Great Western Main Line electrification - ongoing discussion

[whole diary]

[martyjon]

Good picture in this evening's Bristol Post, showing the state of electrification at Hatchet Road (just after Bristol Parkway):

Image from Bristol Post
Incidentally, I can't help noticing that this is another bridge where the height warning is given in US Customary units only - is there a pattern emerging here? https://goo.gl/maps/uEs1mQrrHaC2

Open Top Rail Replacement Services now, might be a first. Luckily there were no passengers on board.

[Bmblbzzz]

Full marks to the "huge steel barrier," which worked as intended.

The bus hit the bridge with such force that the roof of the bus was sheared clean off, and the bus continued on for a few more yards before coming to a stop.

A few more yards? It looks like about three bus lengths from the point where it first hit the bridge.

[stuving]

Full marks to the "huge steel barrier," which worked as intended.

The full quote is "An initial inspection of any impact damage to the bridge revealed the bridge came through the experience unscathed - a huge steel barrier at the entrance to the bridge took the full force of the bus's roof, and protected the bridge as intended."

Well, they are still running trains over that "barrier" - it's the the northern, steel, bridge put there some time after the Severn Tunnel and the line from Wootton Bassett were built. That is 15'2" up, which is plenty to take a double-decker under - so it didn't hit it. It hit the brick arch, having failed to move out to the middle of the road, which is why the roof in the picture on Bristol Live lies under the steel bridge. Draw your own conclusions about the reporting!

[BBM]

BBC^» (British Broadcasting Corporation - home page) News has a video of the actual incident involving the bus hitting the bridge:

https://www.bbc.co.uk/news/uk-england-bristol-46077532

[SandTEngineer]

Full marks to the "huge steel barrier," which worked as intended.

The full quote is "An initial inspection of any impact damage to the bridge revealed the bridge came through the experience unscathed - a huge steel barrier at the entrance to the bridge took the full force of the bus's roof, and protected the bridge as intended."

Well, they are still running trains over that "barrier" - it's the the northern, steel, bridge put there some time after the Severn Tunnel and the line from Wootton Bassett were built. That is 15'2" up, which is plenty to take a double-decker under - so it didn't hit it. It hit the brick arch, having failed to move out to the middle of the road, which is why the roof in the picture on Bristol Live lies under the steel bridge. Draw your own conclusions about the reporting!

Information posted elsewhere suggests there isn't a bridge protection beam there and the bus hit the brick arch after clearing the parallel steel span.

[Red Squirrel]

Full marks to the "huge steel barrier," which worked as intended.

The full quote is "An initial inspection of any impact damage to the bridge revealed the bridge came through the experience unscathed - a huge steel barrier at the entrance to the bridge took the full force of the bus's roof, and protected the bridge as intended."

Well, they are still running trains over that "barrier" - it's the the northern, steel, bridge put there some time after the Severn Tunnel and the line from Wootton Bassett were built. That is 15'2" up, which is plenty to take a double-decker under - so it didn't hit it. It hit the brick arch, having failed to move out to the middle of the road, which is why the roof in the picture on Bristol Live lies under the steel bridge. Draw your own conclusions about the reporting!

Information posted elsewhere suggests there isn't a bridge protection beam there and the bus hit the brick arch after clearing the parallel steel arch.

As you suggest there clearly isn't a CPB - this is the view from where the bus entered:

https://goo.gl/maps/e1N696vDEnp

...and this is the view from the other side:

https://goo.gl/maps/QfoiS3VqA312

Edit: corrected Google Maps links

[martyjon]

Full marks to the "huge steel barrier," which worked as intended.

The full quote is "An initial inspection of any impact damage to the bridge revealed the bridge came through the experience unscathed - a huge steel barrier at the entrance to the bridge took the full force of the bus's roof, and protected the bridge as intended."

Well, they are still running trains over that "barrier" - it's the the northern, steel, bridge put there some time after the Severn Tunnel and the line from Wootton Bassett were built. That is 15'2" up, which is plenty to take a double-decker under - so it didn't hit it. It hit the brick arch, having failed to move out to the middle of the road, which is why the roof in the picture on Bristol Live lies under the steel bridge. Draw your own conclusions about the reporting!

Information posted elsewhere suggests there isn't a bridge protection beam there and the bus hit the brick arch after clearing the parallel steel arch.

As you suggest there clearly isn't a CPB - this is the view from where the bus entered:
https://goo.gl/maps/e1N696vDEnp
...and this is the view from the other side:
https://goo.gl/maps/QfoiS3VqA312
Edit: corrected Google Maps links

.... and very apt that the second link should show a double decker turning right into the Bristol Parkway Estate.

[ellendune]

When approached from the north side there are no white lines on the bridge to point out the need to be in the centre of the road.

[stuving]

When approached from the north side there are no white lines on the bridge to point out the need to be in the centre of the road.

That's true - and I'm sure there should be. But look left from the initial Street View and there's a roadside sign, plus a dashed line on the road. However, given that the first bridge hides the second, I'd expect words and arrows on the road too (plus those width lines). Note that from the other side there is no line on the road, though there is the same roadside sign.

[paul7575]

Good picture in this evening's Bristol Post, showing the state of electrification at Hatchet Road (just after Bristol Parkway):

Incidentally, I can't help noticing that this is another bridge where the height warning is given in US Customary units only - is there a pattern emerging here? https://goo.gl/maps/uEs1mQrrHaC2

Streetview shows that there are advance signs in both metric and imperialunits on the approach, and also instructions to use the centre of the road.

