everything in depth about the temporary embankment and it's construction. I've always been super grateful for your channel learning me so much I need to know for everything I plan to construct in the future but it was also awesome to see this and realise how much I've learned from you. Just about everything that came to pass in this video I could fully understand or already guess because you've thought me so much. It was like coming to class not expecting an exam and passing with flying colours. Don't know if I've ever thanked you for the knowledge and these awesome videos but if I haven't I'm doing so now although I can't thank you enough.

[@61rampy65]

I'm not what you would call a regular viewer, but I have watched a number of Grady's videos. His videos are always enjoyable, I learn something new, and he has such a pleasant way of discussing things. No different here.

[@billbeyatte]

I didn't know how I-95 was reopened so quickly. Thanks.

[@SuperLuminalMan]

7:30 For the comparison between fire and earthquakes for collapse probabilities, fires can be 'controlled /s' from external sources E.G. regulations for safer tanker trucks. But earthquakes cannot me pre-emptively mitigated, only predicted, and then in a limited sense. If fire is less prioritised in the design codes that might be the result of expecting better safety from other professions, or an over emphasis on more probable failure modes (hydraulic scour) at the expense of the improbable ones.

[@ladyeowyn42]

Additionally, after an earthquake emergency response is overwhelmed (containing fires and treating the injured). Seattle has 1 major route that goes north to south and east to west that’s seismic rated expressly to allow emergency services to do their jobs. And it’s not the interstates, it’s Aurora and 520, and both needed major remodeling to make sure they’d survive a mega thrust earthquake.

[@Beryllahawk]

It's insane thinking just HOW complicated it really is to even analyze a fire like that. So many factors and so many questions, and all of it on top of political and economic calculations? Yikes.

[@bryansmith1920]

Why should making sure it never happened again stop because of costs, That's so wrong, Do you have a loved one, How much would you sacrifice to keep them safe, that's the reason capitalism doesn't work in a world full of Human beings, We need another way and it's NOT communism,

[@nerdy1701]

​@@bryansmith1920like it or not, life is not completely safe. There is always going to be a point where the cost tips to not being worth it and finding that point will always be a challenge. That stuff has to be shipped somehow, everyone uses it.

[@rationaldemon195]

@@bryansmith1920 Its not only costs that stops a project there are more and many more factors, as inovation comes there will be better,faster and safer ways to deal with the situation, as engineering its all about taking all the information you can and find a solution to it in the most efficient way, cost is only the tip but there are alot intricate moments, that making a project can take time, training, and resources to accomplish a project, safety is also taken to account when trying to build such a structure and then you have to consider its risk of building a structure then you have time estimation for a project to finish. There are always going to be hindsights and as time passes on we will learn something new about it, its just feesibly unreasonable and unfathamable to make a structure that is 100% proof against everything, you can cover so much ground but there will always be a design flaw.

[@h8GW]

@bryansmith1920 We don't build pedestrian bridges because of costs, even though it's certainly safer than having a crosswalk on an 8-lane arterial road. Dead pedestrians tend to be poor people, after all.

[@KarltheBarl]

@@nerdy1701is what it is attitude let’s you be exploited without noticing

[@alexanderboulton2123]

This collapse is the single greatest argument for public transit that a person can make.

[@bullettube9863]

You would think that a bridge made of concrete wouldn't burn, but it's the steel beams that cause the collapse. Steel expands when it gets to 400 degrees F and this expansion will pull the concrete apart. People think that steel fails when it's red hot, but as a former welder and fabricator I can tell you that 400 degrees is all it takes to bend the steel into shape without it cracking. Coating the steel in concrete will not work as the steel will corrode inside the piers and supports and fail when you least expect it. Concrete barriers designed to deflect vehicles away from the piers works if there is room made for them. But a fast moving tanker can easily jump right over them when it jack knives.

