06-03-2010, 07:18 AM
Herc,
A ballasted deck will allow the right of way over the bridge to be maintained with the same equipment used to maintain non-bridged right of way, and I suspect it spreads the load over the bridge better than a non-ballasted bridge. And as Doctor Wayne commented, alignment is more flexible than rail-on-bridge-tie. The latter also complicates the maintenance of the right of way approaching the bridge as it must meet the bridge height - adding too much ballast to the approaches, for example, would cause a problem when you get to the bridge. Ballasted decks don't have that problem (I've seen some with a LOT of ballast on them!)
As to why they do it in some cases, and not in others, I don't know. I would suspect expense, expected bridge load and when the bridge was designed are a couple factors. For example, the ballasted decks around here are generally shorter spans, more recently built (maybe 1930 on) and on heavy main lines. Recent grade crossing elimination projects in my area have all been ballasted deck.
Matt
A ballasted deck will allow the right of way over the bridge to be maintained with the same equipment used to maintain non-bridged right of way, and I suspect it spreads the load over the bridge better than a non-ballasted bridge. And as Doctor Wayne commented, alignment is more flexible than rail-on-bridge-tie. The latter also complicates the maintenance of the right of way approaching the bridge as it must meet the bridge height - adding too much ballast to the approaches, for example, would cause a problem when you get to the bridge. Ballasted decks don't have that problem (I've seen some with a LOT of ballast on them!)
As to why they do it in some cases, and not in others, I don't know. I would suspect expense, expected bridge load and when the bridge was designed are a couple factors. For example, the ballasted decks around here are generally shorter spans, more recently built (maybe 1930 on) and on heavy main lines. Recent grade crossing elimination projects in my area have all been ballasted deck.
Matt
Matt Goodman
Columbus, Ohio
Columbus, Ohio