7 ms·

New Analysis Confirms Why the Skagit River Bridge Collapsed

61 points by curtis 10y ago

fnj 10y ago
"The driver was following the pilot car too closely: more than half the recommended distance for adequate response (400 feet, or a five-second response time, instead of the recommended 865 feet, allowing for a 10-second response time)." Er, that's less than half the recommended distance. How did the copy editor let that through?
- sverige 10y ago
  The braking distance increases with velocity. The measurement is in seconds, not feet.
  - mikeash 10y ago
    Following time and following distance are linearly related. Either way, it's less than half.
    - sverige 10y ago
      Braking distance is not linearly related to following distance. Braking distance is what is being referred to here.
      - mikeash 10y ago
        They're pretty clearly talking about following distance there.
sintaxi 10y ago
> The authors recommend changing policy to report the lowest vertical clearance for bridges, rather than the highest Common fucking sense.
- foota 10y ago
  I mean, you do want trucks that are able to go over a bridge to be able to go over it.
  - yuhong 10y ago
    I don't think it is particularly good design anyway.
    - mjevans 10y ago
      It's a good design for 99% of the time and a very good design from a high speed traffic flow point of view. It requires minimal ramp up to crossing a feature that is nearly at the level of surrounding land. The correct engineering solution is to have diversity of designs, including an 'open top' bridge near by, which can serve the other cases as well as critical backup traffic during the failure. You might note that most of the preventative measures outlined do not modify the design of the bridge, but focus on actually keeping records that track the more critical /minimum/ clearance value, as well as more accurately detecting and reporting to the traveling 'over-sized' vehicle that an abort condition has been reached.
- techsupporter 10y ago
  > Common fucking sense. No, it isn't, and this is one of the problems when the "general public" comments on engineering things. It's not that people aren't capable of understanding; they lack the experience to understand why something is the way it is. Someone on /r/seattle[0], where this was recently posted, put it more politely than I: === It's because that extra two feet can be valuable when carrying oversized loads. Frankly, this all falls on the driver of the oversized vehicle, the driver of the pilot car, and the hauling company. - The driver of the oversize vehicle is responsible for knowing his load height. A hauler I've worked with before has it in their manuals that the driver must personally measure the load if there is any question. That driver must also stay far enough back of the pilot car to stop in case of a problem. - The driver of the pilot car fucked up royally by missing the sound of the height-verification antenna hitting the bridge. That is a massive error that should see that pilot car driver drummed out of the industry. - The hauling company erred drastically by not pre-running the route, or at least the low clearance segments, to verify where the clearance exists. That is "oversize hauling 101." The article says the state "rubber stamped" an oversize permit. No, they didn't. The hauler certified that the hauler had pre-run the route. It is required that the hauler state that the route has been verified when the permit is issued. "It is the responsibility of the permit applicant to check, or prerun, the proposed route and provide for safe maneuvers around the obstruction or detours as necessary." - WSDOT bridge clearance tool (http://www.wsdot.wa.gov/data/tools/bridgeclearance/ http://www.wsdot.wa.gov/data/tools/bridgeclearance/) 0 - https://www.reddit.com/r/Seattle/comments/50167q/new_analysis_of_the_2013_skagit_river_bridge/ https://www.reddit.com/r/Seattle/comments/50167q/new_analysi...
mannykannot 10y ago
There is no mention of installing a sturdy beam across the road slightly lower than the least clearance, just a suggestion that the least clearance should be reported, and an extended discussion of the multiple (and rather unsurprising, IMHO) ways in which the pilot car system failed. I am reminded of the half-assed measures that were taken to mitigate the risk of DC10 cargo doors blowing open, prior to the Turkish Airlines crash in Paris. Am I missing something here?
- maxerickson 10y ago
  It isn't really that terrible an idea for the owner of the bridge to allow vehicles across that will only fit in the center lanes. They just need to make sure that the drivers understand that the height limit is lower in the outer lanes.
  - revelation 10y ago
    make sure that the drivers understand Yeah, right. https://www.youtube.com/c/yovo68 https://www.youtube.com/c/yovo68
    - ars 10y ago
      That sign is horrible! It's like it was designed to be utterly useless. "Overheight must turn" means to virtually all "IF you are Overheight you must turn". Obviously that driver doesn't think he is overheight. Change it to "Warning: Overheight truck detected in this lane" (with proper lights/arrows pointing to lane). And blink red as well.
      - vt240 10y ago
        I wonder if they focus grouped the signage ? To me it seemed clear, but now that you point it out... I see where the confusion could happen!
        ars 10y ago
hga 10y ago
This is the first I've heard that the I-35W Mississippi River bridge in Minneapolis was "fracture critical", and even if it was, the design flaw of too small gusset plates would possibly make that moot when one of them gave way, since others that were too small would then fail more easily.
6nf 10y ago
The sheer number of things that had to go wrong for this disaster to happen is impressive.
- khuey 10y ago
  Indeed. The system works, most of the time.
PhantomGremlin 10y ago
I haven't seen this image posted recently. It's wonderful: https://www.reddit.com/r/funny/comments/4ehaka/on_the_road_to_success_there_are_no_shortcuts/ https://www.reddit.com/r/funny/comments/4ehaka/on_the_road_t... ON THE ROAD TO SUCCESS, THERE ARE NO SHORTCUTS.
13of40 10y ago
"that doesn’t account for the economic losses that the area felt because they and visitors no longer had access to the interstate" I've got a pretty awesome picture of me and my son standing in front of that empty section of bridge from the detour route. They essentially routed I-5 traffic into the town and across another bridge. If I had to guess, the stores in that area probably made more money during the detour...

