The M20 Footbridge crash

[Gathursty]

From the BBC,
http://www.bbc.co.uk/news/uk-england-kent-37204050

Kent M20 shut after crash and footbridge collapse
A pedestrian footbridge has collapsed on a motorway on one of the busiest travel days of the year.

The M20 in Kent is closed between junctions 3 and 4 because of a "vehicle striking a bridge" on the eastbound carriageway, Highways England said.

Kent Police said the crash was being dealt with as a major incident and one person had been injured.

Travel disruption is said to be severe, with the motorway likely to be closed for some time.

Officers said no-one was believed to be trapped in the debris and the person who had been hurt had injuries that were not life-threatening....

How harrowing for those immediately nearby. Hope everyone affected is okay. I think people in Kent will be seething as the M20 is also clsoed from time to time because of Operation Stack.

 

[theageofthetra]

Looks like something came off the back of a plant truck, hit the following truck whose cab rode up and hit the bridge. Its a thin concrete footbridge which I believe has had a history of being ridden over illegally by quad bikes/trail bikes-though doubt that was cause of structure collapse in this case.

 

[najaB]

Looks like something came off the back of a plant truck, hit the following truck whose cab rode up and hit the bridge. Its a thin concrete footbridge which I believe has had a history of being ridden over illegally by quad bikes/trail bikes-though doubt that was cause of structure collapse in this case.

Agree that the quad bikes aren't likely to be a contributing factor as most foot bridges are a lot stronger than they 'need' to be. I'm relieved that only one person was injured as it had the potential to be a lot worse.

 

[Groningen]

How can a bridge be too low?!

 

[Johnuk123]

How can a bridge be too low?!

The bridge isn't too low but the digger on the lowloader was too high, maybe the arm came loose which is often the case

 

[Mojo]

Was the bridge undergoing repair or something? As photos show temporary fencing on it.

 

[Haydn1971]

That's eased a minor problem we had on the All Lane Running scheme my firm is working on - the bridge necessitated a couple of departures for the proposed slip roads to the west of that bridge - love it when a plan comes together

Thankfully, no one seriously injured !

 

[J-2739]

Glad everyone is fine, hope disruption doesn't last for too long!

 

[telstarbox]

That's eased a minor problem we had on the All Lane Running scheme my firm is working on - the bridge necessitated a couple of departures for the proposed slip roads to the west of that bridge - love it when a plan comes together

Thankfully, no one seriously injured !

Excellent.

 

[richw]

The bridge isn't too low but the digger on the lowloader was too high, maybe the arm came loose which is often the case

The bridge is too low, its clearly a low bridge, but looking on Street view there are no warning signs. I've just followed the motorway on street view from Junction 4 all the way to the offending bridge and there is no signage warning of the low bridge.

The bridge is sloping from one side to the other with much less clearance on the London bound lane compared to the coast bound sign.

https://www.google.co.uk/maps/@51.3...DHJZQ_cn9mgjemIkDg!2e0!7i13312!8i6656!6m1!1e1

 

[IanD]

The bridge is too low, its clearly a low bridge, but looking on Street view there are no warning signs. I've just followed the motorway on street view from Junction 4 all the way to the offending bridge and there is no signage warning of the low bridge.

The bridge is sloping from one side to the other with much less clearance on the London bound lane compared to the coast bound sign.

https://www.google.co.uk/maps/@51.3...DHJZQ_cn9mgjemIkDg!2e0!7i13312!8i6656!6m1!1e1

A bridge only needs a height marker if lower than 16.5 feet.

 

[najaB]

The bridge is too low...

According to reports, the truck that was carrying the loader was driving along the hard shoulder. So the reduced clearance might not normally have been a problem.

 

[richw]

According to reports, the truck that was carrying the loader was driving along the hard shoulder. So the reduced clearance might not normally have been a problem.

A similar style of sloping bridge on either the M5 or A30/A38 has signs on the hardshoulder only. I cant remember where but it was between Bristol and Cornwall - I cant remember which road its on.
Do we know the height of the bridge?

 

[Busaholic]

When I worked for the Probation Service in the 1980s I was told that the serial offender who caused the most grief in the Dartford area of Kent was crossing a footbridge over the A2 aged 4, with his mother, when a crane struck the bridge, bringing it down and killing the mother. His 'offending' started at a very early age and, in that professional's opinion, was directly related to the trauma he suffered. I'd never heard of a footbridge brought down like this before, so for it to happen again in the same county, albeit decades apart, is unfortunate.

 

[tellytype]

Was the bridge undergoing repair or something? As photos show temporary fencing on it.

Been like this for as many years as I can remember

 

[MotCO]

Looking at the photos in the press, I am not convinced that the lorry hit the bridge. Firstly, if the bridge was hit, it must have been the span not the support since the support is too far to the left, yet there is an overhead gantry immediately before which seems to be the same height. If the lorry hit the bridge, it would also surely have hit the gantry.

Secondly, the lorry is pictured as being on the hard shoulder. Why was this? Was it broken down and stationary, in which case it clearly could not have hit the bridge. Or did it veer to the left on to the hard shoulder when it saw the bridge collapsing, so again the lorry did not cause the bridge to collapse.

