Bridge parapets over railways stronger than motorways

[blueberry11]

Is there a reason why a road bridge parapets (or crash barriers, idk the terminology) are stronger when its over a railway than a motorway (or other large drop like a valley or river)? Is there a difference between 100,000 vehicles per day at 65 mph vs 70 trains at 90 mph over the same period? I feel like they should be the same used as the one over motorways. I do think these railway parapets even stop the largest vehicles going 55 mph (the maximum speed allowed for HGVs)?

The relevant requirements is listed at the Design Manual for Roads and Bridges (DMRB) CD 377 - Requirements for road restraint systems, especially section 4, page 39

 

[ac6000cw]

I think the restraint/protection standards for road-over-rail bridges were revised upwards in the aftermath of the Great Heck accident in 2001 - https://en.wikipedia.org/wiki/Selby_rail_crash - when a Land Rover Defender towing a heavy trailer careered off the M62 at an overbridge over the ECML and ended up on the track. This caused a very serious accident involving two trains (one passenger and one freight) which killed 10 people (including both train drivers) and seriously injured 82.

 

[King Lazy]

I know nothing of the subject but my own logic would be it’s a numbers game. And I suspect not just deaths but people potentially involved.

So if a vehicle with 4 persons in leaves a bridge over a valley you would have 4 persons involved.

If it leaves a bridge over a motorway you could have at the better end of outcomes a situation where other vehicles can quickly stop and still 4 persons involved.

Worse case might be it lands in front of a full coach which hits the vehicle and a coach behind also impacts. c53+53+4 for 110 involved.

Most traffic in normal weather can stop quickly before compounding an incident. That’s why two vehicle crashes don’t always turn into 50 vehicle pile ups.

But if the vehicle goes onto a railway, it can now potentially be in the path of a train with c700 passengers which by the time the driver sees the incident is unable to stop.

If this train then derails and is hit by another with 700 passengers you have 1400 people who have been involved.

I’m sure it’s just risk assessment of potential severity of outcome.

 

[blueberry11]

I didn't think of the fact that a vehicle leaving a motorway onto a railway is a very high risk assessment and worse outcome. That DMRB document may be worth a read, but its over 100 pages long. Maybe also the fact that trains are not supposed to stop within 'the distance they see is clear', which is what road traffic uses as they are controlled by signals instead. So a truck that has fallen onto the railway would be game over. Also think about the 25kV wires/750V third rail.

Alternatively, the railway can run over the road instead, removing the need for these strong parapets. I think that is preferable than a road over railway and should be done if feasible.

But then this go back to the question where railway parapets can withstand a 44t HGV (maximum weight legally permitted) going 55 mph. They (normally) can't withstand a normal metal barrier but concrete barriers should be able to contain a HGV, hence why our motorways are increasingly using them.

 

[edwin_m]

They (normally) can't withstand a normal metal barrier but concrete barriers should be able to contain a HGV, hence why our motorways are increasingly using them.

This is particularly on the central reservation. A vehicle (particularly a large one) crossing into the opposite carriageway is potentially a very serious accident.

 

[snowball]

The answer is in ac6000cw's post.

Not only were the standards for road parapets upgraded after the Great Heck, but a lot of existing bridges had their barriers upgraded to meet them (something that doesn't always happen when standards are changed).

 

[Ploughman]

Am I right in thinking that the gap in the barriers at the Heck site, is still there?

 

[The exile]

Alternatively, the railway can run over the road instead, removing the need for these strong parapets. I think that is preferable than a road over railway and should be done if feasible.

Unless you're building both from scratch, you're very rarely going to have a choice. Even when replacing a level-crossing, taking the road under the railway throws up all kinds of potential drainage problems.

 

[blueberry11]

Unless you're building both from scratch, you're very rarely going to have a choice. Even when replacing a level-crossing, taking the road under the railway throws up all kinds of potential drainage problems.

Melbourne's level crossing closure program - I'm I a joke to you? They are pretty much doing that, but on a large scale.

