The Canopener Bridge | Hacker News Reader

The Canopener Bridge

11foot8.com

81 pointsdjoldman47 comments

The Sydney Harbor Tunnel had this problem. After an over-height truck got wedged in the tunnel and took three weeks to remove, the tunnel operators had to do something drastic. They already had multiple sets of detectors, flashing lights, signs, and movable bars hanging down to bang on overheight trucks. That wasn't enough.

So they had something custom built, which is now a product called Softstop.[1] When the detectors sense an over-height truck, water jets shoot downward across the road. Then, a very high powered projector projects a giant STOP sign on the water curtain, right in front of the truck. That seems to successfully get truckers attention.

Softstop is a complex installation, with pumps, tanks, drains, lights, and controls. It's probably overkill for some minor underpass.

[1] https://vimeo.com/253900884

That’s incredibly cool. I wonder if it could be simplified with misters instead of pouring water, which would at least require less water storage, emitters, and drainage.

Misters probably aren't fast enough, plus the mist would get blown about by air currents, so it wouldn't make a good projection surface...

In case anyone else was curious to see Roland music equipment in that video, it's an AR-3000 Digital Announcement Recorder.

https://www.roland.com/uk/products/ar-3000/

How is such a system cheaper than a big breakable but solid STOP sign on an arm, like those american school buses.

The video explicitly mentions -- "you can't put things in front of vehicles doing 60 or 80kph" (~40-50mph), I assume with the implicated "without causing damage to them or making road conditions unsafe".

Another reason mentioned is that police and emergency response vehicles need to get through.

Other countries do not use this excuse, which actually is irrational.

If a resistant barrier is put before the tunnel at the height limit, it will damage any too high vehicle that attempts to pass, but removing the barrier guarantees that the vehicle will be damaged later, in worse conditions, inside the tunnel.

If the vehicle stops later inside the tunnel, instead of being blocked before it in some place with good visibility, then the road conditions will certainly be even unsafer.

It's a question of liability at that point, not damage to the vehicle. If I put a barrier across the road, and you hit it, you can make the argument that while you hit the barrier you wouldn't have hit the tunnel roof. That's going to play out differently in different jurisdictions, I'm sure.

I imagine like many things in the US - it's about liability. Putting in a barrier specifically designed to damage your vehicle could be seen as accepting liability for it(even though it prevents larger damage if you continue). A bridge damaging your vehicle isn't there on purpose - it's your own fault for ignoring it.

Other countries aren't as litigious as the US so I suspect it's just easier to do things like that.

Considering this was installed at a tunnel in Australia, I don’t think how liability works in the US is relevant. Plus, these steel bars are pretty standard in the US, albeit they are installed in locations where large vehicles are not going at high speeds.

The litigiousness of the US is a myth.

Or a barrier that will do a lot of damage to the truck and stop it but be easy to remove when you need to unwedge the truck and pull it out? You could make something like this out of cheap steal and paint it brightly then bolt it to the higher roof ahead of the actual low roof.

In the video they explained that part of their reasoning with the water curtain is that this solution allows ambulances and police to drive through the stop sign without damaging their vehicles or slowing them down or removing the sign.

Other countries use a much cheaper method.

At some distance before the tunnel or passage under a bridge with limited height (but after the signs that advertise this) there is a solid metal barrier at the height limit and when any too high truck attempts to go forward (which of course happens from time to time) the barrier cuts the top of the truck, which is guaranteed to attract the attention of the drivers (and presumably the anger of their employer).

EDIT: I have posted this before watching the video, which shows exactly how this method, of using a steel "crash beam" works.

In this case, the truck was only slightly above the height limit, but in another place I have seen a similar incident where the truck was higher so all its roof has been cleanly cut and detached from the truck.

This is the right method of handling such height limits, the only one that is guaranteed to be foolproof.

Even if it damages the vehicle, if the vehicle were able to pass with an extra height, it is certain that it would be damaged anyway, but in worse conditions, especially in the case of a tunnel.