61 points by curtis 10y ago

fnj 10y ago

"The driver was following the pilot car too closely: more than half the recommended distance for adequate response (400 feet, or a five-second response time, instead of the recommended 865 feet, allowing for a 10-second response time)." Er, that's less than half the recommended distance. How did the copy editor let that through?

sverige 10y ago
The braking distance increases with velocity. The measurement is in seconds, not feet.
- mikeash 10y ago
  Following time and following distance are linearly related. Either way, it's less than half.
  - sverige 10y ago
    Braking distance is not linearly related to following distance. Braking distance is what is being referred to here.
    - mikeash 10y ago
      They're pretty clearly talking about following distance there.

sintaxi 10y ago

> The authors recommend changing policy to report the lowest vertical clearance for bridges, rather than the highest Common fucking sense.

foota 10y ago
I mean, you do want trucks that are able to go over a bridge to be able to go over it.
- yuhong 10y ago
  I don't think it is particularly good design anyway.
  - mjevans 10y ago
    It's a good design for 99% of the time and a very good design from a high speed traffic flow point of view. It requires minimal ramp up to crossing a feature that is nearly at the level of surrounding land. The correct engineering solution is to have diversity of designs, including an 'open top' bridge near by, which can serve the other cases as well as critical backup traffic during the failure. You might note that most of the preventative measures outlined do not modify the design of the bridge, but focus on actually keeping records that track the more critical /minimum/ clearance value, as well as more accurately detecting and reporting to the traveling 'over-sized' vehicle that an abort condition has been reached.
techsupporter 10y ago
> Common fucking sense. No, it isn't, and this is one of the problems when the "general public" comments on engineering things. It's not that people aren't capable of understanding; they lack the experience to understand why something is the way it is. Someone on /r/seattle[0], where this was recently posted, put it more politely than I: === It's because that extra two feet can be valuable when carrying oversized loads. Frankly, this all falls on the driver of the oversized vehicle, the driver of the pilot car, and the hauling company. - The driver of the oversize vehicle is responsible for knowing his load height. A hauler I've worked with before has it in their manuals that the driver must personally measure the load if there is any question. That driver must also stay far enough back of the pilot car to stop in case of a problem. - The driver of the pilot car fucked up royally by missing the sound of the height-verification antenna hitting the bridge. That is a massive error that should see that pilot car driver drummed out of the industry. - The hauling company erred drastically by not pre-running the route, or at least the low clearance segments, to verify where the clearance exists. That is "oversize hauling 101." The article says the state "rubber stamped" an oversize permit. No, they didn't. The hauler certified that the hauler had pre-run the route. It is required that the hauler state that the route has been verified when the permit is issued. "It is the responsibility of the permit applicant to check, or prerun, the proposed route and provide for safe maneuvers around the obstruction or detours as necessary." - WSDOT bridge clearance tool (http://www.wsdot.wa.gov/data/tools/bridgeclearance/ http://www.wsdot.wa.gov/data/tools/bridgeclearance/) 0 - https://www.reddit.com/r/Seattle/comments/50167q/new_analysis_of_the_2013_skagit_river_bridge/ https://www.reddit.com/r/Seattle/comments/50167q/new_analysi...

mannykannot 10y ago

There is no mention of installing a sturdy beam across the road slightly lower than the least clearance, just a suggestion that the least clearance should be reported, and an extended discussion of the multiple (and rather unsurprising, IMHO) ways in which the pilot car system failed. I am reminded of the half-assed measures that were taken to mitigate the risk of DC10 cargo doors blowing open, prior to the Turkish Airlines crash in Paris. Am I missing something here?

maxerickson 10y ago
It isn't really that terrible an idea for the owner of the bridge to allow vehicles across that will only fit in the center lanes. They just need to make sure that the drivers understand that the height limit is lower in the outer lanes.
- revelation 10y ago
  make sure that the drivers understand Yeah, right. https://www.youtube.com/c/yovo68 https://www.youtube.com/c/yovo68
  - ars 10y ago
    That sign is horrible! It's like it was designed to be utterly useless. "Overheight must turn" means to virtually all "IF you are Overheight you must turn". Obviously that driver doesn't think he is overheight. Change it to "Warning: Overheight truck detected in this lane" (with proper lights/arrows pointing to lane). And blink red as well.
    - vt240 10y ago
      I wonder if they focus grouped the signage ? To me it seemed clear, but now that you point it out... I see where the confusion could happen!
      - ars 10y ago

hga 10y ago

This is the first I've heard that the I-35W Mississippi River bridge in Minneapolis was "fracture critical", and even if it was, the design flaw of too small gusset plates would possibly make that moot when one of them gave way, since others that were too small would then fail more easily.

6nf 10y ago

The sheer number of things that had to go wrong for this disaster to happen is impressive.

khuey 10y ago
Indeed. The system works, most of the time.

PhantomGremlin 10y ago

I haven't seen this image posted recently. It's wonderful: https://www.reddit.com/r/funny/comments/4ehaka/on_the_road_to_success_there_are_no_shortcuts/ https://www.reddit.com/r/funny/comments/4ehaka/on_the_road_t... ON THE ROAD TO SUCCESS, THERE ARE NO SHORTCUTS.

13of40 10y ago

"that doesn’t account for the economic losses that the area felt because they and visitors no longer had access to the interstate" I've got a pretty awesome picture of me and my son standing in front of that empty section of bridge from the detour route. They essentially routed I-5 traffic into the town and across another bridge. If I had to guess, the stores in that area probably made more money during the detour...