Grade separation - height difference?

[Alexj16180]

When I'm looking out the window and see a pair of tracks peel off, climb up and over on a bridge (or under), I'm always surprised by how quickly the height difference appears. I know minimum bridge clearance but not how thick the track bed would be on a bridge + the bridge itself - does anyone know what the vertical difference would be rail to rail? And on that subject, which junction has the shortest distance from level tracks to grade separation?

 

[brad465]

I'm not an expert, but minimum clearance will vary considerably based on a number of factors, most notably the presence of overhead wires, the loading gauge of the route (higher gauges like W12 need more clearance than W6A for example) and linespeed would also likely be involved - higher linespeeds presumably need stronger foundations, so bridges would be thicker and thus raise the track bed higher.

 

[Snow1964]

The bridge deck will vary depending on the span, how skew it is, and age and type of bridge.

Could be as little as 0.4m from underside of bridge to top of rails, but 0.6 - 0.7m would be more typical.

No idea which is shortest ramp, but flyover at Twickenham is quite steep (a remnant of when station was other side of road, before it was rebuilt (station relocation, started before WW2, finished in 1950s)

 

[swt_passenger]

I'm not an expert, but minimum clearance will vary considerably based on a number of factors, most notably the presence of overhead wires, the loading gauge of the route (higher gauges like W12 need more clearance than W6A for example) and linespeed would also likely be involved - higher linespeeds presumably need stronger foundations, so bridges would be thicker and thus raise the track bed higher.

W10 and W12 are the same height, and are actually a few cm lower than W6A at the vehicle centre line, so it needs the same vertical height, but over the entire width. Then there’s also the dynamic envelope for the top/outer corners, so it needs flat bridge decks rather than arches, but if the grade separated flyover in question is already a typical girder bridge it won’t need to be raised, even if it needs widening.

 

[Bald Rick]

typically 7 metres. A little less for anything not built in the last 40 years.

 

[norbitonflyer]

No idea which is shortest ramp, but flyover at Twickenham is quite steep (a remnant of when station was other side of road, before it was rebuilt (station relocation, started before WW2, finished in 1950s)

It is also a descending gradient, which may allow a steeper gradient. Some of the shortest will be on the London Underground, where, of course, the height difference can be less.
The shortest ramps will probably in a situation where both the main and diverging route are on gradients

 

[AM9]

It is also a descendibg gradient, which may allow a steeper gradient. Some of the shortest will be on the London Underground, where, of course, the height difference can be less.
The shirtest ramps will probaly in a situation where both the main and diverging route are on gradients

Yes, that's my experience, often the under route is on a falling gradient either reducing the gradient of the over route or shortening its length, e.g. the GEML Ilford flyover.

 

[furnessvale]

It is also a descendibg gradient, which may allow a steeper gradient. Some of the shortest will be on the London Underground, where, of course, the height difference can be less.
The shirtest ramps will probaly in a situation where both the main and diverging route are on gradients

Hazel Grove Chord is a good example of creative use of different gradients on the diverging lines to maximise effect in the shortest distance.