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[roadman65]

https://goo.gl/maps/CQfSZzAUQX8Xqt3U7
You will see a power lines cross I-78 near Martinsville, NJ in the early 2000s.

https://goo.gl/maps/6oBh9K2KmfWNoN2n7
Now look at most recent. Same location but years later.


It is not only here but in a lot of places utility companies have been removing all truss like assemblies for the mast types.  I don’t mind the look, but why waste monthly customer money if it’s a move to go along with the times.

[Brandon]

It’s usually due to foundation issues.  Either the concrete supports are rotten or the steel is rusted through.

[tolbs17]

Because truss structures are substandard and are aging?

[Mr. Matté]

Your specific example, the line dated back to the 1920s (part of the system of 230 kv lines that extended from the Conowingo Dam in MD, across eastern PA & central NJ, and up to the Scranton area).

[Henry]

This is not limited to just the steel towers either. In the South, there used to be a bunch of wooden poles used as transmission towers, but now they are being replaced by new tubular structures. The most common examples of such would most likely be in NC (and SC, to a certain extent), where it's turned into an ongoing process.

[jeffandnicole]

Because things don't last forever.

Also, it's not a sudden purge, but rather the end result of a few decades of planning.

[Mr_Northside]

As others mentioned, these things get inspected.  If it seems like they're all aging out, they'll need replaced.

Also, sometimes it might be if newer, more reinforced structures are needed if they're upgrading (or expanding) the line.   In the pics you have, it looks like they also went from a single conductor per phase line, to a dual-conductor one, which may have added weight/stress/tension those towers couldn't support (though, based on the age Mr. Matté places them at, they were probably aging out anyway)

[Dirt Roads]

Another more important factor: design lifespan.  Even back in older times, it is likely that the lifespan was specified in the design of the power lines (and most other forms of infrastructure).  Design lifespan becomes a liability issue as any structure gets older than its design requirements, and even worse, if other older structures of same/similar designs begin to show fatigue issues before the age of your particular structure.  There's also a related factor of deferred maintenance, which will reduce the expected lifespan of certain structures.

[lepidopteran]

Two other reasons I've heard.

• Locating the wires above the tree line.  This is important, since a frequent cause of power outages in ice storms is heavy branches falling on the conductors.
• Increased capacity.  Since new power line routes are typically subject to NIMBY opposition, the solution to greater power demands is often to upgrade the existing lines.  Higher voltages require more spacing out of the wires.  Sometimes, a double-circuit is installed where a single circuit used to be, or perhaps the new structures are build with a provision for future doubling.

Based on my own observation, it seems that for new construction nowadays, lattice structures are pretty much only used for 500kv and higher (maybe 345kv), and sometimes monopoles are used even then.