 

[61653 HTAFC]

I think the restraint/protection standards for road-over-rail bridges were revised upwards in the aftermath of the Great Heck accident in 2001 - https://en.wikipedia.org/wiki/Selby_rail_crash - when a Land Rover Defender towing a heavy trailer careered off the M62 at an overbridge over the ECML and ended up on the track. This caused a very serious accident involving two trains (one passenger and one freight) which killed 10 people (including both train drivers) and seriously injured 82.

Parapet strength is irrelevant to what actually happened at Great Heck though, the road vehicle left the carriageway in advance of the bridge and went down the embankment. It did not break through the bridge parapet and fall directly onto the railway, as your wording suggests.
If we're talking parapet strength, that cement wagon that fell off a bridge onto a 455 (Oxshott?) is more relevant.

 

[dosxuk]

It did not break through the bridge parapet and fall directly onto the railway, as your wording suggests.

It didn't break through, but @ac6000cw is correct, they did revise the standards after the Great Heck accident, including many locations which had bridges altered to bring them up to standard. The bridge involved was modified - to increase the distance that was barriered to make it far more difficult for an errant vehicle to end up on the wrong side and on the railway.

 

[edwin_m]

Melbourne's level crossing closure program - I'm I a joke to you? They are pretty much doing that, but on a large scale.

This is saying Melbourne has a huge number of level crossings and a large-scale systematic elimination programme. The UK has neither, and it is unheard of to elevate or lower the railway purely to eliminate level crossings. As the link notes, each crossing eliminated in this way requires re-building of around 1km of railway above or below grade. Because roads can manage steeper gradients, re-building the road is usually cheaper and elevating it is cheaper than lowering it. There may well be acceptability issues with putting a road - or a railway - on a viaduct or in a trench, and this will also be a major factor in how to eliminate a crossing or whether it can be eliminated at all. .

Anyway, parapet safety won't be a significant issue in the decision whether to put the railway over the road or vice versa. In a typical case you could probably make a road parapet ten feet high and five feet thick and it would still be cheaper than putting the road under the railway.

 

[ac6000cw]

It did not break through the bridge parapet and fall directly onto the railway, as your wording suggests.

I know that (and I didn't say that it broke through the parapet - I said 'at an overbridge' not 'off an overbridge'). The point I was making was that (very serious) accident caused a review of the protection standards.

 

[blueberry11]

This is saying Melbourne has a huge number of level crossings and a large-scale systematic elimination programme. The UK has neither, and it is unheard of to elevate or lower the railway purely to eliminate level crossings. As the link notes, each crossing eliminated in this way requires re-building of around 1km of railway above or below grade. Because roads can manage steeper gradients, re-building the road is usually cheaper and elevating it is cheaper than lowering it. There may well be acceptability issues with putting a road - or a railway - on a viaduct or in a trench, and this will also be a major factor in how to eliminate a crossing or whether it can be eliminated at all. .

Anyway, parapet safety won't be a significant issue in the decision whether to put the railway over the road or vice versa. In a typical case you could probably make a road parapet ten feet high and five feet thick and it would still be cheaper than putting the road under the railway.

But the road under the railway have clearances as low as 2m (6'6") while for a railway, its like 6m (19"8') or 5m (16"6') if you don't wires to run underneath it. Due to the potential for electrification, all new bridges over railways have to be 6m I think (at least for those not using third rail?). I also think the parapets for bridges have to be checked during electrification works even if the bridge doesn't get modified/rebuilt as they may have stricter requirements than a non-electrified one.

Regarding level crossing closures, the one at Ely was closed because one, there's too many trains using it; 2, a new bypass was built for that reason and 3, many trucks hit the low bridge sign (the level crossing had a low bridge bypass close by). I also see a strong parapet that even large trucks cannot break through. But that's nothing compared with what Melbourne is doing, although Network Rail states that over 1300 level crossings were removed since 2010 (but the majority of them are either footpath crossings or minor private roads, not public highway crossings). May also why UK level crossings tend to not be within city limits. Like I don't see any in Norwich.

