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[Brian556]

I have never seen anything like this and can't even tell what he heck is going on
https://www.google.com/maps/@30.0694818,-90.3917535,3a,15y,143.64h,89.16t/data=!3m7!1e1!3m5!1sQtAS2R69c0i2VBw-1Iv71w!2e0!6s%2F%2Fgeo2.ggpht.com%2Fcbk%3Fpanoid%3DQtAS2R69c0i2VBw-1Iv71w%26output%3Dthumbnail%26cb_client%3Dmaps_sv.tactile.gps%26thumb%3D2%26w%3D203%26h%3D100%26yaw%3D310.89233%26pitch%3D0%26thumbfov%3D100!7i16384!8i8192

[SteveG1988]

Spreading the weight out along a truss to allow for replacement of large sections of the trestle?

[sparker]

Spreading the weight out along a truss to allow for replacement of large sections of the trestle?

That's CN trackage, former Illinois Central; Amtrak uses it for their Chicago-N.O. service.  The viaduct structure is a standard box girder type, configured so the tracks ride over the top of the girders rather than through them in order to take advantage of the weight-bearing characteristics of I-shaped girders.  In this waterlogged location, girders and the hardware securing them tend to rust out over a short time; what you're probably looking at in this picture is a temporary deck-truss bridge being placed where a girder section was/is to be removed.  A permanent bridge section will be constructed offsite and then put into place; the truss is simply a stopgap to keep rail traffic moving in the interim.

[SteveG1988]

Yeah i just drove by it twice today, it is definitely a weird way to do it first time you see it, but it makes sense when there is no really firm dry land to build your new concrete girder bridge on.

[M3100]

Here is a picture of the bridge construction from a rainy summer afternoon in 2019; that area is the Bonnet Carre Spillway.  The Army Corps of Engineers opens it up as needed to release water from the Mississippi River into Lake Pontchartrain to reduce the risk of downriver flooding.  IIRC the rail line is closed to Amtrak's City of New Orleans and CN freights for some duration while the spillway is open.



On another note - it was interesting to see how much of I-10 is built as an elevated freeway, both over water and land.  Many more bridges, and less earthmoving, than in arid California.

[MCRoads]

[...]
On another note - it was interesting to see how much of I-10 is built as an elevated freeway, both over water and land.  Many more bridges, and less earthmoving, than in arid California.

I have been on I-10 in LA, and it is amazing how long they are. They are among the longest bridge structures in the world, actually. If you drive on I-310, from the start of the elevated portion, to the end on I-59, you would go approximately 30 miles, which is a bit longer than the Lake Pmnchatrain Causeway.
My mom got anxious driving them, as they are so remote. She always stopped to get gas before the bridge, easier going East because of Lafayette.

[sparker]

[...]
On another note - it was interesting to see how much of I-10 is built as an elevated freeway, both over water and land.  Many more bridges, and less earthmoving, than in arid California.

I have been on I-10 in LA, and it is amazing how long they are. They are among the longest bridge structures in the world, actually. If you drive on I-310, from the start of the elevated portion, to the end on I-59, you would go approximately 30 miles, which is a bit longer than the Lake Pmnchatrain Causeway.
My mom got anxious driving them, as they are so remote. She always stopped to get gas before the bridge, easier going East because of Lafayette.

I think you meant to say I-55 rather than 59, which is part of the same continuous bridge structure centered around I-10 west of metro NOLA.  You'll hit surface alignment on either I-10 or the I-55/12 combination before even getting near the south end of I-59 near Slidell. 

[MCRoads]

[...]
On another note - it was interesting to see how much of I-10 is built as an elevated freeway, both over water and land.  Many more bridges, and less earthmoving, than in arid California.

I have been on I-10 in LA, and it is amazing how long they are. They are among the longest bridge structures in the world, actually. If you drive on I-310, from the start of the elevated portion, to the end on I-59, you would go approximately 30 miles, which is a bit longer than the Lake Pmnchatrain Causeway.
My mom got anxious driving them, as they are so remote. She always stopped to get gas before the bridge, easier going East because of Lafayette.

I think you meant to say I-55 rather than 59, which is part of the same continuous bridge structure centered around I-10 west of metro NOLA.  You'll hit surface alignment on either I-10 or the I-55/12 combination before even getting near the south end of I-59 near Slidell. 

Well, that’s the second rout I’ve screwed up this week... oh well.

[froggie]

Combined length of viaduct from I-310 south of US 61, via I-10, to I-55 south of Ponchatoula is a little over 38 miles.  22 miles of that is on I-55 alone.  The old non-elevated alignment of US 51 is still driveable, adjacent to the I-55 segment.

[seicer]

It looks like the crossing is being replaced with an overhead gantry crane that's mounted on tracks: https://goo.gl/maps/B7MpjjHPvMNVKSPv9

• 17-0244, Illinois Central Railroad (ICRR) proposes to replace their rail bridge across the Bonnet Carre Spillway near Norco, St. Charles Parish, Louisiana: "ICRR proposes to replace an existing timber and concrete railroad bridge with a new concrete railroad bridge across the Bonnet Carre Spillway near the southwest shore of Lake Pontchartrain.  The bridge would be approximately 11,000-feet long and would be constructed 50 feet north of the existing timber trestle bridge with tie-backs into the existing rail alignment near both the upper and lower guide levees of the spillway.  The new bridge would be constructed by track-mounted equipment on the lake side of the existing bridge.  Temporary roads will be constructed with timber mats to the south of the existing railroad alignment to access the equipment staging areas that will be located near the upper and lower guide levees.  The existing timber bridge would be dismantled and removed following construction of the new bridge."
• Review Plan
• Passenger rail is finally making tracks in Louisiana: "The aged bridge, which runs through St. Charles Parish, can accommodate traffic at 10 mph, which has also stalled growing freight traffic on the rail line. With the proposed rail service, a bridge would be needed capable of supporting 80 mph traffic. It would cost $60 million to replace the bridge, which is owned Kansas City Southern."