Underbridge/Overbridge? Wondering free...

[61653 HTAFC]

Apologies for the Wombles reference, I couldn't resist!

Something about railway parlance that has always bugged me, and which I've never been able to find a definitive answer, is which is the correct term to use for bridges over and under the railway:
A bridge which carries the railway formation on its deck, passing over a road- is this an overbridge (in that it carries the railway over something) or an underbridge (in that the bridge crosses something which goes under the formation)? I'm fairly sure I've heard both being used at various times, and as a result am never sure which is being used unless I know the location.

Basically what I'm hoping to nail down is whether the correct term refers to the position of the railway in relation to the bridge, or the position of the bridge in relation to the railway. Of course, I won't be hugely surprised if the answer is "it depends who you ask!"

 

[GB]

I am sure I have heard both terms as "rail overbridge" and "road overbridge".

 

[Baxenden Bank]

rail over road bridge = road under rail bridge.

Perhaps it depends not on who you ask, but who is doing the bridging (or paying for the bridge).

Should 'ground level' come into it? If you have a road or railway at ground level and then go below it to create a new crossing do you create an underbridge, and if you go over the top, you create an overbridge?

 

[61653 HTAFC]

Perhaps I should have been clearer...

My issue is what the correct terminology is from the point of view of the railway. For example if describing a railway route which has a bridge carrying a road over the railway, is this an Overbridge (because something goes over the railway) or an Underbridge (because the railway goes under something)? As I said, I've heard both being used so unless I know the location well, I'm not sure which a person means. Essentially I guess I'm asking whether the railway is linguistically active or passive when it comes to describing grade-separated crossings. Roll on summer so I can get out of the house instead of wondering about such trivial matters!

@Baxenden Bank for the time being, ground level is irrelevant to my quandary, just the level of the railway in relation to the level of whatever is being crossed.

 

[High Dyke]

In respects of bridge strikes they are termed overline bridges (road crossing above a railway) or underline bridges (road crossing below a railway), for the benefit of the Rule Book..

 

[Western Sunset]

From a railway viewpoint. Overbridge carries something over the railway; underline being the opposite. Hence often in the literature about loco restrictions, it would often mention weak underline bridges, ie the railway being on the bridge bit.

 

[swt_passenger]

Ellis’ railway encyclopaedia defines “underbridge“ as a bridge allowing passage beneath the railway, and “overbridge” allowing passage over the railway, then cross references to “underline bridge” and “overline bridge“ as the alternative names, but they’re also explained as helping to avoid the confusion caused by highway engineers who use the opposite terminology.

 

[snowball]

I'm not a trained engineer but I've been reading stuff written by and for engineers for decades. My interest was first mainly in roads, and later expanded to include railways.

If you're talking from the point of view of a particular road or rail route (e.g. if it's your responsibility to build or maintain that route), then any (road, rail, canal or any other) bridge over that route is an overbridge, and any bridge under that route is an underbridge.

In one case when I was reading about a new road scheme that included new rail and other bridges, the document used the terms "overline bridge" and "underline bridge" for bridges over and under the railway, whether or not involving the main new road, and "overbridge" and "underbridge" for briges over and under the main new road not involving the railway.

 

[61653 HTAFC]

From a railway viewpoint. Overbridge carries something over the railway; underline being the opposite. Hence often in the literature about loco restrictions, it would often mention weak underline bridges, ie the railway being on the bridge bit.

Ellis’ railway encyclopaedia defines “underbridge“ as a bridge allowing passage beneath the railway, and “overbridge” allowing passage over the railway, then cross references to “underline bridge” and “overline bridge“ as the alternative names, but they’re also explained as helping to avoid the confusion caused by highway engineers who use the opposite terminology.

Thanks both. The highway engineers bit suggests that whichever mode is being discussed, the label applied to a crossing refers to how the crossing interfaces with the right-of-way, rather than the other way round.

The hard part will be remembering which way round they go!

 

[Sean Emmett]

In the Network Rail schedule of structures, bridges over the railway are indeed overbridges, and bridges under the railway are underbridges.

So I concur, always consider it from the railway's point of view.

 

[swt_passenger]

Then there’s railway over railway bridges. Overbridge for one and underbridge for the other, or is it correctly an “intersection bridge”?