[@JasonWMorningwood]

There is only one solution to this problem, forbid tanker trucks from catching fire in collisions with overpasses. They can't catch fire if you tell them not to

[@AlexandreMacabies]

Thanks Grady for including that important reminder on car dependency and induced demand. I was screaming at my screen from all of those grid-lock drone shots. Maybe the impact of highway closures wouldn't be so bad if cities were designed to be more accessible without every single citizen needing a 2t steel box for their daily commute.

[@IngeniebrioCivil]

You can also use high density polyesthirene ("geofoam") as backfill. I've seen been used as backfill under approach slabs before bridges in low bearing capacity soils.

[@mastheadmike]

I live in the neighborhood just before the incident and am stoked for you to touch on my local news! Been following you for years and actually thought of all the civil engineering going on as it was deconstructed and then reconstructed!

[@BertVerhelst]

10:57 if you make a video about how they did that project. Or what they do during accelerated construction. I would watch that.

[@robbloforese]

Always love your videos - back in 1973 we had a freighter called the Sea Witch collided with an fully loaded oil tanker Esso Brussels just above the Verrazano-Narrows Bridge - resulting in an intense explosion and fire directly under the bridge. Had the chance to survey the Sea Witch a few years later while working at Sea Train shipbuilding and its 1 inch steel plating was twisted like melted plastic. After watching your video I wonder if this fire affected the bridge structure at the time? thanks.

[@noahheadley1337]

Speaking of Philadelphia civil engineering mishaps, it would be interesting to see a video on the pump failures on 676 a couple years back that turned it into a river.

[@ericpaul4575]

One of the biggest slowdowns for construction projects is the cure time for concrete. It must cure long enough for it to be strong enough for the desired loads. This can take 30 days or more. So at times there is a fury of activity to do a concrete pour then a long wait for the cure to complete enough to do the next step. If the project is large enough then these wait times can be staggered, but on smaller project like a bridge of a two lane highway, there may not be a way around the waits.

[@nvelsen1975]

There isn't. In the past they used to add chemicals to concrete to make it set more rapidly. Well, that's the reason all houses here need a 20-50K concrete replacement in their flooring, because half a century later it's already coming apart rapidly with repairs starting as early as the 1990's (so roughly 14-19 years after pouring)

[@richardross7219]

We had a similar fire in CT many years ago on I-95. They were able to use temporary bridges for a while and then did a weekend replacement. Good video. Good Luck, Rick

[@robster7787]

Listening to the sequence of him listing multiple bridge incidents reminded me of that song. “I crashed my car into a bridge” “I don’t care” “I love it”

[@briangarrow448]

Many years ago I worked for a small city public works department that had a small crisis when a single access road slid during a major storm event and stranded about 40 homes without any access for emergency services or other vehicles. The solution that was chosen because the soils couldn’t handle the loads of normal rock fills was wood chips. Yes, wood chips. 30 years later and the road is still open with minimal settlement. I’m not sure if this repair will last another 30 years, but for a emergency repair I think it’s done a fair job.

[@kenbrown2808]

you're lucky. in my area, the main highway into town had a slide, and the repair was carried out with wood chips. for the first few years, the road would be venting steam through the cracks that formed as the chips settled. now things are stable enough that they only have to repave the section a couple times a year.

[@nightshadelenar]

i'd say that's lucky for that cheap of a repair, though i am sure it will be seeing replacement fairly soon.

[@kiwikeith7633]

I recall a wool-store fire around 1963 in Wellington NZ. It was a large building of RSJ steel frames. All trusses sagged to ground level during the fire. I recall that it was pointed out that laminated wooden beams would have stood longer against heat. As Steel is heated, its strength abates, and can end with it melting. So Bridges have structural steel elements which can weaken with heat.

[@goodbyemr.anderson5065]

Well in case you didn't know wood burns at a much lower heat, and also loses its strength.

[@kaitlyn__L]

@@goodbyemr.anderson5065laminated timber scorches the outside which protects the inside, and it keeps rigidity until it gets hot enough to burn the core. They said last longer, not never fail.

