When/where does track have ballast on bridge or trestle?

[rogergperkins]

I have install Atlas code 65 True-Track on part of the mainline of my layout; formerly had Kato Unitrack and used two single track trestles.
Now I am attempting to find an appropriate style "bridge" for that area which would allow for use of the standard True-Track.
I live in Peoria, IL and have driven north along the Illinois River and the railroad on the west bank.  I see several areas where small "bridges" appear to support ballasted track.  Thanks in advance.

[rogergperkins]

I have found references to "ballasted decks" and some photos.  When I search for models in n-scale, I find Micro-Engineering has some similar models, however based on a limited search of dealers, no one has them in stork. 

[DKS]

Some eBay sellers have the Micro Engineering ballasted deck bridges--

http://www.ebay.com/itm/Micro-Engineering-N-80041-Concrete-Bridge-Deck-pkg-2-/230521478181?pt=Model_RR_Trains&hash=item35ac269c25

You can also turn an open deck bridge into a ballasted deck by simply making a solid deck from sheet styrene, with raised edges made from square strip stock. The advantage of making it yourself is the deck can be fabricated to exactly fit the track you're using.

There are no rules I'm aware of regarding when or where ballasted deck bridges are used, except that they're usually plate girder type, either deck or through.

Here's a through plate girder ballasted deck bridge in West Trenton, NJ, where I used to live:

[rogergperkins]

David, your reply is 100% on target! Thanks.
My plan is to use the True-Track sections to span the stream which required two Kato trestles thus is about 19+ inches.
I need to find the applicable side parts.
Amazing that I cannot find a photo of the 80041, but I do find it for sale by some e-tailers.

[randgust]

The rule isn't specifically for ballasted vs. non-ballasted bridges.  The rule is for track geometry and how you keep it there.   A 'standard' bridge with bridge ties directly on the steel stringer can't be adjusted for geometry; about the only thing that can happen is that the bridge ties rot out and have to be replaced.   That can be a true bear on a bridge.   Most have speed restructions of some kind.   Your 'impact loads' are transmitted to load-bearing members as well (think flat wheels, that kind of thing).

If you're on a main line that is normally maintained for FRA Class III (40mph) or above, the track geometry, run-out, superelevation, vertical changes, etc. start to get a lot tougher.  If the track is ballasted, you can adjust that geometry, change out individual ties as-needed.   There are virtually no speed restrictions on a ballasted deck compared to regular track.  My favorite is (of course) the Canyon Diablo cantilever truss in Arizona that is set for 90mph - fully ballasted.   And, the ballast helps spread out the impact loads, too.

Remember that the bridges have to be designed to carry the dead weight of the ballast in addition to the normal weight plus the live load and impacts.  So you don't see wimpy designs or light pin-connected trusses with ballasted decks.  Normally girder bridges, concrete spans, some deck trusses but ballasted through trusses are a bit rare.

To really simplify, for modeling purposes, if you're not running a high-speed passenger or freight operation, heavy tonnage, etc., you can probably go either way.  It's a real signature though of a heavy, high-speed line to have ballasted deck bridges.  What you'll almost never see is a ballasted deck on slow-speed branches, logging & industrial railroads, etc.

[rickb773]

Evergreen Ave. overpass in Woodbury, NJ. Formerly Pennsylvania-Reading Seashore Lines, now Conrail Shared Assets:

[Catt]

Ballasted deck trestle Saranac, MI.The under growth is so thick that in the summertime you can walk accross this trestle and not even realize your on a trestle.

[rogergperkins]

Thanks to all for the photos.  It appears there are various options that with some licenses would have a prototype.

This is the area and trestle I am replacing; it looks fine, but now this section is True-Track single main versus the Kato Unitrack.
This trestle represents the one on the B&O branch line where it crossed the Kaskaskia River between Beecher City and Cowden, IL; line now does not exist.


This is from the B&O branch line which spanned the Kaskaskia River between Beecher and Cowden, IL; however, I do not
think it was a ballasted deck.
I could cannibalize the old Atlas arched stone bridge supports to simulate this design.

[Zox]

There are no rules I'm aware of regarding when or where ballasted deck bridges are used, except that they're usually plate girder type, either deck or through.

Or not...

[DKS]

Or not...

Um... that's a viaduct. (Yes, technically a bridge, but quite a different thing from what we were discussing.)

[jmlaboda]

In a big way it depends on two things... when the bridtge or trestle was built and now heavy is the line used.  Newer bridges are ballasted with a layer of steel and concrete being under the track while older bridges and trestles were not, largely because most roads preferred to fill these in as thy were able.  A lot of raillines where large fills are found for the track to pass over were originally tall trestles that were built when the line was built and with time they were filled in with dirt and rip-rap (large stone) over a number of years since this would allow the track to be upgraded for higher speeds and heavier equipment.

The viaduct shown in the previous post were major undertakings done by some roads and were intended to span a number of decades without a lot of maintenance and repair... typically with a famous civil engineer involved with the road's construction.  Elsewhere deck girder bridges were used, mostly without a top layer of ballast while newer through girder bridges (built from roughly 1950 on, especially if involved as a part of the construction of a major highway or interstate) ballasted decks were common, in part because it was money from government that helped pay for it.

[Zox]

Um... that's a viaduct. (Yes, technically a bridge, but quite a different thing from what we were discussing.)

  It's a bridge, with a ballasted deck. And when I read this:

My plan is to use the True-Track sections to span the stream which required two Kato trestles thus is about 19+ inches.

...I didn't figure he was going for a single span of 19 inches, so it's going to be a "viaduct" of some form in any case.

What did I miss?

[DKS]

It's a bridge, with a ballasted deck. And when I read this:

...I didn't figure he was going for a single span of 19 inches, so it's going to be a "viaduct" of some form in any case.

What did I miss?

You win, you win.

[havingfuntoo]

Randgust has the answer, high speed track needs to be ballasted so that the track can be kept aligned and at the correct elevation, it also enables distribution of the weight more evenly over the structure.

[up1950s]

That Amtrak wreck in Louisiana was on a high speed track and the bridge wasn't ballasted IIRC .