What are the mechanics behind wire hung stoplights?

[TheArkansasRoadgeek]

I have always wondered how places where wire hung stoplights are common, how they account for life-span, weather and other corosive factors. The assemblies seem fragile.

[myosh_tino]

Native Californian jumping in here...

The only "big" quake I've been through was the M6.9 Loma Prieta quake in 1989 and while that was some time ago, I do not remember any mast arms "falling apart" due to the shaking.  Any signal damage was most likely caused by falling debris from nearby buildings and that would have been confined to downtown Santa Cruz, Oakland where the Cypress structure failed and the Marina district in San Francisco.

With regards to span-wire vs mast arms in general, I would think the span-wire would be more susceptible to damage in an earthquake simply because if the two poles supporting the span-wire were to move in opposite directions, it would rip the span-wire from one of the two poles causing the signal(s) to fall to the ground.

[roadman65]

To change the subject a bit, but generally under the mechanics of wire hung stoplights why is Hillsborough County, FL doing away with the top cable as FL generally uses 2?  One up high  that seems to be load bearing with the one below mostly for the electrical.  The new ones in the Tampa area have only one wire.

Also to note Florida uses a small box in which they mount the head from which other states using span wire use only a hook although some lights in NY State do have what Florida has though.  That is odd itself as being the other states do not use them, its not a necessity except in parts of NY and most of FL.   

In addition you have both Carolinas that like to go cheapo and make their standard span wires look like temporary signals using wooden telephone poles over metal poles.  I am guessing NC and SC do not care about aesthetics and use the most cheap way to go to save money on their tax payers.

[US 89]

To everyone who is saying wire spans are better than mast arms in the wind: Florida installs mast arms with horizontal signals (such as the ones at FL 817 and 860 in Miami Gardens) because they have a low wind profile in the event of a hurricane.

Also, a few years ago a huge microburst hit the southwestern Salt Lake City suburbs. Photo 5 on the photo gallery on this KSL article shows what happened to the mast arms at one intersection.

[jakeroot]

^^^
Watched a few videos online. I've never noticed the "MINI" signs before, but sure enough, they're there.

Still, though, most people from most states only recognise two types of fuelling services: full, and self. I can say for sure that I've never seen a "MINI" sign here in Washington before (although I've never noticed them in Oregon, so I guess that's not saying much). In fact, most stations have signs that tell you to tap your horn if you need assistance (typically for those who are disabled). I hardly ever see stations with pumps labelled "FULL".

[jeffandnicole]

Since we're talking about two different things here:

Wires vs. Mast Arms

Is it absolute fact that Florida switched to mast arms due to hurricanes?  Or do people just make assumptions?  Delaware is switching to mast arms, and they are definitely not a hurricane-prone state.  There can be other reasons behind the switch.  Same thing with California and earthquakes...Mast arms falling to pieces is very unlikely because of how they are made.  Heck, they get hit by a truck and usually fall down in one piece.

"Full" Service

In NJ, it's all known as Full Service gas, even though the only service you'll get is the gas pumped.

While the 'service' you received may be different from what was offered decades ago, the terminology hasn't changed.

[roadfro]

I think one element in favor of mast arms is that there is less actual maintenance of the signal structure. With wire spans, they generally need to be inspected every so often to ensure the support wires are still at adequate tensile strength. Mast arm signals need no such maintenance. So after a weather event such as a major windstorm or hurricane, safety reasons would dictate inspection of any span wire installations but mast arms should be fine.

Also, a few years ago a huge microburst hit the southwestern Salt Lake City suburbs. Photo 5 on the photo gallery on this KSL article shows what happened to the mast arms at one intersection.

To be fair, it appears (from the photo on the article) that those signals came down as a result of the power lines falling down and taking the signals (one mast arm and another mast with mast arm intact) with them. It does not appear that the mast arms failed as a result of the microburst.

[roadman65]

Since we're talking about two different things here:

Wires vs. Mast Arms

Is it absolute fact that Florida switched to mast arms due to hurricanes?  Or do people just make assumptions?  Delaware is switching to mast arms, and they are definitely not a hurricane-prone state.  There can be other reasons behind the switch.  Same thing with California and earthquakes...Mast arms falling to pieces is very unlikely because of how they are made.  Heck, they get hit by a truck and usually fall down in one piece.

"Full" Service

In NJ, it's all known as Full Service gas, even though the only service you'll get is the gas pumped.

While the 'service' you received may be different from what was offered decades ago, the terminology hasn't changed.

Also MD has for some time switching themselves from the span wire to mast arms, and PA, I believe, although I am not totally sure on that one as there may be places in Western PA that use span wires still.   I also know that SE PA has always used mainly mast arms and I once heard here that was a PennDOT district requirement as the DOT region handles Montgomery, Chester, Bucks, Delaware, and Philadelphia said no to span wires decades ago.