Lastly, the break in the bridge seems to have a clean cut. If the lorry hit the bridge on the left hand side, then would this have caused an instant collapse of the entire bridge over the westbound carriageway? Also given that there had been some on-going repair work, was this to repair some structural weakness?

 

[fergusjbend]

It is reported that a transporter with two diggers behind was travelling along the west-bound hard shoulder when the arm of one of the diggers struck the bridge support.

Why the truck was on the hard shoulder is not apparent. Nor is it apparent why the bridge should suffer such a catastrophic failure.

Thank goodness the casualty list was limited to one biker with broken ribs. It could have been much worse.

 

[61653 HTAFC]

A similar style of sloping bridge on either the M5 or A30/A38 has signs on the hardshoulder only. I cant remember where but it was between Bristol and Cornwall - I cant remember which road its on.
Do we know the height of the bridge?

I know the one you mean, it's on the M5 near Weston Super Nightmare.

 

[jon0844]

Been like this for as many years as I can remember

Streetview confirms this. Any idea why it would be left like that for so long? Was it forgotten about or the money to finish (or even start) the job spent somewhere else?

 

[IanD]

Streetview confirms this. Any idea why it would be left like that for so long? Was it forgotten about or the money to finish (or even start) the job spent somewhere else?

I seem to recall that the 'temporary' fencing was added to increase the height of the original maybe to stop people throwing stuff or jumping off.

 

[Hadders]

Thankfully no-one's been seriously hurt but I do find it concerning that the 'load' on a trailer striking a bridge causes it to collapse.

 

[richw]

Thankfully no-one's been seriously hurt but I do find it concerning that the 'load' on a trailer striking a bridge causes it to collapse.

I'm not convinced, as pointed out above there is a gantry a few yards before at the same height. How did it miss that? I'm suspecting coincidence that the tall load was nearby.

Possibly cemented by no arrests, the driver if at fault would at least be done for an unsafe load.

 

[Gathursty]

Where on a footbridge like this would be it's structural weak points?
Who in the construction industry would know the answer to the above question?
How long has there been discussion over schemes requiring altering or removal to this bridge?
Which groups/businesses would have a vested interest in the removal of this bridge?

 

[richw]

I gather from other websites The part that fell was a seperate 'beam deck' resting on load bearing ledges, which has been dislodged from those ledges with a knock. The deck beam would likely be one part bought in ready made and craned into position at construction

 

[Peter Mugridge]

the break in the bridge seems to have a clean cut.

A lot of these bridges seem to be made of two sections with a joint similar in appearance to a CWR expansion joint in the middle - so I would expect a clean looking break if one half came down but not the other half.

 

[swt_passenger]

A lot of these bridges seem to be made of two sections with a joint similar in appearance to a CWR expansion joint in the middle - so I would expect a clean looking break if one half came down but not the other half.

I think the usual design is three sections, a cantilever extended from either side out over (and mounted on) a pier, and a central beam that basically just sits on the two cantilever's ends. So you'd expect a joint over each carriageway of a motorway or dual carriageway.

I noticed that discussion in a 'roads' forum (SABRE) suggests they are not actually designed to resist an impact, but by design are supposed to give a greater clearance than the usual minimum. A pertinent question is whether or not that extra clearance extends right across the hard shoulder, as many footbridges seem to slope upwards towards the centre.

 

[edwin_m]

By moving back and forth from the Google link someone posted further back, it can be seen that the section of the span above the eastbound carriageway is integral with the south pier, so cantilevered right across its carriageway. The westbound part that has come down rests on this via a stepped joint roughly above the central reservation. The imagery isn't clear enough to know for certain, but it would be logical for there to be a similar joint near the westbound hard shoulder, or for this end to be supported directly by the pier. So it appears this span has lifted off its two supports to come down in the road.

I would think a significant impact would be needed to dislodge it, as surely it would be pinned in some way rather than just resting?

Hard to tell, but by zooming a view from well to the east to minimise parallax , I think the footbridge is lower over the hard shoulder than the gantry immediately before it. So something could conceivably pass under the gantry and hit the footbridge.

 

[Peter Mugridge]

This raises two points:

1) How common are bridges which are lower over the hard shoulder than over the true carriageway? Given the increasing move to regard the hard shoulder as a cheap way of building an extra running lane, have these clearance issues been taken into account? Particularly since anything carrying an abnormal load is more likely to be staying towards the nearside by default.

2) Are diggers and similar generally being loaded with due regard to keeping their heights as low as possible or are they being loaded in the most convenient way for the purposes of getting them on whatever is carrying them? There is a difference...

 

[jon0844]

I read a post on another forum saying that this section is to become all lane running and the bridge was low enough on the hard shoulder to require the lane to be closed if and when it proceeded.

So the clearance must be less, which begs the question why there's a hard shoulder there now. Surely it would be removed, with barriers, a long section of road markings, signs etc. Many other bridges on widened motorways have this.

 

[Peter Mugridge]

I read a post on another forum saying that this section is to become all lane running and the bridge was low enough on the hard shoulder to require the lane to be closed if and when it proceeded.

That sounds like a recipe for congestion disaster - surely the whole point of this all lane running thing ( and idea with which I completely disagree on safety grounds ) is to provide an extra lane to deal with traffic volume; if the extra lane has to re-merge with the next lane every so often it's going to cause congestion hot spots prior to each such pinch point.