Railway bridges struck by road vehicles - merged topic, ongoing discussion

[whole diary]

[patch38]

I'm pretty certain there is an overheight sensor and warning equipment on the western approach (i.e. coming from Mannington roundabout/John Lewis). I don't recall seeing any in the other direction (from the Dick Lovett side), and that's the way this truck was heading. I'll take a look at stupid-o'clock tomorrow as I pootle to the station.

[tomL]

This brought Swindon to a standstill this morning, trains, cars and buses. It didn't help the diversion was through the now long running joke that is the Bruce Street Bridges works. 

[stuving]

It, erm, strikes me that at 14' 9' or 4.5m, that this bridge is particularly at risk, as the standard unmarked bridge height is 16' 6" or 5.1m, so really quite close in height to this one.

That's true, but not for drivers - there's a 3" minimum clearance that is allowed by reducing the signed height. The Rules (Traffic Signs Manual Chapter 4: Warning Signs) say:

7.11 The imperial figure shown on signs to indicate the available headroom should be at least 3 inches less than the measured height to allow a safety margin. If the resulting figure is not a multiple of 3 inches, it should be rounded down to the nearest lower multiple of 3 inches.

Example 1: measured height 15'-2", subtract 3" to create a safety margin 14'-11", round down to nearest multiple of 3" and sign as 14'-9".
Example 2: measured height 14'-6", subtract 3" to create a safety margin 14'-3", and sign as 14'-3" (rounding down not required as already expressed to the nearest 3")

Thus, the maximum headroom that will normally appear on a sign is 16'-0".

But what was the logic behind saying "this bridge is particularly at risk"? I guess it's that a driver might spot lower low bridges as too low just by eye, but this one would not stand out so much. Whether that's reason enough to concentrate efforts to heighten bridges on such high low bridges in particular I'm not so sure. 

[ellendune]

Given the number of hits this bridge has taken over the past few years, I'm surprised the local authority and Network Rail haven't considered reducing the carriageway height by a couple of feet to cure this problem.

I am not sure that would work there is a flood spot nearby at the Running Horse Pub. Lowering the road here by 2ft might just be enough to cause flooding here.

[Rob on the hill]

I'm pretty certain there is an overheight sensor and warning equipment on the western approach (i.e. coming from Mannington roundabout/John Lewis). I don't recall seeing any in the other direction (from the Dick Lovett side), and that's the way this truck was heading. I'll take a look at stupid-o'clock tomorrow as I pootle to the station.

I noticed a while ago, what I believe is the sensor on the Mannington side, appeared to have been knocked and was leaning at an angle. Having passed it tonight it is still leaning, so perhaps it may not have been working properly?

[stuving]

I'm pretty certain there is an overheight sensor and warning equipment on the western approach (i.e. coming from Mannington roundabout/John Lewis). I don't recall seeing any in the other direction (from the Dick Lovett side), and that's the way this truck was heading. I'll take a look at stupid-o'clock tomorrow as I pootle to the station.

I noticed a while ago, what I believe is the sensor on the Mannington side, appeared to have been knocked and was leaning at an angle. Having passed it tonight it is still leaning, so perhaps it may not have been working properly?

Google Street View (date July 2015) shows detectors and warning signs on the A3102 both ways. It also shows the collision protection beams bolted onto the abutments - belt and braces, as it were. But they work - I don't think the trains were delayed at all. 

DfT^» (Department for Transport - about) have a page linking to several guides on low bridges and how be nice to them. The truck driver's guide says:

You should be aware that traffic signs are provided at bridges to show the maximum permitted vehicle height when less than 16 ́-3 ̋ (4.95 metres).

That's less than the 16'6"" (5.03 m) due to that 3" clearance.

The "Protocol for Highway Managers & Bridge Owners" explains about protection measures:

B.5 Variable message signs (VMS) with height detection equipment
B.5.1 Infra red beams are placed in advance of the bridge and are set at the restricted signed height so that they activate the sign if the beam is broken by an overheight vehicle. The activated sign provides a warning so that the driver of the offending vehicle is given the opportunity to stop and
divert.
B.5.2 Sufficient distance is necessary for beam and sign to be located in advance of the bridge both for the sign to respond and for the driver to read and react to its message. To maximise the effectiveness of VMS through positioning, consider:
^ locating the signs in advance of a point where drivers can
easily re-route, ideally without having to turn around
^ positioning the signs away from junctions, roundabouts or other complex situations and large light sources or distractions Consideration should be given to whether parking restrictions are required so that neither the sign nor the detector is obscured by parked vehicles.
...
B.5.4 Infra red beams can suffer from malfunction due to beam misalignment and so it is essential to have a clear default message indicating when the sign is not working. It is recommended that signs are remotely monitored to identify any malfunction.
B.5.5 Each installation should have a robust maintenance contract which includes an emergency response requirement to deal with a malfunction.

How easy is it going to be to comply with both of those two points to consider at once?

And:

B.2 Collision protection beams (CPBs)
B.2.1 Collision protection beams are installations designed to absorb the force from an impacting vehicle and so protect the structure of a bridge. As such they are generally built into the existing bridge abutments because the Highways Act 1980 does not permit free standing supports over the highway as they would create an additional and avoidable hazard to traffic.
...
B.2.4. Collision protection beams to a flat soffit bridge should be erected between 10 - 20 mm lower than the actual bridge soffit (See BD6510) and so the headroom clearance must be rechecked and any necessary adjustments made to the signing before traffic is allowed access under the bridge. The promoter of the protection scheme should allow for and meet the cost of any related re-signing.