Also FL does still install new span wires, like I said Hillsborough County has adopted single wire hanging and even one intersection in that county has replaced a mast arm assembly with a span wire.  SR 574 and Williams Road in Mango just removed the old mast arms that were there since the early 90's when that road was made six lanes with the traditional FL concrete poles and two tier wiring.   Even in Orlando and Kissimmee some mast arms were switched back to span wire assemblies too.

FDOT told me years ago its not a mandate, even though Miami-Dade and Monroe adopted them for use because of Andrew in 94.  Those are horizontal signals they used there that prove to be better and not just the arm over the wires.   Keep in mind some places use the GA box set up with a square wire box with four wires tugging from the four corners that help keep the wires stable during high winds as well as the "x" installation where there are two diagonal wires meeting in the middles as both wires keep each other in check in high winds.

[Scott5114]

VDS is a several-thousand dollar solution to a host of problems, most of which could be solved by paying someone $10 to go out and program the lights to go to flash mode at the appropriate times.

[TheArkansasRoadgeek]

You did not address my point with regards to California using mast arms. They see major earthquakes far more often than any other contiguous US state, yet I don't think I've ever seen an image of a fallen mast arm. Live wires can present an issue too. At least the mast arms protect the wiring. If a wire-span mast topples over, you'll have wires all across the street. And if the mast falls in the wrong direction, it could rip the wiring apart. That's doubly dangerous.

I posted in Road-Related Illustrations in the Design Manuel I posted referred to a Viberation Mitigation Device that resides within the mast arm and pole (in Arkansas' case, in is a sign). I am not saying that an earthquake would have no effect on the structure, but it should be able to ride out the event. I watched a video of a mast arm with and without the mitigation measures, the arm and pole were doing quite the jig.

[jakeroot]

You did not address my point with regards to California using mast arms. They see major earthquakes far more often than any other contiguous US state, yet I don't think I've ever seen an image of a fallen mast arm. Live wires can present an issue too. At least the mast arms protect the wiring. If a wire-span mast topples over, you'll have wires all across the street. And if the mast falls in the wrong direction, it could rip the wiring apart. That's doubly dangerous.

I posted in Road-Related Illustrations in the Design Manuel I posted referred to a Viberation Mitigation Device that resides within the mast arm and pole (in Arkansas' case, in is a sign). I am not saying that an earthquake would have no effect on the structure, but it should be able to ride out the event. I watched a video of a mast arm with and without the mitigation measures, the arm and pole were doing quite the jig.

Very cool. If you could post a more specific link to the vibration mitigation device, that'd be sweet. I can't seem to find it.

I'm not quite sure what these vibration mitigation devices are capable of, but if they keep the mast from vibrating and/or toppling over (like a tuned mass damper), certainly that would negate the necessity to worry about high winds and, depending on the strength, earthquakes. It would also allow VDS systems to work better in windy locations (as it's apparently an issue, judging by posts above).

[TheArkansasRoadgeek]

You did not address my point with regards to California using mast arms. They see major earthquakes far more often than any other contiguous US state, yet I don't think I've ever seen an image of a fallen mast arm. Live wires can present an issue too. At least the mast arms protect the wiring. If a wire-span mast topples over, you'll have wires all across the street. And if the mast falls in the wrong direction, it could rip the wiring apart. That's doubly dangerous.

I posted in Road-Related Illustrations in the Design Manuel I posted referred to a Viberation Mitigation Device that resides within the mast arm and pole (in Arkansas' case, in is a sign). I am not saying that an earthquake would have no effect on the structure, but it should be able to ride out the event. I watched a video of a mast arm with and without the mitigation measures, the arm and pole were doing quite the jig.

Very cool. If you could post a more specific link to the vibration mitigation device, that'd be sweet. I can't seem to find it.

I'm not quite sure what these vibration mitigation devices are capable of, but if they keep the mast from vibrating and/or toppling over (like a tuned mass damper), certainly that would negate the necessity to worry about high winds and, depending on the strength, earthquakes. It would also allow VDS systems to work better in windy locations (as it's apparently an issue, judging by posts above).

Here is Arkansas' mast arm and stoplight standards

*In the document (zoom required (Ctrl +)) it references many things, but what piece you are looking for is right-center page, there it spells out the taper of the mast arm and the "Vibratory Mitigation Device" (in this case, it appears to be a possibly weighted sign). Other setups have the device within the pole and/or arm. See here

I am sure other states have a similar manuel. The Standard Roadway Drawings (for Arkansas) has a table of contents and a directory with the corresponding letter-letter-number (SD-9) designation with it in sequential (decending) order if you would like to read more into it.