Paul

[stuving]

The rules - Traffic Signs Manual: Chapter 4 - say this about composite bridges:

COMPOSITE BRIDGES
7.25 Some bridges originally built as arches have been adapted with the addition of girders or beams. Where the arch is the lowest part, the whole structure should be signed as an arch bridge. Black and yellow striped plates (to highlight the profile of the arch) should be suspended from the bridge beam, together with further plates on the arch itself.

The signage it specifies for an arch bridge of this width includes a single chord (as on the north side) plus the roadside signs at the bridge which look right. There should also be advance signs and "route avoiding" arrows on other signs; I din't know if they are present here.

How often do you see an arch-shaped dangly thing under a bridge? Not often! The manual has more to say about them (straight ones are also used):

7.27 Experience has shown that these suspended plates will themselves be struck from time to time and that rigidly-mounted aluminium substrates are not suitable. Rubber or other flexible material should be used for the backing, suspended by means of chains or hinges fixed securely to the bridge structure by a method agreed with the bridge owner. The plates should not be fixed rigidly by screws or bolts to the face of the bridge, as there is a greater risk than with flexibly-suspended plates of them being dislodged and falling onto vehicles on the road beneath. The use of rubber-backed plates will help to avoid annoyance to nearby residents from the noise of hanging metal plates striking the bridge structure in wind or vehicle slipstream. It is recommended that the yellow parts of the marking should be retroreflective; they may also be fluorescent (see para 7.6). When the signs are lit, the plates should also be lit whenever practicable. This is particularly helpful where a girder bridge is followed by a more restrictive arch bridge.

And finally, road markings, which are in TSM^▸ (Track Section Manager) Chapter 5:

HIGH VEHICLE MARKINGS AT ARCH BRIDGES
22.5 All bridges with a headroom of less than 16'-6"should be clearly signed. (Arch bridge signing is dealt with in Chapter 4, paras 7.16 to 7.19). Road markings, together with appropriate warning signs,can be used in the case of arch bridges to guide higher vehicles to the centre of the road, where the clearance may be greater than at the outside edges.

22.6 The HIGH VEHS marking (diagram 1024.1) is prescribed for use at arch bridges. High vehicles should be guided through the highest part of the arch using this marking and the arrow to diagram 1014, together with edge of carriageway markings to diagram 1010. These should be aligned with the chord marking on the bridge (diagram 532.2) which indicates the available headroom in the central part of the road...

Note: the current chapter 5 is dated 2003, so its references to chapter 4 are out to date - that is now the 2013 edition.

[stuving]

Good picture in this evening's Bristol Post, showing the state of electrification at Hatchet Road (just after Bristol Parkway):

Incidentally, I can't help noticing that this is another bridge where the height warning is given in US Customary units only - is there a pattern emerging here? https://goo.gl/maps/uEs1mQrrHaC2

Streetview shows that there are advance signs in both metric and imperialunits on the approach, and also instructions to use the centre of the road.

Paul

For arch bridges the meaning of "advance" is a bit puzzling, since they are doing two things. At the bridge, the main concern is getting vehicles into the right bit of the road. At the last turning, or in advance, the concern is to prevent overheight vehicles going that way and diverting them. So the inserts within advance direction signs are the same as other low bridges, while the markings and the "final warning sign" (use middle of road) are specific to arches. But then, for some reason, single triangular signs at the last turning (with no "route avoiding" message) or further away have a little arch in them. Since that last turn can be miles back (needing a distance label) or right up close (as in Hatchet Lane), they may or may not be "in advance". Anyway, what I meant was something at least half a mile away.

[Red Squirrel]

Good picture in this evening's Bristol Post, showing the state of electrification at Hatchet Road (just after Bristol Parkway):

Incidentally, I can't help noticing that this is another bridge where the height warning is given in US Customary units only - is there a pattern emerging here? https://goo.gl/maps/uEs1mQrrHaC2

Streetview shows that there are advance signs in both metric and imperialunits on the approach, and also instructions to use the centre of the road.

Paul

Yes, the advanced signs use both sets of units, but the warnings on the bridge itself are in USCS only. Overall, it could be clearer.

[johnneyw]

Good picture in this evening's Bristol Post, showing the state of electrification at Hatchet Road (just after Bristol Parkway):

Incidentally, I can't help noticing that this is another bridge where the height warning is given in US Customary units only - is there a pattern emerging here? https://goo.gl/maps/uEs1mQrrHaC2

Streetview shows that there are advance signs in both metric and imperialunits on the approach, and also instructions to use the centre of the road.

Paul

Yes, the advanced signs use both sets of units, but the warnings on the bridge itself are in USCS only. Overall, it could be clearer.

Is it just me or did the footage remind anyone else of the double decker bus in Live and Let Die?

[stuving]

There doesn't seem to be any simple way of finding out where signs are mandatory, but the form they should take if present is prescribed (the word used) in The Traffic Signs Regulations and General Directions 2016. The Traffic Signs Manual generally repeats this in something resembling comprehensible English (which the TSRGD 2016 are not), but are all older than 2016 so may no longer be correct.

In the case of units on bridge signage, I found a Sunday Times report that a 2014 DfT^» (Department for Transport - about) consultation proposed making dual units compulsory on new signs but let old ones stay. That's consistent with the 2013 TSM^▸ (Track Section Manager) saying metric is optional, and the TSRGD 2016 only showing the signs with both - but I wouldn't put it any stronger than that. Distances (along the road) are of course still to be given in miles.