Bridge or tunnel?

[meldrum]

A chap I know who works for Network Rail told me that a while ago he was working on the WCML at Preston Brook a few miles south of Warrington. Here is 'Preston Brook Tunnel' which he states has a sign attched with the tunnel name, the 'structure number' in this case 48 and the length, 61 meters. So the question is, can this really be a proper tunnel being so short and can a bridge ever be a tunnel? Also out of interest what is the networks shortest tunnel?

[60129 GUY MANNERING]

I think from memory Askham Tunnel on the ECML near Retford is only 58 yards long.

[Mickey]

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[52A]

Peak Forest 29 yds!

[StevieG]

I seem to recall chat with civil engineer / P.Way types about this on occasion over many years, and a rule of thumb for when a bridge became a tunnel was thought to be 50 yards, though none of these could direct me to it in writing. (Which camp a structure exactly 50 yards long fell into, I'm now unsure).

However, I now doubt that any such definition is applied consistently. A 29-yard tunnel has just been quoted, and where the railway has been bridged in modern times for modern road/motorway building, some structures definitely look to be more than 50 yards wide (along the railway; while still looking like a bridge though - some quite high indeed).
Where 'rafts' have been newly-built over the line between retaining walls or cutting sides, specifically to enable buildings to be erected above (e.g. outside Liverpool Street, south and north of Primrose Street, and east of Ilford station), the railway has been enclosed but they don't appear in 'the Appendix' and wouldn't surpise me if more likely to be listed amongst bridges in infrastructure data.

[third-rail]

I seem to recall chat with civil engineer / P.Way types about this on occasion over many years, and a rule of thumb for when a bridge became a tunnel was thought to be 50 yards, though none of these could direct me to it in writing. (Which camp a structure exactly 50 yards long fell into, I'm now unsure).

However, I now doubt that any such definition is applied consistently. A 29-yard tunnel has just been quoted, and where the railway has been bridged in modern times for modern road/motorway building, some structures definitely look to be more than 50 yards wide (along the railway; while still looking like a bridge though - some quite high indeed).
Where 'rafts' have been newly-built over the line between retaining walls or cutting sides, specifically to enable buildings to be erected above (e.g. outside Liverpool Street, south and north of Primrose Street, and east of Ilford station), the railway has been enclosed but they don't appear in 'the Appendix' and wouldn't surpise me if more likely to be listed amongst bridges in infrastructure data.

add to this, cut and cover has to be a bridge,a tunnel has to dug through virgin ground.

a by question when does a bridge become a viaduct?

[PinzaC55]

add to this, cut and cover has to be a bridge,a tunnel has to dug through virgin ground.

a by question when does a bridge become a viaduct?

Sunderland North Tunnel was built by cut and cover but it is still a tunnel.

The North Eastern Railway only ever referred to "Bridges" not "Viaducts" so although the Royal Border Bridge is obviously a viaduct to the layman it is still a Bridge. I think even the mighty Belah viaduct was still a bridge as far as the NER was concerned.

[Bryan]

Structures to be treated as tunnels in relation to the rules are those listed as such in the Sectional Appendix. Regardless of length, name or construction.

The length bit comes in for bridge inspection by the Civil Engineer, structures under 2 chains in length usually bridges (exact length may differ over time and between different railway companies) are inspected as one item. Longer structures are inspected in sections, most structures inspected this way are tunnels, so for inspection if it is over 2 chains long it is a 'tunnel'.

For strict engineering useage if it is dug through something it is a tunnel, if it is built over something it is a bridge, and if you build a structure then bury it you have a covered way.

[Mickey]

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[meldrum]

Many thanks for all your responses.

[StevieG]

Slightly off topic but this reminds me of the more 'modern interpretation' of what is a railway junction?.

For example 4-straight running lines with a set of crossovers or a ladder crossing can how days be called a Junction like a place called 'Radlet Junction' on the 4-track Midland main line out of st Pancras to my knowledge going back to the early 1970s it was only 4-straight roads through Radlet?.

A Junction to me is usually (but not always) a main route with a branch route leading off of it away from the main route.

At least 'Radlett' is a several crossovers location (six? ; Making all four running moves catered for?).
When the DF-DS and US-UF crossovers of 1970s-on at Hatfield, sited in the little bit of straight between opposite curves about 1/4-mile south of the station, were done away with (following the broken rail derailment disaster I think), a new US-UF 70mph crossover was put in about halfway between Redhall and Marshmoor (old box sites) where there had been only four straight(literally) tracks.
This is officially named 'Marshmoor Junction'.

[Mickey]

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[Trestrol]

Isn't it a bridge becomes a tunnel when it is longer than the width of the tunnel mouth? I am sure i heard that on the radio.

[Mickey]

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[PaulG]

According to British Rail GEOGIS Users Guide for 1992:

"A bridge is a structure of any dimensions that enables a railway or road or watercourse to pass over or under another railway or road or watercourse. Normally, its length will be less than 50m. If greater than 50m it will usually be entered as a tunnel.

A bridge span of less than 2m will be defined as a culvert
A bridge span of less than 0.9m will be a pipe.
A bridge of 5 spans or more will be defined as a viaduct."

Regards
Paul