[@goonies_never_say_die]

There is a field of engineering dedicated to studying fire as a hazard but there are only a few schools in the US that offer fire protection engineering programs, University of Maryland and Worchester Polytechnic Institute in MA. There is also a Society of Fire Protection Engineers. The fire protection community has studied bridges, tunnels, and other structures extensively but like you said sometimes arguments can be made to limit how much protection is warranted.

[@noway5976]

I was going to room with a guy back at Univ of MD who was fire protection engineering. Good guy with good grades (helped that his previous roomie was a math major 😂) He had a job lined up and waiting months before graduation. Took a job for $50k/year in St Louis instead of $75K on an oil rig in the Gulf of Mexico. This was in 1988, 35 years ago!

[@vinnylamoureux1187]

I live in Atlanta. Bridge out was a nightmare. God bless the clever contractor who got it opened so quickly. He was well worth the reward he was paid for his innovative solution. Still, I hope we don't need him anytime soon. Great video as usual. Thank you.

[@outistynnanyt5153]

One of the major LAX runways has a decently long underpass tunnel, well, under it. Its a 6 lane, 1/3 mile divided tunnel. It honestly might be worth a video?? I feel like theres a lot of interesting engineering constraints on a car underpass that goes underneath an airport runway holding 2+ Jumbo jets taking off at a time?? Anyway!! Theres signs approaching both sides saying something along the lines of "trucks transporting flammable or hazardous materials must use detour." It logically made sense that you wouldn't want a fuel tanker crash underneath a MAJOR runway. Watching this video, it makes even MORE sense.

[@Droidman1231]

I lived in Atlanta at the time of our interstate collapse and saw the amazing work they did to do a full rebuild in only a month and a half, for six sections of 5 lane interstate! I assumed Philly would do the same, but they are not apparently. I'm curious to see how this partial but even quicker reopen works compared to if they rebuilt the whole thing ASAP.

[@shopshop144]

This temp fix got 6 lanes opened in less than two weeks, and left room for the final bridge to be built in different phases. The final construction will take much longer than a couple of months, but the underpass that is now blocked off only served north bound traffic, so I doubt that closing it for a year +- will make too much of a mess. Apparently there still are questions as to how much damage the vertical concrete walls that supported the collapsed bridge section received, and if that too needs to be replaced it will add time to the job, as now part of those walls are buried by the temporary fix.

[@KaitouKaiju]

ATL drivers are so hard on the roads the city's gotten good at rebuilding them

[@justjoe942]

You have answered so many questions I've had over my sixty years. One of my favorite episodes: the workers are not just standing around being lazy, it has everything to do with safety. Thank you.

[@WolfSeril107]

If you haven't seen it, he has a video dedicated to that topic from a few years ago. It's a great watch and covers a lot more points than what he mentions here.

[@J.C...]

Dang it. I guess I missed that part. Time to watch it again 😂

[@deadfirefighter]

I’m a disabled firefighter and you mention the heat from convection and radiation but don’t discount conduction and time. Since most of those bridges have concrete walls/ supports for the steel I beams. As that concrete heats up it also weakens and to get spalling and cracking. Based on the image of this collapse it appears it failed more at the end than in the middle so the failure might have been the vertical segments of the structure instead of the horizontal ( steel) structure. But as I just mentioned time is also a factor. That concrete holds the heat far longer than the steel structures once the heat source ( fire) is removed (put out). Those I beams are designed for load but the thickness of the steel is also determined by a limited period of thermal loading. However, the concrete vertical structure acts as a thermal “battery” holding that heat longer and conducting that heat to the steel above it. Because how long heat is held against steel is often more of a factor in weakening it than how much heat is applied ( based on ordinary materials burning and excluding non ordinary materials like thermite) the areas near such vertical structures are the ones most likely to fail. They become the weakest spot in the steel structure because in addition to radiation and convection they are also subjected to conduction, the weakening of its vertical supports, and because the heat will continue to be conducted to that area after the fire is out. When I left the fire service in 2004 there wasn’t a standard on fighting bridge fires so there may be new standards, but if the bridge hasn't failed once the fire is extinguished firefighters stopped dumping water on it. There wasn’t studies to determine if it was better to keep hitting the tunnel walls with water to cool them to reduce the long term thermal stressing of the steel or if the cooling the concrete in this fashion would cause increased spalling and cracking causing the vertical part of the structure to fail. It’d be interesting if someone is investigating this question I to see you make a video on their investigation.

