In a completely predicable turn of events, the iconic Southern Pacific cantilever mast that has guarded the southern approach to the 4th and Kin St terminal in San Francisco has met its demise sometime between March and October of 2023, likely in conjunction with the erection of overhead electrification wires. It has been replaced by three LED searchlight dwarfs.
I've noticed that starting with Amtrak's New Haven to Boston electrification. recent North American electrification projects have included far more overhead clutter than those seen in Europe. Specifically the use of solid overhead beams to mount the wire brackets as opposed to cable spans. Cable spans don't tend to block signal sight lines as much, allowing existing signal placements to remain.
Anyway, I'm not sure if the 4TH ST cantilever was scrapped or donated to a museum, but as one of the last of its type in daily service, its loss is significant.
tbf using solid overhead beams (portals) leads to a far more reliable electrification system than the cable spans (i know them as 'headspans'). Here in the UK we are constantly reminded of this when heavy winds bring down wires on the ECML leading to multi-day disastrous disruption to service. Even without severe winds, headspans are simply a worse design because if one overhead line breaks or looses tension for whatever other reason, it brings down all the others on the same structure because everything is mechanically connected; the system is only in balance with all wires in tension.
ReplyDeleteI'll pretty much echo what Qw said above with some added info.
ReplyDeleteOn Amtrak's NEC the old PRR/NH electrification relied on "steady spans" between opposing poles to hold up the wires. If a train suffered a pantograph failure it would not only mess up the wires over the track it was on but might also snag the steady span and bring down the catenary on all tracks. On the new (2000) electrification between New Haven and Boston anywhere there was only two tracks poles on either side held the wire for just one track. Where there was more than two tracks overhead beams held the wires up. Each track had it's own catenary arm holding up the wire on that track. You will see this on the several three and four track sections. With each wire separate from the rest the chances of a pantograph failure bringing down the whole mess is a LOT less. NOTE - I used to work for Amtrak on the NEC as both a tower operator (Baltimore division) and as a train dispatcher (S office/CTEC Philadelphia) so I'm familiar with the ex PRR catenary system.
Regarding Caltrains they are using the same system that Amtrak used between New Haven and Boston. Where there are only two tracks poles on either side hold up only the wire for the adjacent track. Where you see cross track beams is where there are more than three tracks or in terminal areas like the 4th street station.
I should also note that Caltrains is using a constant tension weighted catenary system like the New Haven to Boston section on the NEC. Several years ago Amtrak upgraded a 10 mile section of old PRR variable tension catenary to weighted constant tension catenary. This was done in the Princeton Junction area. There you'll see cross track beams that replaced the steady spans. This allowed the track speed to be increased form 135 to 150. The old PRR variable tension catenary, which sags/loose in the summer and is tight to the breaking point in the winter, limits the track speed to 135 for the Acela. This was a test to see what it would take and cost (Hint: $$$$$$$$$$) to redo all the old PRR catenary on the NEC. I suspect rewiring of the old PRR will be done only on straight sections where 150 is possible.