New bridge dimensions

[Ironside]

When looking at replacing level crossings with bridges I understand that one of the problems is the amount of land required for the ramp part of the bridge.

Whilst each level crossing has its own challenges, can anybody tell me roughly how long the bridge would have to be to cross a two track railway. I am particularly interested in the length of the ramp either side of the track.

 

[The Ham]

When looking at replacing level crossings with bridges I understand that one of the problems is the amount of land required for the ramp part of the bridge.

Whilst each level crossing has its own challenges, can anybody tell me roughly how long the bridge would have to be to cross a two track railway. I am particularly interested in the length of the ramp either side of the track.

Roads can not be any steeper than 1 in 10, however it is more normal for them to run at less than 1 in 21 so as to not need to provide an alternative route for wheel chair users.

What also needs bearing in mind is that the bridge deck of a road is at least 1m thick, so you need to allow for this in addition to the clearance under the bridge.

Therefore if you build a bridge with 4m of clearance the ramps are likely to be at least 105m long.

The width of the carriageway is likely to be 5.5m wide for a road with low numbers of HGV's, 6.1m wide for bus routes and 7.3m wide for roads with a lot of HGV's. Add to that a further 2m to 4m either side for footways and/or cycleways.

Any earth banks are likely to have a slope of 1 in 2 making them add a further 0-10m on width of the land needed for the road.

The actual span of the bridge deck is less complicated, as long as it crosses the railway at nearly 90 degrees, so only needs to be as wide as gap between the existing barriers.

All in all there will be a lot of land take to provide a bridge, although if the railway can be lowered by even just 0.5m it can make significant difference to the size and scale of the bridge.

 

[swt_passenger]

It's quite a massive undertaking at a crossing in a rural area, but even if the amount of work seen at a closed crossing such as Banbury Rd on the WCML is able to be fitted in, like this:

http://goo.gl/maps/AhyUO

...nobody seems to have come up with an explanation how you fit these massive ramps into the typical urban streetscape...

Try building that in Kingston or Richmond...

 

[Eagle]

...nobody seems to have come up with an explanation how you fit these massive ramps into the typical urban streetscape...

It can be done (Tile Hill station, crossing closed circa 2004).

 

[swt_passenger]

It can be done (Tile Hill station, crossing closed circa 2004).

I'm thinking of where there are shops, houses etc on both sides of the road right up against the railway though. It doesn't look like they did much demolition of property at Tile Hill?

This sort of thing: http://goo.gl/maps/ANm34

 

[Eagle]

This sort of thing: http://goo.gl/maps/ANm34

In that case the only real solution would be to block off the road and divert through traffic (via Pope's Grove in this case which isn't too far) and pedestrians could use the station footbridge*. Which is exactly what happened at the next level crossing along from Tile Hill, namely Canley.

*Although that might become a problem if Strawberry Hill ever gets barriers.

 

[Ironside]

Wow that is a lot of land take. I see also that some of these new bridges snake over to one side. I guess this is to get the slope shallow enough without to much linear length, whilst also allowing the level crossing to continue being used while the bridge is being used.

 

[Ploughman]

Roads can not be any steeper than 1 in 10, however it is more normal for them to run at less than 1 in 21 so as to not need to provide an alternative route for wheel chair users.

What also needs bearing in mind is that the bridge deck of a road is at least 1m thick, so you need to allow for this in addition to the clearance under the bridge.

Therefore if you build a bridge with 4m of clearance the ramps are likely to be at least 105m long.

The width of the carriageway is likely to be 5.5m wide for a road with low numbers of HGV's, 6.1m wide for bus routes and 7.3m wide for roads with a lot of HGV's. Add to that a further 2m to 4m either side for footways and/or cycleways.

Any earth banks are likely to have a slope of 1 in 2 making them add a further 0-10m on width of the land needed for the road.

The actual span of the bridge deck is less complicated, as long as it crosses the railway at nearly 90 degrees, so only needs to be as wide as gap between the existing barriers.

All in all there will be a lot of land take to provide a bridge, although if the railway can be lowered by even just 0.5m it can make significant difference to the size and scale of the bridge.

The only problem with that is that OHLE clearance will be required on all new structures.
I believe that to be in the order of 5.5m

 

[jopsuk]

the clearance under OHL is 5.5m. Ideally, new bridges get built so that either the existing OHL is not modified, or any future OHL can be simple plain line OHL, not lowered/fixed to the structure.

 

[LE Greys]

The A10 bridge at Foxton (which has been in the news the last couple of months) would most likely involve a complete bypass around the village, and hopefully be made wide enough for a potential second carriageway if it's ever needed. I'm not sure whether the crossing would remain open for local traffic, the article doesn't say, but it might be a bit of a pain in the backside to do this. In other locations such as Helpston, it might be worth having one bridge to replace two or three crossings, positioned between two existing ones and running the ramps alongside the line, although that would require four ramps instead of two.

 

[jopsuk]

I'd hope a crossing will be retained at Foxton- though I could see it being converted to CCTV operation. At the very least a foot and cycle crossing needs to be retained, as to not cut the north part of the village off, and because the bypass will likely be an unutterably hostile place for cyclists - there's a new cycling campaign been formed to lobby for better facilities along the A10 corridor between Cambridge and Royston.

 

[LE Greys]

I'd hope a crossing will be retained at Foxton- though I could see it being converted to CCTV operation. At the very least a foot and cycle crossing needs to be retained, as to not cut the north part of the village off, and because the bypass will likely be an unutterably hostile place for cyclists - there's a new cycling campaign been formed to lobby for better facilities along the A10 corridor between Cambridge and Royston.

IIRC, they are planning to have a public footbridge, probably also for passenger use.

 

[Bald Rick]

If Network Rail is contributing to the cost of the bridge, then the crossing must go. Besides the Foxton 'bypass' has only been thought about for the last 60 years.

Good news about Kings Dyke though, long overdue.

 

[The Ham]

The only problem with that is that OHLE clearance will be required on all new structures.
I believe that to be in the order of 5.5m

the clearance under OHL is 5.5m. Ideally, new bridges get built so that either the existing OHL is not modified, or any future OHL can be simple plain line OHL, not lowered/fixed to the structure.

I couldn't remember the clearance required, so just gave an example of 4m of clearance, if it is going to be closer to 6.5m than that, plus 1m from the bridge deck, means ramps of about 155m.
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I'd hope a crossing will be retained at Foxton- though I could see it being converted to CCTV operation. At the very least a foot and cycle crossing needs to be retained, as to not cut the north part of the village off, and because the bypass will likely be an unutterably hostile place for cyclists - there's a new cycling campaign been formed to lobby for better facilities along the A10 corridor between Cambridge and Royston.

A pedestrian and cycle bridge is a lot easier to build as the ramps can zig-zag and have a much smaller footprint. Also as the bridge is only a total of up to 4m wide and the loads being carried are a lot lower it is normal for the ramps to be self supporting (i.e. no earth banks) which further reduces the footprint of the bridge.