[@Georgewilliamherbert]

There have actually been two fires in the Oakland Maze; one liquid fuel tanker that collapsed a span overhead, and an earlier incident where a propane tanker hit a pillar on the southbound 580 ramp through the interchange. The pillar and overhead ramp still have the scorching from that, but they were able to test the steel and it hadn’t been heated hot enough to lose properties significantly. It’s more closely inspected now but has held up fine. That’s a good example of the difficulty in figuring out what to protect and how. Two similar accidents at the same interchange and one has had little lasting impact and the other collapsed like I-95.

[@nadapenny8592]

Watched them rebuild this thing on live feed. Incredible work by the builder, really amazing stuff.

[@BradyTCG]

Interesting topic! As a structural engineer, I'm interested to see if a new code book or addendums will come out soon. I was actually stuck in the traffic when the I-65 overpass in Tennessee was burned. The hour and a half drive turned into at least a 4 hour drive.

[@DEATHBYFIRE09]

I came in expecting a post mortem of the failure, and got something better. Great video as always, I hope when we get a full report from the NTSB you can produce a follow up.

[@KSCPMark6742]

There'd be nothing new, the scenario has played out many time and has been analyzed many times. Heat damages concrete and weakens steel. This was more of a look into the importance and complications of infrastructure

[@kenbrown2808]

I was also hoping for an explanation of what fire does to "noncombustible" structures; simply because it is just a larger scale version of why the WTC collapsed because of the fires inside the buildings.

[@alexZWL]

Love this channel. It's my job to inspect infrastructure. Had last year my first bridge, in 13 years that was affected by a car fire. Concrete and fire are never going to go well with each other. The steel rebar looses the needed strength and the bound water expands so it will break the concrete structure. The only thing that i know of to prevent accidents is to create a flame resistant layer that gives you time to evacuate the tunnel or parkinggarage. The other option is to prevent cars from crashing in the first place. In the Netherlands i have only seen the fire protective layer in tunnels and big aqueducts.

[@patrickbuick5459]

Am I right that you are essemtially describing spelling from the water vapour pressure?

[@lucj1410]

Thanks for the insight - it seems the creator was disingenuous in saying the collapse would be "explained"

[@alexZWL]

@@patrickbuick5459 not exactly. Between 150°C and 180°C the calciumhydroxide in cenent loses water. Because of that the cement loses it's bonding capabilities. This occurs in the first few minutes. When the outer layer of concrete is gone the rebar is directly subjected to the fire. Above 250°C the concrete loses permanently some of its compressive strength. Above 450°C the strength is reduced by half. (English is not my first language so this technical stuff is hard for me to translate) In my original reaction i did indeed say expansion. I have looked it up in my study material for the exact explanation.

[@patrickbuick5459]

@@alexZWL Thanks, that explains a lot. I'm no materials expert nor civil engineer, only electronics engineering technology and some pre-engineering, physical chemistry etc. Yes, I am a generalist, as I also did medical studies and work as wellnas music. Your English translations seem to be pretty spot-on.

[@THEBACKSTER]

I remember the 2013 explosion very well, my class trip had to be detoured, the trip was to Phit

[@pravoslavn]

Sir Grady, Chief Engineer, Excellency: Everyone tells you about how excellent your content is, so let me shift gears and tell you how much I appreciate your VERY professional manner of presentation. You speak in complete sentences (subject, verb object.) You never ramble. You know where you want the presentation to go, and you get there. Your discourse flows methodically and is not simply the narration of a "stream of consciousness." And best of all, you do not lard up your presentation with those dumb, ignorant UH's and UM's. (After 7 or 8 of those things, I usually turn off a You Tube presentation.) It is a pleasure to listen to you, Good Sir ! Keep up the good work. -- /s/ Harrisburg ☺

