The bridge projects I've been on spec 75 or 100 years. Main difference is better protection/sacrificial depth on ferrous members.
The average age of a bridge in the USA is 43 years. But we also have an epidemic of unmaintained bridges.
No bridge made today is designed to last indefinitely. Many different forces will degrade the bridge over time, even with maintenance. Steel stresses weaken it over time. Concrete weathers over time due to salt, chemicals, water, wind, and the steel reinforcements tend to corrode eventually.
Stone bridges may last for an exceptionally long time, but their weight and expense makes them only useful in limited applications, typically as small rail overpasses. Ones that were designed for horse and buggy end up slowly failing as heavier trucks and cars in traffic weaken them.
The same fate lies for timber bridges. When well maintained they can last for 75 years, but it's expensive and requires certain skills. They were also mostly designed before heavier cars and trucks, and for less traffic. Most famous covered bridges today are being closed to traffic due to increased wear.
FHWA provides up to $7 Billion in assistance in maintaining bridges. But it would take at least $125 Billion to begin dealing with the structurally deficient bridges in the USA, according to the ASCE Infrastructure Report Card[1].
Add to this the fact that many bridges in the US are privately owned, and it's the responsibility of the bridge owner to maintain them. But guess what's not profitable for a private enterprise? Maintaining bridges. Despite this, train derailments and property damage continue every year due to unmaintained bridge and train infrastructure.
The executive has proposed funding for repairs, but as usual, it's not enough[2]. So far they've gotten almost half that number of bridges repaired, and pledged another $300M,[3] which is still just a drop in the bucket of what's needed of the backlog; it doesn't address all the new maintenance that will be needed each year.
According to the American Road & Transportation Builders Association, there are 167 million crossings on 42,400 bridges rated in poor condition. [4]
[1] https://infrastructurereportcard.org/cat-item/bridges-infras... [2] https://www.nbcnews.com/news/us-news/biden-has-plan-fix-amer... [3] https://www.whitehouse.gov/briefing-room/statements-releases... [4] https://artbabridgereport.org/congressional/map
Is it impossible for these things to stop happening? No, not at all. But it's probably not going to stop, in this country, because we let private industry get away with whatever they want. If this were the UK the story would be very different.
I mainly made that comment because it still blows my mind the the City Bridge Foundation has been going for 740 years
Though to be clear designed to last 50 years isn't the same as saying it will only last exactly 50 years, or that theirs nothing you can do to extend a bridges lifespan if it's replacement is running a little late.
The bridges we can all name are pushing 100+ right?
They more or less do continuous maintenance during the warmer months of the year.
(So older than 50, but younger than 100)
https://en.wikipedia.org/wiki/Zilwaukee_Bridge
Sticking with the mid-western therme, the Chicago Skyway was built in 1958
I’d argue the Bayonne Bridge raising kinda counts since it was almost a rebuild and more impressive in many ways since it stayed open the whole time.
Meanwhile in the San Francisco Bay Area they replaced the Bay Bridge…
1. Built to last only 50 years to save on materials (as the other commenter noted).
2. Built over literally the widest possible part of the Hudson because the governor got in a pissing contest with the Port Authority and wanted all the tolls to go to the state, which wouldn't have been the case had it been built like 2 miles south where the river is narrower.
3. Designed with zero redundancy, such that a "critical fracture could make the bridge fail completely because its supports couldn’t transfer the structure’s load to other supports." [0]
So yeah if we're being real, 50 years was quite optimistic.
The new Tappan Zee is apparently supposed to last 100 years, though given the incidents with substandard materials being used, as well as ever-increasing traffic, who knows.
That said, driving over a bridge 10 years past its planned EOL and being able to look down directly to the water through gaps in the concrete was always a nice feature though -- who needs coffee when you've got that to get your heart rate up!
[0]: https://en.wikipedia.org/wiki/Tappan_Zee_Bridge_(1955%E2%80%...
Keeping in mind that mid-century Japan and Germany were in ruins and the possibility of nuclear annihilation of urban centers very much at the top of many people minds. 50 years may have seemed an optimistic survival rate of built structures at the time.
https://www.nytimes.com/2006/01/17/nyregion/a-bridge-that-ha...
Its replacement is a self-anchored suspension bridge.
The original western span, actually a double suspension bridge, remains standing, as constructed in 1933, 91 years ago.
Here's an interesting list of major bridges with dates, most of the newer ones being replacements: https://www.carolinadesigns.com/obx-guide/fun-info/bridges/
They even note a rare exception designed to last 100 years with maintenance.
The Millau Viaduct also comes to mind when thinking of famous, iconic modern bridges.
There are now two Tacoma Narrows Bridges. The oldest was built in 1950. The one that infamously collapsed was built in 1940. The newer bridge is from 2007. The West Seattle Bridge was closed due to damage in 2020 and reopened after repairs in 2022. It was originally built in the 1980’s after the previous bridge was hit by a ship. There are two floating bridges on I-90 east of Seattle. One of them sunk during reconstruction work in 1990 and was replaced. Theres also a new 520 floating bridge that opened in 2016. The Hood Canal Bridge (also a floating bridge) originally opened in 1961, sunk in 1979, was reopened in the 1980’s, and large parts of it were replaced in the 00’s.
The Ballard Bridge actually is over a century old! It was opened in 1917. However there was a lot of reconstruction done during the 1930’s. The Fremont Bridge is also from 1917. Both of these bridges span a ship canal that was built between 1911 and 1934. The Aurora Bridge was also built in the 1930’s.