Near where I live we've got a guided busway (a track system that modified buses can travel down, tram-style).

On the railway bridge before it's entrance there's a height barrier in advance consisting of a whole load of bells that dangle down from a metal bar and will hit over-height vehicles without making a really solid collision.

They still haven't figured out a way to stop cars driving up the bus tracks, though (where they inevitably get stuck).

> This is the right method of handling such height limits, the only one that is guaranteed to be foolproof.

Near where I grew up, there was a low bridge. At one point many years ago, an excavator on a low-loader hit the bridge, causing the excavator arm to swing around... into the upper deck of a loaded bus travelling in the opposite direction.

The point is, this method might be foolproof in terms of preventing damage to the bridge, but it has other potential drawbacks.

> I have posted this before watching the video

They've done every conceivable thing to mitigate the problem at this bridge. Watch the old videos, before they had the crash bars and huge signs and flashing lights. Before they raised the bridge to the limit of what the rail line could tolerate.

> This is the right method of handling such height limits, the only one that is guaranteed to be foolproof.

Well, it probably causes a lot more risk to life than the water curtain one.

To be fair, it's the driver that's causing the risk to life, not the barrier.

It makes sense to provide plenty of warnings and if a driver isn't paying attention, then they need to be stopped before they damage something really expensive.

What is the industry standard threshold of expensive damage where an engineer can decide to kill a person to avoid it? I imagine this comes up often enough there would be some sort of formal guidance about it.

My perhaps naive understanding of civil engineering professional ethics is that this decision is off limits to them. They may design a system to fail in ways that are less harmful to life than others, but not to cause human harm or death when it could otherwise be avoided.

In any case, if you do design such a system, the driver may be at proximate fault but it's hard to say it's entirely on them.

Most objects aren't designed to withstand impacts from heavy machinery (e.g. lorries) without endangering anyone and it's not normally considered. Shop windows can cause significant damage to people if a vehicle is driven into them, but it's not really anything to do with the ethics of window designers/manufacturers/installers.

If there was a large pointy protrusion that was designed to cause harm, then you would have a stronger point(!) that it was designed to be dangerous.

Merely having a height barrier before the very similar height barrier of the tunnel itself is hardly making anything more dangerous and I'd consider it less likely to cause harm to life as emergency responders can get better access to the people involved rather than possibly having to dig them out of a tunnel first.

Also, a height barrier is unlikely to cause major physical harm to the driver, so I think you've over-egged your position.

Right but once you've decided to intervene to stop the driver from damaging the bridge, the mechanism of stoppage is your responsibility. The way you stop them may not be, and doesn't have to be, safer than what would happen without intervention. But at the same time you can't go "eh it's cheaper just to kill them."

Hitting the height barrier is likely to be less harmful to the driver and other people than hitting the bridge itself, so that seems to be taking due care (and again, killing the driver is extremely unlikely in either scenario).

The purpose of a height barrier is to act as a sacrificial component and I would consider that it improves the safety of the structure as well as being cheaper. It's a very common design to see metal or concrete poles (bollards) used to prevent drivers from causing harm to other road users, features or shop fronts. They're safe and effective.

Yeah, or just some metal pipes on a string; if the vehicle hits it, it'll cause a racket but no significant damage.

Those were already there, the trucks ignored them...

The Tunnel de l'Étoile[1] use to have the same problem until it was closed in 2015. It's now reopened as a bicycle only tunnel.

It had blog associated with it; now defunct and cybersquatted but you can still see what it looks like through the wayback machine [2]. It was one of the earliest novelty blog I remember.

[1] https://en.m.wikipedia.org/wiki/Tunnel_de_l%27%C3%89toile

[2] https://web.archive.org/web/20230000000000*/http://www.2m40....

We got a similar issue in Boston - the Storrow bridge. So much so we call it "getting Storrowed"[0]

[0] https://www.boston.com/news/local-news/2021/08/19/boston-sto...

The wonderful thing about Storrow Drive—it’s a MAJOR ARTERY that is integral to traffic flow in downtown Boston. Since Boston has so many students, September 1st is like an informal holiday[^1] where we wait for newcomers to Storrow their U-Hauls.

