Tuesday, April 6, 2021

1896 (Amtrak+MNCW)/New Haven Walk Bridge over Norwalk River

(Bridge Hunter; no Historic Bridges; HAER; 3D Satellite)

MNCW = Metro-North Commuter Railroad

The bridge carries approximately 175 trains and 125,000 passengers a day. 

HAER CONN,5-NEWHA,37--29
29. Norwalk River Bridge. Norwalk, Fairfield Co., CT. Sec. 9108, MP 41.47. - Northeast Railroad Corridor, Amtrak Route between New York/Connecticut & Connecticut/Rhode Island State Lines, New Haven, New Haven County, CT

I also wanted a shot that captures how tall the high-tension towers are on either side of the bridge.
HAER CONN,5-NEWHA,37--25

The HAER photos gave me deja vu. Then I realized this is the same railroad that built the Cos Cob power plant. That plant is next to a rolling bridge.

I captured a satellite image because this bridge should already have been replaced. It was fine at 100 years old, but since 2014 it has been having a lot of breakdowns.
3D Satellite

Now I normally would pass up yet another swing bridge, but this one caught my eye with its heavy-duty deck truss. Then I noticed it has four tracks and it reminds me of a lattice truss. Bridge Hunter calls it a double-intersection Warren truss. This is now the third 4-track swing bridge that I have found in the USA. But this is the only one that is currently standing. But not for long. The other two bridges were in Conneaut, OH, and NYC.

I count at least six workers on the fixed span and one riding the swing span. It appears the workers are not needed for the electrical connections but for the unlocking and locking of the rails. The new bridge should automate that.
Photo via Bridge Hunter via TheHarlemLine, License: Creative Commons Attribution-Share-Alike (CC BY-SA)

The comment on this video says this is the last 4-track swing bridge in the world.
(new window) To skip the railfan part, go to 1:44. To skip the parade of sailboats, go to 8:08. There were at least four workers riding the moving span and eleven on the east span. Or did a bunch of white hats (management) come out for the show? I noticed the span started moving before the warning buzzer was sounded. Tools of the trade: prybars and sledge hammers.
The railfan part was interesting in terms of how slow the passenger trains were going. I could not find the planned speed limit for the new bridge.

I was able to spot 13 workers in this view. At what height does OSHA want harnesses for workers standing on the edge of a steel structure?
2:27

This is the post that introduced me to this massive swing truss and turntable.
(new window) (source) This video shows that it can be opened with fewer workers. It also demonstrates that noise is supposed to be made before the span moves. In this case, while the span moves. And even longer because I think he forgot to turn off the bell after it opened. Around 4:00 I was reminded that the east coast uses tugboats instead of towboats.

It not only has a heavy-duty truss, it has cut-stone abutments.
Street View

I saw a figure of $400m and some for the cost of a replacement. Then in the following image source I saw $510m with the start of construction at the end of 2019 and completion in 2024. However, I could not find a date for that reference. Now construction is supposed to start in 2021 and take 5-6 years to complete.
railway-technology, Credit: Walk Bridge Program
"The new bridge will be a 240ft vertical lift structure, with a minimum horizontal navigational clearance of 200ft and a vertical clearance of 60ft when the span is raised completely. The total length of the bridge will be 690ft."

The current web page avoids providing an estimated cost figure by saying the costs are currently being updated. However, I did find: "A federal judge has cleared the way for state and federal transportation officials to move forward with a $1.1 billion project to replace a 122-year-old movable railroad bridge in Norwalk." [NorwichBulletin] It should be noted that the project includes work in addition to replacing the bridge such as repairing a railroad embankment.

The design is what I would expect --- a lift bridge where the towers and their foundations are built around the old bridge. And it uses two independent 2-track spans. This allows maintenance to be done on one span while the other still carries trains. It also allows the old bridge to be replaced two tracks at a time. Train service should be impacted for only two weekends. [alternatives]
Fact Sheet

Unfortunately, their comparison of design alternatives don't provide cost figures for the movable designs. So when they say it would cost $425m-$475m to rehabilitate the existing structure, I don't know what the comparable cost is for the 240' lift design. It won't be $1,100m because I assume that figure covers the project adders. And those adders remain constant independent of bridge design. They considered two low-level fixed bridge designs. It sounds like the first one was a steel girder design for $290m-$340. The other was a through truss design for $360m-$390m that had a 170' span with 26' clearance. "The elimination of movable bridge elements such as lift span towers, mechanical equipment, electrical equipment and utilities result in an approximately 15% cost savings." 26' is not only too low for rich men and their sailboats, it would not allow dredging equipment to get upstream past the bridge.  [alternatives]




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