In the DC/MD/VA area, almost all the bridges I can name are less than 100 years old. Woodrow Wilson, American Legion, Chesapeake Bay Bridge, Chesapeake Bay Bridge-Tunnel, Key Bridge, Key Bridge, Nice Bridge, Memorial Bridge, Chain Bridge, 14th street bridges... Some of those were even built after 2000! Also the New River Gorge Bridge in WV is pretty famous and not even 50.
Well, actually, the Key Bridge (in DC) apparently turned 100 years old last year. And I guess the Long Bridge (though not a road bridge) is also over 100...
https://en.wikipedia.org/wiki/I-35W_Mississippi_River_bridge
Makes me want to find the data now. I don't actually known if our bridges are too old, poorly maintained and falling apart early, or if the whole topic is just herd mentality and politics.
Fern Hollow Bridge Mk. II?
There's a list of many more failures at Wikpedia, though international in scope:
<https://en.wikipedia.org/wiki/List_of_bridge_failures>
There are a number of ship-bridge collisions listed, as well as fuel-tanker explosions, which seems to be a surprisingly common failure mode.
Also numerous failures in China, though how much of that is simply a scale effect I can't say.
So it's an issue, but those bridges where also constructed by a far poorer nation so it's not that big a deal.
That's a must more interesting question when discussing the topic of infrastructure.
Sure we've created a lot more money in the last 50 years, but we've also lost a lot of domestic manufacturing. When it comes to something as vital as roads and bridges are we poorer when we have less paper money or when we are less independent in the manufacturing and maintenance of them?
I think people feel poorer because income inequality increased so much. New homes are huge because new home buyers are the upper end of the wealth curve. Same deal with cars etc. Stuff that targets everyone like normal sized TV's ends up being extremely cheap because revealed preferences show people buy cheap when it's an option.
Production per capita may have gone up, but that's (a) likely measuring productivity in financial terms and (b) heavily correlated with an increase in natural resource consumption, especially fossil fuels.
If we want to consider ourselves richer because we are able and willing to use more natural resources today could lead down a dark (and very hot) road.
Compare a modern jet with one from the 1974 and sure many passengers have less leg room but it's hauling both people and 3rd party cargo while still using far less than 1/2 the fuel per passenger mile. Such improvements really add up and include things like engineered lumber using fast growth pines.
Look at the most popular car 50 years ago and you'll see the Ford Pinto. It's slow, unsafe, tiny, time consuming to maintain, fuel inefficient, and missing modern amenities but it was affordable. Inflation adjusted it's roughly the cost of a Mitsubishi Mirage which while better in just about every way is a rough equivalent the reason people are buying crossovers rather than the Mirage today is because people just have more wealth in real terms.
The data I found only goes back to 1965 [1], but from the absolute peak in the 70s to today we've reduced per capita use by around 30%. Over the last 20 years we've reduced it by around 15%, going back 10 years and the reduction is only around 5%. Time scale matters a lot here, as does a definition of what "way downdowm" would mean in real % reductions.
I totally agree we've made use of oil more efficient in things like engine efficiency. We've also found more uses for oil byproducts, which can be good or bad depending on your opinion (and again, on your time scale). If we've improved fuel efficiency by 50% and at best reduced fossil fuel per capita by 30%, we've squandered some of those gains by using more oil for other things.
Whether that's a good or bad thing is really up to opinion, goals one has in mind, and how one weighs the trade offs.
[1] https://ourworldindata.org/grapher/fossil-fuels-per-capita
That chart gives 31% in 49 years 63,836 in 2022 vs 92,635 in 1973, but the numbers are dropping faster each year.
it's not that clear-cut. regulations regarding construction are many times more strict, as well employment restrictions and safety code.
I mean, the things like the transcontinental railroad were built with what would largely be considered inhumanely treated human slaves by today standards -- that kind of 'advantageous hiring condition' thankfully no longer exists.
Stuff like that plus millions of other regulatory nuances that drive the cost of development to be many times more expensive than during the bad old 'wild west' make these kind of value analysis gapped by many years near impossible.
As to regulations, in 2023 an I-95 bridge failed after a gasoline tanker truck fire. They took 12 days to get a temporary replacement that got traffic flowing again. You occasionally see such projects where we need a fix now and then it happens. However, it was a temporary replacement and they needed an actual long term solution.
The difference between such rapid projects and more typical ones include time consuming steps to preventing dirt from settling and causing problems in the future etc. Regulations are filled with such tradeoffs, but that doesn't mean we're unable to move more quickly just that we can afford to do something else.
https://en.wikipedia.org/wiki/The_Iron_Bridge
Opened in 1781, still in service and perfectly safe. Of course, there are no container ships nearby. But I reckon you could sail a container ship under it, given enough water; and to damage the bridge supports, the container ship would need climbing equipment.
1781 isn't many years after the Declaration of Independence.
But that's talking about the tail end of the bell curve not it's center.
It didn't take motor traffic, because when it was built, there was no motor traffic. But the claim I replied to was about all bridges. But it used to take vehicle traffic: the WP article says "In 1934 it was designated a scheduled monument and closed to vehicular traffic."
A tiny fraction reach 500 and so far none that we know of have hit 5,000 though there’s a few possibilities.
For example, if tomorrow we decided to build a new bridge next to every old bridge, average lifespan would half.
> if tomorrow we decided to build a new bridge next to every old bridge, average lifespan would half.
The only way building a bunch of new bridges changes lifespan is if we changed how they where built.
Figuring out lifespan rather than age is at best an approximation after looking at the bridges that didn't survive and the condition of bridges that do, but the uncertainty is low.
They are designed to withstand smaller boat impacts because they occur relatively frequently, but cost vs benefit on rare events that are difficult to mitigate is quite different.