BNSF Signal Bridges

[GN_Fan]

Regarding the article about replacing BNSF’s last signal bridge in the Feb, 2022 issue of Trains, I’ve got a question that has been bothering me.  I’m no expert, but I would think that the only outdated part of the bridge would be the signal heads, electrical cabinets, and the associated wiring.  So for this 78 year old guy, I ask the question…why replace the entire bridge and replace it with a cantilever?  Why not just replace the signal components?  The only advantage I can see for a cantilever is that there’s room for adding another main track if need be.  Anyone have any thoughts on this?

[rdamon]

I have not read the article, but many of the bridges were replaced to have OSHA compliant ladders and fall protection added.

[mvlandsw]

Most of them are getting pretty old. There have been some fall down due to corrosion.

I don't see the advantage of the cantilever design. I've seen many freshly installed ones sagging obviously. The single heavy leg uses about the same amount of metal as two lighter ones would and a two legged version would be more stabile.

[mudchicken]

Clearance envelopes have changed together with multiple extra-dimensional moves being more common. Avoiding these old dinosaurs is becoming problematic. In the late 1950's, the model laws for clearances came into being, but were not uniformly kept from state to state. Old obstructions were "grandfathered-in". Their time is now up.

[diningcar]

mudchicken has identified the principal reason "clearance"; and the additional reason, decay of older structures. 

[Bruce Kelly]

Did the article in question actually claim it was BNSF's last signal bridge?

[diningcar]

The exact words were "and then, shockingly, only one was left in the entire Southwest"

[Bruce Kelly]

Fair enough. It would certainly not be THE last one on the BNSF system.