I'm not convinced by that reference to the Highways Act 1980. I presume it means section 178, which says (in part):

178 Restriction on placing rails, beams etc. over highways.
(1)No person shall fix or place any overhead beam, rail, pipe, cable, wire or other similar apparatus over, along or across a highway without the consent of the highway authority for the highway, and the highway authority may attach to their consent such reasonable terms and conditions as they think fit.
...
(5)This section does not apply to any works or apparatus belonging to any statutory undertakers...

Since railways usually count as statutory undertakings, this appears not to be a blanket ban on beams across roads on two counts.

[chrisr_75]

But what was the logic behind saying "this bridge is particularly at risk"? I guess it's that a driver might spot lower low bridges as too low just by eye, but this one would not stand out so much. Whether that's reason enough to concentrate efforts to heighten bridges on such high low bridges in particular I'm not so sure. 

That was exactly my logic! The fact it's only just a low bridge I suspect tempts people to have a go - perhaps fatigue, unfamiliar vehicle, time pressure, inexperienced drivers or those unfamiliar with the area could be contributory factors (but not really an excuse of course!). I was mostly just postulating out loud, so please forgive any technical oversights or pie in the sky ideas!

This bridge seems to be particularly vulnerable as its been hit repeatedly over recent years and obviously carries a significant transport link in the GWML^▸ (Great Western Main Line) and is on a main arterial road through Swindon - given the disruption bridge strikes cause here it would seem sensible to me to mitigate the risk of further bridge strikes at this particular location.

I did look on google street view and didn't see any evidence of overheight sensors or signs, so apologies for missing that! Would seem sensible to me if those sensors were linked to the traffic lights either side of the bridge - a red light is usually pretty unambiguous and requires no thought for most drivers to respond to, but I'm sure some regulations or another, as you have highlighted, would preclude that.

[stuving]

I did look on google street view and didn't see any evidence of overheight sensors or signs, so apologies for missing that! Would seem sensible to me if those sensors were linked to the traffic lights either side of the bridge - a red light is usually pretty unambiguous and requires no thought for most drivers to respond to, but I'm sure some regulations or another, as you have highlighted, would preclude that.

The sensors are well before the bridge, to give enough time to see the sign and manoeuvre to turn left. I think the signs say "TURN LEFT" - obviously they are not illuminated in Street View, but that didn't stop one of them getting pixellated anyway.

[grahame]

The fact it's only just a low bridge I suspect tempts people to have a go ...

Running places where the public can come and where we have lots of visitors over the years

* Very tall people are so used to ducking that they always do
* Very low clearances are so obviously duck-unders that everyone stoops
... and it's those who are just a bit too tall for a slightly low lintel who are knocking their heads

[patch38]

28 Jan - The sensor on the Mannington side still appears to be pointing skywards as Rob mentioned earlier.

[TonyK]

Even if it is just a few inches too low for the lorry, the driver has the ultimate responsibilty for the incident. The operator of the lorry can also be culpable. Routes should be planned with low bridges (and weight limits, power cables, narrow lanes etc) in mind before anyone starts the engine. Software exists to enable freight operators to do exactly that.

[chrisr_75]

Even if it is just a few inches too low for the lorry, the driver has the ultimate responsibilty for the incident. The operator of the lorry can also be culpable. Routes should be planned with low bridges (and weight limits, power cables, narrow lanes etc) in mind before anyone starts the engine. Software exists to enable freight operators to do exactly that.

It is also mandatory for all tall vehicles (I'm not 100% sure above what height this becomes mandatory) to have their overall height clearly marked and visible from the driving position - I would assume any missing labels would result in a roadworthiness test fail.

[eightf48544]

Interesting quote from a previous post on collision protection beams having to be bolted to the bridge abutments:

"the Highways Act 1980 does not permit free standing supports over the highway as they would create an additional and avoidable hazard to traffic."

Don't understand why would they be an additonal and avoidable hazard to traffic. Surely the whole point is to take the top off a too high a vehicle before it hits the bridge. The Germans don't have any such qualms, I first saw very substantial  free standing beams (RSJs^▸ (Rolled Steel Joist, which can also be called )) in Magdeburg in 1996. They also ahve 600 V tram wires as well on other low bridges!

Please explain.

[stuving]

Interesting quote from a previous post on collision protection beams having to be bolted to the bridge abutments:

"the Highways Act 1980 does not permit free standing supports over the highway as they would create an additional and avoidable hazard to traffic."

Don't understand why would they be an additonal and avoidable hazard to traffic. Surely the whole point is to take the top off a too high a vehicle before it hits the bridge. The Germans don't have any such qualms, I first saw very substantial  free standing beams (RSJs^▸ (Rolled Steel Joist, which can also be called )) in Magdeburg in 1996. They also ahve 600 V tram wires as well on other low bridges!

Please explain.

I've seen the same thing said about their not being allowed in other places, but as the rest of that post shows I can't trace it to the act in question. But, being literal (or legalistic) a separate portal would be a hazard - it's an obstruction the same height as a bridge which is one - it is additional - not part of the bridge - and avoidable in the sense that you can build the bridge, and have it perform its purpose, without one.

[TonyK]

There is an obvious answer - build another bridge, just before the existing one.