 

[snowball]

I'm

But the road under the railway have clearances as low as 2m (6'6") while for a railway, its like 6m (19"8') or 5m (16"6') if you don't wires to run underneath it. Due to the potential for electrification, all new bridges over railways have to be 6m I think (at least for those not using third rail?). I also think the parapets for bridges have to be checked during electrification works even if the bridge doesn't get modified/rebuilt as they may have stricter requirements than a non-electrified one.

Regarding level crossing closures, the one at Ely was closed because one, there's too many trains using it; 2, a new bypass was built for that reason and 3, many trucks hit the low bridge sign (the level crossing had a low bridge bypass close by). I also see a strong parapet that even large trucks cannot break through. But that's nothing compared with what Melbourne is doing, although Network Rail states that over 1300 level crossings were removed since 2010. May also why UK level crossings tend to not be within city limits. Like I don't see any in Norwich.

I'm not quite sure what point you're trying to make in this post.

When level crossings are eliminated in the UK, the number of new bridges created is usually much less than the number of level crossings eliminated. The road at a level crossing is often a minor one or a private access. Sometimes roads can be closed without replacement; sometimes roads can be diverted to use existing bridges on other roads. If there are no existing bridges nearby, several roads can be combined and put over one new bridge.

It's vastly easier and cheaper to realign, raise or lower a road than a railway. It's usually much easier and cheaper to put a road over an existing railway than under it.

None of this has anything to do with motorways as suggested in your OP, as motorways never have level crossings anyway.

 

[zwk500]

But the road under the railway have clearances as low as 2m (6'6") while for a railway, its like 6m (19"8') or 5m (16"6') if you don't wires to run underneath it. Due to the potential for electrification, all new bridges over railways have to be 6m I think (at least for those not using third rail?). I also think the parapets for bridges have to be checked during electrification works even if the bridge doesn't get modified/rebuilt as they may have stricter requirements than a non-electrified one.

A new road under the railway would start with a default clearance of 5m (16'6"). You would need to provide compelling evidence to reduce that headroom, which is going to be hard on most highways as the risk of a bridge strike is obviously greater if the clearance is less. You've also got to consider the risk of flooding a road if it suddenly dips (as the road near Manchester Airport keeps showing).
Building under something is also generally more disruptive as you've got to dig out the old rail formation to put in the new bridge (although some techniques like bridge slides can minimise this), whereas lifting a structure over only needs a short possession (assuming the piers/abutments can be built without disruption).

Regarding level crossing closures, the one at Ely was closed because one, there's too many trains using it; 2, a new bypass was built for that reason and 3, many trucks hit the low bridge sign (the level crossing had a low bridge bypass close by). I also see a strong parapet that even large trucks cannot break through. But that's nothing compared with what Melbourne is doing, although Network Rail states that over 1300 level crossings were removed since 2010. May also why UK level crossings tend to not be within city limits. Like I don't see any in Norwich.

NR counts footpaths as level crossings as well. The majority of closures have likely been footpath/bridleways where a relatively lightweight structure can be put in to preserve access without land buying or road building. Melbourne has funded a fair number of it's removals from a one-off windfall connected to selling it's port, and is linked to several station openings and a general upgrade of the metro area. It's certainly possible to remove level crossings, but trying to compare a city metro to a national network isn't really sensible. the London Underground has, AIUI, single figure level crossings, by way of comparisons.

 

[The exile]

Melbourne's level crossing closure program - I'm I a joke to you? They are pretty much doing that, but on a large scale.

I was idly looking at the sites of some of these crossings on Street View earlier (don't tell the boss!) - and what struck me was the amount of space available around them. I'd love to see how Melbourne's planners would deal with somewhere like Lincoln High Street if closure to traffic (which I see is what has actually happened) were not an option:

Street View · Google Maps

Explore a place in a more immersive way in Google Maps.

www.google.co.uk

There will be plenty of urban crossings which are equally "hemmed in" where closure to traffic is not an option....