[bluGill]

There are a number of bridges where I live that cannot handle a truck with trailer. They have large signs warning what the maximum load is.

They are mostly on rarely used roads in farm country (as in a handful of cars per week cross), so a truck with lime is one of the more likely potential loads, but of course the local farmers know that bridge can't handle the weight of a truck and plan their deliveries to take a different route (which often more than doubles the trip time vs if the bridge could handle the weight)

[bombcar]

The problem comes when those type of bridges don't collapse the first time someone overloads them; then people start using it because "eh it works" and eventually it fails.

[pmontra]

Is there some well established way to make some very visible but not structural part of a bridge to collapse after an overload, to scare people and make them report the problem?

[bombcar]

You probably could, but the amount of engineering and cost required would be simpler to just replace the bridge with a stronger one.

Often these "car only" country bridges are just some large wooden beams over a creek; even a simple concrete culvert replacement would be truck-proof.

Some of them do things like this: https://www.alamy.com/stock-photo-small-car-suv-crossing-the...

[yonaguska]

A really simple catch all, that isn't quite accurate for all cases would be to put a sign over the top of such a bridge,that limits the height of vehicles crossing, excluding trucks with the tall trailers. Would not work for loads that aren't tall though.

[mannykannot]

I would have thought a few strain gauges, maybe some logic to filter false positives (if that's a risk) and a light would do a reasonable job.

[bombcar]

Wait until you see the known issues and reports on bridges in the US that did collapse. Nobody monitors this stuff even on important ones.

[rob74]

Here that doesn't seem to be the case. If you look at the western approach to the bridge in StreetView (which is from 2019, the eastern part has imagery after the collapse), there is no weight limitation sign to be seen. As such, you would expect the bridge to be able to carry the load in the worst case scenario of both lanes being filled to capacity with heavy vehicles, so failing because of one single truck and one or two cars is really bad...

[bell-cot]

Reaction: +1...but there is still an "on any public road or bridge" weight limit for trucks, buried somewhere in Norway's regulations for trucking & highways.

The stereotype would be that the law-abiding Norwegian truckers are always careful to keep their trucks below the legal weight limits...but stereotypes aren't always true.

[beAbU]

This Norwegian bridge is practically brand new.

Are these bridges you are referring to from your area really old and poorly maintained bridges?

[bluGill]

Mostly, some date back to the 1800s. Some are a bit more modern, but still mid 1900s. Though in farm country it isn't unheard of to save money buy not building one up to the weight of a loaded truck. For that matter, there are farmers who run more than max weight of the road (this is sometimes even legal, it damages the roads, but replacing a road a bit early is considered cheaper than building to higher capacity - bridge weight limits cannot legally be exceeded though, and farmer going overweight know where they can't go)