[^1]: actually one of two September 1 holidays observed. The other is “Allston Christmas,” when the streets of a popular student neighborhood are filled with free furniture people tossed out when they moved.

Fun fact! The namesake of Storrow Drive was "an investment banker who led a campaign to create the Charles River Basin and preserve and improve the riverbanks as a public park. He had never advocated a parkway beside the river, and Helen Storrow, his widow, publicly opposed it"

It's one of the urban highways that can absolutely go, and should.

In Europe, E-routes require a clear height of 4 metres, which is the maximum allowance for a regular vehicle. So if you're a trucker, you can be safe in knowing that driving on an E-route, means your vehicle will clear all bridges.

There are definitely examples of countries upgrading their existing roads to become E-routes, which sometimes include raising bridges.

11 Foot 8 – The Can-opener Bridge - https://news.ycombinator.com/item?id=23587190 - June 2020 (202 comments)

The Montague St Bridge (affectionately known as Monty) similarly likes to turn box trucks into parallelograms:

https://howmanydayssincemontaguestreetbridgehasbeenhit.com/

Monty is 3.0m (9ft 10in).

I used to watch this on YouTube regularly until right about when the city tried to make the underpass deeper.

It didn't help, hah.

Sadly making the underpass deeper did help a little bit. There are now a lot less videos than there was in its heyday (it's 12'4" now, which is a pretty normal bridge height).

Also, I think they raised the railroad rather than lowering the road. I believe there is a video of the weekend they did it on the channel.

I live in Durham and drive by this occasionally, but funny enough I don’t think I’ve ever needed to drive under it. They actually raised it a few years ago, but it still claims the occasional truck.

There's some similar fun to be found by following the World Bollard Assocation on the platform formerly known as Twitter

https://www.thepoke.co.uk/2023/01/06/the-world-bollard-assoc...

A bridge like this would make a great plot point in a big-dumb-action-style heist movie. Force a truck under a low canopener bridge at speed to rip its top off, then herd it onto the highway to drop people in via helicopter and extract the package.

This happens in the first big chase scene in the beginning of Terminator 2.

Used to work in an office overlooking this bridge. When a crash happened all work ceased and we’d gather around a window to gawk at the accident. Sometimes it felt like they came in clusters.

I felt extra bad when it was a rental.

Interestingly random events like this do tend to cluster. There are lots of arrangements where clusters exist and very few where it doesn't, so clustering is a lower entropy state. Plane crashes are similar.

https://en.m.wikipedia.org/wiki/Poisson_clumping

https://stats.stackexchange.com/questions/109390/how-odd-is-...

There are a few bridges like this in Saigon on Truong Sa / Hoang Sa streets that run along a long river through the city. They are super busy traffic streets at almost all times of the day.

It was always entertaining to watch trucks get stuck under them almost daily and back up traffic on the little streets for hours.

Found a google maps photo of one of the bridges... https://goo.gl/maps/8eFk6EgxbdvhMyNk8

Looks much more like a thickness planer than a can opener to me.

Yo, does that go any lower? I need another quarter inch off that truck.

Here's a website set up to track crashes involving another infamous bridge in Perth, Australia: https://www.howmanydayssincebayswaterbridgehasbeenhit.com/

happens with much older structures: https://romanlincolnshire.wordpress.com/2017/05/18/a-close-s...

the most smh aspect of this was that truck actually does fit under that bridge, it just doesn't fit under the even lower warning board.

the whole thing was an accident intending to happen!

It's not a warning board. It's a crash beam to protect the bridge, because the consequences of damaging the rail bridge are much worse than those of canopening a truck that ignored numerous obvious warnings, including a flashing one triggered by a vehicle height sensor. The bridge itself has already been raised by 8 inches (though it's still unusually low), which would have also cost a fair bit. They haven't just gone and put an unnecessary "warning board" under it.

There are many more incidents, BTW. Scroll down for more videos.

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