[@stankaliski]

Another great video 😁 I would imagine that the fuel tanker was full or near full. The unabated burning of hundreds of gallons of fuel could heat the steal underlying the road deck beyond its critical temp and the weight of the road deck not to mention the weight of the steel itself would cause it to deform and collapse. One of the pictures of previous taker fires showed the beams deformed into a U shape. This reminds me of of the world trade center in the sense that you can do all you can to make a structure withstand a fire but when you introduce the level of structural damage that occurred and thousands of pounds of burning jet fuel to the mix, structural failure is almost a certainty.

[@inzanozulu]

I don't know if it was intentional or not, but hearing "Devin from LegalEagle is really a liar!" got a giggle out of me

[@broad_cat]

I had to go back and catch again too haha. Roasted him like a diesel tanker does a bridge.

[@C4uSt1CO]

@@broad_cat Unfortunately, I think he said "Devin, from Legal Eagle is really a lawyer". I can't imagine such an intelligent man as Grady has actually watched many of his videos, else he'd have realized that he is indeed a liar, and not a lawyer. I don't care which side of the aisle you're on, you simply cannot call that man an expert in anything other than opinion.

[@broad_cat]

​@@C4uSt1CO Too true. That's also why such an intelligent person like yourself also hasn't watched many of Legal Eagle's videos, and why it would probably be wise not to comment on their professionalism given your lack of experience with their work. I'm glad that we both being intelligent beings have avoided the scourge that is Legal Eagle, and likewise wouldn't have the gall to comment on their abilities or lack thereof. I mean, if we did consume their content, we must clearly be deficient mentally. Regardless of the side of the aisle you're on, obviously.

[@alastairgillis5717]

It would be intersting to know the ratio of tanker fires at bridges and overpasses to all highway tanker fires. Is something drawing these tankers to the structures? Love your videos.

[@doublej1076]

My hunch would be that bridges and overpasses are where the large majority of fires occur. Tight curves on on/off ramps, like on I-95, and sudden obstructions just off the roadway, like support pillars, leave a lot less margin of error than you'd have on a straight road through cornfields.

[@DavidKMartin]

Bridges and overpasses are inherently less forgiving of driver errors or vehicle mechanical failures than many other parts of roads. For instance, the Harrisburg, PA flyover ramp fire (which happened near me) involved an area with a relatively sharp curve for a major road (it's effectively a right- exit "left turn" from an interstate onto a major state highway) and the tanker overturned. The driver took the curve too fast. Without the sharp curve it's less likely the accident would have happened. And even without curves, there's just less margin for error in the form of medians and shoulders.

[@Genius_at_Work]

No, you just don't hear about Fires that aren't under Bridges. I know of similar "Symptoms" myself, as I work on Tanker Ships. These are the most accident-prone Ships in the Public Opnion, while statistics prove the exact Opposite (especiall for Liquefied Gas Tankers). If any other Type of Cargo Ship sinks or burns, nobody bats an Eye as long as there's no Oil Spill involved. But Tankers just have this Public Perception of Oil Spills and disastrous Fires, that they are under constant Scrutiny.

[@jesheezy]

During your description of the discrepancy between the frequency of a failure mode and the resources invested to prevent them, I felt that you glossed over a major factor: Detectability, one of the key parts of the FMEA. I love your ability to explain engineering decision making tools; could you perhaps make a video on the FMEA? Thanks!