 

[adrock1976]

In the Network Rail schedule of structures, bridges over the railway are indeed overbridges, and bridges under the railway are underbridges.

So I concur, always consider it from the railway's point of view.

When I have walked underneath a railway bridge, the reference plate has the letters UB followed by the number (also the original railway company that constructed the line such as OWW - Oxford, Worcester, & Wolverhampton). Likewise when I have walked along a bridge over the railway, the reference plate has the letters OB.

When I was at primary school many years ago, I was taught that you bridge over and tunnel under (in normal terms), but I am digressing here.

 

[XAM2175]

(also the original railway company that constructed the line such as OWW - Oxford, Worcester, & Wolverhampton)

This is the Engineer's Line Reference, not a deliberate reference to the original company.

 

[pdeaves]

Overbridge = goes over the railway
Underbridge = goes under the railway

Of course, from the road (or canal, or whatever else) perspective, a railway underbridge is their overbridge!

 

[xotGD]

So when does a very wide bridge become a very short tunnel?

 

[edwin_m]

This is the Engineer's Line Reference, not a deliberate reference to the original company.

ELRs were often chosen to reflect the "working" name of the line, which in the case of OWW was indeed the original company name, but they can be any set of letters as long as they're unique. I believe National Highways also uses ELRs to identify the disused rail structures it is responsible for.

 

[Nottingham59]

So when does a very wide bridge become a very short tunnel?

The simple answer is when the Sectional Appendix says so!

 

[XAM2175]

ELRs were often chosen to reflect the "working" name of the line, which in the case of OWW was indeed the original company name, but they can be any set of letters as long as they're unique.

Yes, I would have been better saying that it is sometimes but not always a reference to the original company, as the primary purpose is to uniquely identify the section of line.

 

[pdeaves]

So when does a very wide bridge become a very short tunnel?

When it's defined as such! Usually, it depends on whether the hole was bored (tunnel) or not (bridge), but that isn't always the case.

 

[Annetts key]

So when does a very wide bridge become a very short tunnel?

It’s definitely a tunnel if in the past staff would get tunnel allowance for walking or working in it!

(The allowance was abolished many, many years ago.)

Often the difference comes down to the reasons behind the construction. You only normally get tunnels where in order to keep the gradient reasonable, the line had to go through the geology and the hill was too high for a cutting.

However, sometimes, it’s required for the railway to be hidden. So rather than it being in a cutting, a “roof” is put on top making it a tunnel.

If the only purpose of the engineering structure is to provide for a path, lane, road, motorway, stream, river, canal or another railway to cross over, then it’s a bridge.

Now the next question is, is it a tunnel or a bridge if you build a shopping centre over the railway?

 

[edwin_m]

It’s definitely a tunnel if in the past staff would get tunnel allowance for walking or working in it!

(The allowance was abolished many, many years ago.)

Often the difference comes down to the reasons behind the construction. You only normally get tunnels where in order to keep the gradient reasonable, the line had to go through the geology and the hill was too high for a cutting.

However, sometimes, it’s required for the railway to be hidden. So rather than it being in a cutting, a “roof” is put on top making it a tunnel.

If the only purpose of the engineering structure is to provide for a path, lane, road, motorway, stream, river, canal or another railway to cross over, then it’s a bridge.

Now the next question is, is it a tunnel or a bridge if you build a shopping centre over the railway?

That's from an engineering point of view. For the operators I believe it becomes a tunnel once it exceeds a certain length.

 

[Ploughman]

Bridge or Tunnel.
If it's Dug through then its a Tunnel.
If its built over then its a Bridge, (Including shopping centres)
The Sectional Appendix has many situations that are arguably wrongly described.
Length is not the main consideration.

 

[swt_passenger]

Bridge or Tunnel.
If it's Dug through then its a Tunnel.
If its built over then its a Bridge, (Including shopping centres)
The Sectional Appendix has many situations that are arguably wrongly described.
Length is not the main consideration.

Isn’t it the case that the sectional appendix is primarily considering safety procedures, not the engineering, so if something built as a bridge needs the same safety procedures to be carried out by traincrew as in a tunnel, it will be described as a tunnel. I think this has been highlighted in previous discussions on this point.