Minimum height of a railway flyover?

[Nottingham59]

If a flat rail junction is to be replaced by a flyover, say at Newark flat crossing, then how high does that flyover have to be?

Obviously, it will need to accommodate W12 gauge rolling stock on the lower track, plus an allowance for electrification. Add the depth of the upper beam supporting the upper track, plus any slab or ballast and the upper rail itself. What is the minimum needed, measured vertically from railhead to railhead?

 

[D1511]

It would depend entirely on the design of the overhead structure, which could be a range of depths, depending on loading, spacing between supports, materials, reinforcement etc..
A more standard measure would be from the railhead to the underside of the overhead structure, and EWR are designing to 5.8m, although you can get as tight as 4.5m with special OLE

 

[Zomboid]

Contact wire height ranges between 4.2 and about 6m, and the required height at a given location will depend on things like where level crossings are and the line speed (this being the whole conundrum at Steventon).

But you'd probably want the bottom of the deck to be at least 5m. Don't know how deep bridges tend to be from deck base to railhead, but I think that's probably quite variable. Call it 1m and you're probably safe, so 6m is my guess.

 

[HSTEd]

As an example of how variable the depth of a bridge deck can be, the now Metrolink bridge over the M60 on the Bury line (near Besses O' Th' Barn tram stop) has an inverted T-beam design, where the "fin" is between the two running lines, to reduce the height of the rail level above the ground.

 

[Bald Rick]

Rail to rail, allow 6-7m depending on local circumstances.

 

[The Pelican]

Electrified or Metro lines can generally accomodate much steeper gradients, although most of the LSWR grade seperations, such as at Raynes Park, New Malden and Battlesdown west of Basingstoke, preceded electrification.

 

[GingerSte]

5100mm running edge of rail (below) to soffit (underside) of structure. Allows for OHLE and standard clearances. Also allows for up to W12.

Do not use this info in a design without confirming it for yourself. I ain't taking any design liability!

 

[zwk500]

If a flat rail junction is to be replaced by a flyover, say at Newark flat crossing, then how high does that flyover have to be?

Obviously, it will need to accommodate W12 gauge rolling stock on the lower track, plus an allowance for electrification. Add the depth of the upper beam supporting the upper track, plus any slab or ballast and the upper rail itself. What is the minimum needed, measured vertically from railhead to railhead?

Here's a to-scale engineering drawing of the concrete box flyover at Mirfield: https://sacuksprodnrdigital0001.blob.core.windows.net/twao-huddersfield-westtown/Huddersfield to Westtown (Dewsbury)/02 TWAO Application Documents/NR13 Planning Drawing - Flyover (RBA 1) - Proposed Elevation Cross Section.pdf

just under 5m (4.978m, to be exact) is allowed for clearance from lower rail to underside of the bridge, and you can see the canted tracks are sitting on a decent thickness of ballast above that. If you download the file I think Acrobat Reader lets you measure scaled distances.

The lines being carried above at this location are intended mainly for fast passenger trains, and are crossing at quite a thin angle on a curve, so the design of a flyover for Newark (lower speed, heavier freight, straighter alignment and wider angle) might vary a bit, but it's a decent approximation for a modern structure designed to go above an electrified W12 profile.

 

[Bayum]

Which would be more cost effective? A cut under or a bridge?

 

[zwk500]

Which would be more cost effective? A cut under or a bridge?

Depends on the site. At Newark, given the proximity of the river Trent and A46 flyover, I suspect neither line could be lowered. However at Werrington jn near Peterborough, a dive-under was built.

 

[edwin_m]

Which would be more cost effective? A cut under or a bridge?

Other things being equal, building up would be cheaper. Any existing infrastructure could be built above without changing it up, whereas digging beneath an existing line will inevitably disrupt it. However, there are many reasons why other things may not be equal, such as ...

Depends on the site. At Newark, given the proximity of the river Trent and A46 flyover, I suspect neither line could be lowered. However at Werrington jn near Peterborough, a dive-under was built.

... Werrington was probably down (!) to the A15 which crosses the Spalding line a short distance to the east. Lowering the A15 to pass under new elevated tracks would have clashed with the existing tracks at grade-ish, needing them to be elevated as well.

 

[zwk500]

Werrington was probably down (!) to the A15 which crosses the Spalding line a short distance to the east. Lowering the A15 to pass under new elevated tracks would have clashed with the existing tracks at grade-ish, needing them to be elevated as well.

IIRC there were outline designs for both a flyover and dive-under produced, and a public consultation run to gauge support for each option. It might take a bit of digging to find the flyover designs online though!