[@dalekrohse1871]

This was another high-quality video, Grady. There is a similar situation in the electric utility infrastructure realm. As a retired electrical engineer who worked in the distribution, substation and transmission portions of the industry, we established design and protection/response policies based on the likelihood of a destructive event occurring and the time/cost to recover from it. For example, Over 90% of storms have destructive winds with speeds of 80 mph or less (broad generalization). The engineering divisions or policy makers establish strength standards to withstand 80 mph winds (plus some safety factors). It is known that usually no more than a half mile of transmission line will fall down due to the winds hitting a section. The utility will maintain an adequate inventory of poles, conductors and insulators to replace about a mile of line within a few hours to a couple of days after a significant event. Storms beyond that necessitate a broader response, often coming from several states distant. Typically, the electric utility will purchase insurance coverage for its substations and generators but it won't secure insurance for its distribution lines or transmission lines. They self-insure for the cost of events spread across broad areas of service territory, which can sometimes mean thousands of miles of distribution or transmission lines. A key response tool for both the land transportation network and the electric utility network is to have had a cross-section of its operating division personnel participate (periodically) in "what would we do if....?" exercises to identify the range of possible recovery alternatives. HILP - "High Impact Low Probability" events demand some attention - at least to have been thought about if not also going so far as to acquire a stockpile of fast-response supplies. Keep up your good work!

[@WebberAerialImaging]

But I've been told burning fuel can't damage steel structures...🤨😅

[@OPiguy35]

Would you considering doing an off-grid / backcountry practical engineering series?

[@kentslocum]

I appreciate your point that a reduction in road capacity may encourage people to find alternative modes of transportation, or reduce the frequency of their drives.

[@evanchapman9395]

Excited to see a nod to urban planning channels. Us Americans need more of that content. Thank you!

[@brussels13207]

Another excellent video, explaining all the trade offs to the situation. Keep them coming.

[@eliseleonard3477]

@Practical Engineering Grady, thanks for the fantastic educational content. Would you consider a video about extreme heat events and problems with commercial flight? We’ve had cancellations due to heat here in Phoenix at temps over 120F (most recently 2017) and those temps will be more frequent and persistent in coming years. Do runways have to get longer? Or jet engines souped up to accelerate faster in takeoff? This is a climate change effect that we should probably talk more about.

[@daleinaz1]

Mostly, cargo and passenger loads have to go down. High temps reduce the lift over the wing (because the air under the wing is less dense, same reason hot air balloons don't fly in Phoenix in the summertime). Back in 2017, the tables that told them how much load the plane could carry versus temperature, only went up to 120F. So when it hit 122, they had no official guidance, so they stopped takeoffs. Now the tables go up to (I think) 145F.

[@kenbrown2808]

the final analysis is to compare the cost of an occasional bridge failure due to fire, and the cost of trying to make every bridge fireproof. - and the fact of the matter is that to fireproof most bridges would require them being removed and replaced with much heavier structures, with aggressive fire suppression systems installed in them.

[@20chocsaday]

The Kersh rail bridge might have been built that way because it is still there.

[@timmccarthy9917]

Thank you for addressing induced demand! Too many state DOTs don't.

[@Jalo1138]

The craziness of accelerated construction reminds me of what happened around Pittsburgh a few years ago when US route 30 collapsed near Forest Hills (just east of Pittsburgh). We all expected it to be at least a year before that reopened - it was done in around 3 months.

[@straight_to_finish]

Good, Fast, and Cheap. You clearly made the point that Good & Fast won’t come cheap. Many people don’t understand this concept and expect projects to be completed overnight.

[@emp0rizzle]

Jet fuel can't melt steel beams....

[@beingknox2544]

It can collapse a building (and you know what I mean RIP to all that died and those who survived. I don’t mean to be rude or mean)

[@jackieow]

Anybody every try putting a sprinkler system under a bridge so its water flow could carry away some percentage of the heat?

[@hayleyxyz]

I imagine piping in water would make it not cost effective. A lot of bridges are along highways, far away from water infrastructure. It also probably wouldn't be reliable - normal indoor sprinkers are delicate (they rely on a small glass vial breaking under heat) and I don't think anything exists currently that would be suitable.

[@paisleyprince5280]

Freezing temps 6 months out of the year etc

[@jackieow]

@@paisleyprince5280 Not a problem. The water only comes to the equivalent of a fire hydrant, so it stays underground where it doesn't freeze. The valve opens only once heat sensors send the signal to open the solenoid valve.

[@jackieow]

@@hayleyxyz No more involved than running water to a fire hydrant. A lot of highway bridges are near water, so the water is often right there. This would not rely on small glass vials breaking. It would be (1) heat sensor detects heat and send electric signal down wire (2a) solenoid valve opens underground and allows flow through fire hydrant analogue to spray under bridge, or (2b) pump turns on and pumps from local stream to spray under bridge.

[@SoliseLeili]

This is so interesting. The cinematography and editing is well made. By the way cool glasses!

[@fastfiddler1625]

I feel like we need to address the elephant in the room: the obvious conspiracy of tanker trucks against roadway bridges.

[@nobodynoone2500]

Sounds like electric cars are going to make this trend way WA Y worse.

[@ironnwizzard]

This is really a stealth PSA for fuel pipelines over tanker trucks. Great work Grady!

[@yo9758]

The economics of building pipelines to every gas station would never make sense

[@gregkrekelberg4632]

Excellent video. And Grady, I finally signed up to Nebula. Between you and Sam, I couldn't take it anymore. 😃

[@herzogsbuick]

Rob's video was excellent, I'm glad you brought it up, Grady!

[@rickyh2896]

I grew up right by one of your B roll bridge shots! Had a total double take and had to rewind because I recognized the intersection! Great video as always!

[@No-Me3]

2:45 I was a delivery driver in the Harrisburg area the day that happened. US-22, US-322, and I-81 were all shut down, as well as one of the main thoroughfares into Harrisburg itself. Parts of 81 were damaged below, the bridge for the exit ramp to 322/22 off of north 81 that the tanker turned over on was destroyed, and large sections of the bridge above from another ramp melted away and collapsed. We had to cancel several deliveries that day because traffic was backed up so far all over the place. It literally shut the state government down early that day when the governor sent home state workers in shifts to help with the traffic problems. There was also simultaneously a crash and fire on a section of the PA-Turnpike on the opposite side of the city in a construction zone. What a crazy day that was.

[@Patiboke]

Great that you think about reverb in videos, Grady! 👍 Not everybody does and it makes some videos hard to enjoy.

[@Koger4]

15:20 I like the part where he calls legal eagle a liar

[@miketaggart3803]

In early, early 1980’s a bridge in Pittsburgh caught fire when a steel mill burned and it was closed for a year. Our school bus crossed that bridge all the time and we had to detour to the next bridge. One could see the slight sag it had .

[@Tetracarbon]

The timing of this video’s release coinciding with the second Kirch bridge collapse event is just 👌

[@HelloKittyFanMan]

Haha, Grady, I love your juxtaposition of your phrase "road construction often seems slow" with a video of a guy _on_ a road holding that "SLOW" sign!

[@codybeasenburg6275]

As a Charleston, it made me so unbelievably happy to see one of our bridges at 8:25 💕💕 thank you for this!

[@postpwned3]

Grew up around here,Super excited to see you cover this.

[@Arcexey]

great video as always friend. thank you very much.

[@cjespers]

Thanks for another interesting video, Grady. Well done.

[@fogogin]

I drive over this 5 days a week, the traffic wasn't terrible, you have 295 in NJ and rt1 in PA. The south bound detour was not bad of a slowdown, they had you get off at the exit, a right and a left and you were back on 95. And when they said what they were using for the fill, I knew exactly what they were talking about because I heard it here!

[@TheRoyFoley]

Practical Engineering and Veritasium video in one day? An engineers dream

[@JamesSigarette]

I cleaned the storm drain under this bridge. It was an incredible amount of crushed bridge. There were many manhole covers that were relocated. It was very impressive.

[@mannysantics1833]

15:22 "Devin from Legal Eagle is really a Liar"🤣🤣🤣🤣 I had to replay it a few times to make sure I heard it right.

[@basilman121]

I had the pleasure of joining the Geotechnical firm that produced the retaining wall design and watched a presentation on the design process. You were correct on the loading conditions: an embankment constructed of typical soil would have caused damage to the utilities underneath. The lightweight aggregate reduced the weight that the DOT was okay with.