Wow that's nuts lol. Yeah that 10ft truss arm I found on the side of the freeway had a busted up cobrahead on it and the lamp survived and still works!
LOL that would be crazy if it did! Some members have taken pics of knockdowns like that that did still light though! Must not have been a Philips lamp in this since the arctube frame welds are very weak in those. The arc tubes often detach from the frame when the lights are mounted on bridges or whatever.
That's because the aluminum pole is much weaker than the galvanized steel bolts and concrete foundation that hold it into the ground. If you hit a steel pole hard enough, you do risk "uprooting" the foundation. Not entirely popping it out of the ground, but likely the anchor bolts will snap or the foundation will be cracked.
That's why breakaway bases are used on freeway light poles (aside from them being requited by law to protect motorists...). The breakaway couplings or cast aluminum transformer base is a sacrificial piece that snaps when the pole is hit, so the pole falls over. This saves the foundation and anchor bolts from damage and often times the pole can be reused (more so with steel than aluminum; the latter tends to get kinked up when it falls, either by its own weight or by being run over by the vehicle hitting it).
Breakaway bases are more important with steel poles than aluminum from both a safety and cost aspect. From the safety aspect, steel poles are not as likely to give way during an impact. So if a car hits a steel pole head-on at 80 MPH, if the car hits just right, that pole will literally saw the car in half length-wise. With aluminum, the pole would either just shear at the point of impact or get bend over like this one. If the impact is not strong enough, you'd just dent the aluminum pole and probably make it structurally deficient (if you bend it too much, it's stability decreases). With a breakaway base, that low-impact would still knock the pole over and the damage to the pole would be minor enough to allow its re-installation.
In some cases it doesn't make sense to have breakaway bases on poles though, such as with highmast lighting or overhead freeway signage. In those cases, they will install guardrails around the poles. RIDOT used to have highmasts on I-295 at the Rte 6 interchange before putting up cobraheads. Those highhmast poles actually had yellow sand barrels around them.
I wish they would just install guardrail around the light poles to protect them, but it all comes down to safety from the highway engineer's perspective. Allowing the poles to be sacrificial is safer than using guardrail since the guardrail makes the car stop short, which can be a dangerous impact. A light pole with a breakaway base reduces the force of that impact considerably. But with a big fat overhead sign pole, the guardrail is safer because if you were to put a breakaway base on a sign pole (the big overhead green signs) the impact from the sign falling over would be much more detrimental than someone eating the guardrail. Having the whole sign pole fall would crush other cars and block off the whole freeway.
Not to mention, a breakaway base can't be used with something that has high wind resistance. Light poles have a low EPA (effective projected area) which means they don't "catch" wind much. So a breakaway base can be used. With a big freeway sign, those suckers are effectively a wall blocking wind. If you used a breakaway base on one of those, if the sign caught enough wind it could topple the pole over. So breakaways are a bad idea for large signs. However, MassDOT uses (or used to use) breakaway bases for some normal-sized signs on freeways, such as exit number sign or a speed limit sign. Now they make shearing bolts for "normal" U-Channel traffic sign poles that will snap when the pole is it. That normally doesn't disturb the stub in the ground too much so the stub can be straightened out and a new pole attached to it, rather than have to pound a new pole into the ground.
This one is actually a fiberglass pole.
Originally this style of light had metal poles, but then they started using fiberglass instead (sometime in the 80's). Still plenty of the old poles around too.
I was by there this evening, and noticed that they had cut the pole off on this and hauled off the rest of it & the light (leaving 4-5 feet sticking out of the ground, no longer folded over at the base, but leaning at an angle...have no idea why they didn't cut it shorter)
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Then I have this pic of a hit streetlight where the entire concrete base was torn out of the ground...
Oh my good friend fiberglass lol. Hate that stuff.
I remember that pic! The pole must've been in pretty soft ground. Around here, it's mostly rock and clay in the ground. I've heard of some places with soft ground having issues with direct-bury poles leaning over time and having poles collapse in storms. Doesn't help that the pole was on a steep bank. I think on flat ground the foundation probably had a better chance. Those foundations are typically over 1ft X 1ft and up to 6ft deep, so it's in the ballpark of 1000 pounds. So in solid ground, that would be very hard to uproot. But in softer ground a large truck could totally kill it lol. Especially with a galvanized steel pole. With aluminum the pole would just shear apart. Sucks for the pole but at least is usually saves the foundation lol. The foundation is the most expensive part. You need to dig the hole, set the precast base, and then wait a couple week for the earth to compact around it, and then install a new pole anyway so you might as well make the pole sacrificial lol.
Update:
This was replaced last week. Same type of HPS fixture!
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@Mike:
Yep that one where the entire concrete was torn out was probably in relatively soft soil since that hill it was on would have been built up some.
The ground where I'm at which is closer to the mountains is hard & has allot of clay in it (and you always find rocks when digging .lol. )
Yeah Rhode Island (which is not in the mountains; not even within 100 miles of mountains I don't think) there's a lot of clay and rock in the ground too. I still see stuff lean though, usually because it's not buried properly (guy installing the post or whatever hit a rock and said "f*** it, this should be deep enough."
No pictures though this time because all that's lift is a stump of the pole, and some glass on the opposite side of the intersection (I'm guessing the county hauled off its remains).
I don't think whatever hit it was going at the 25mph speed limit for that neighborhood street...
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I shoulda driven by this one this evening to see if still lights
That's why breakaway bases are used on freeway light poles (aside from them being requited by law to protect motorists...). The breakaway couplings or cast aluminum transformer base is a sacrificial piece that snaps when the pole is hit, so the pole falls over. This saves the foundation and anchor bolts from damage and often times the pole can be reused (more so with steel than aluminum; the latter tends to get kinked up when it falls, either by its own weight or by being run over by the vehicle hitting it).
Breakaway bases are more important with steel poles than aluminum from both a safety and cost aspect. From the safety aspect, steel poles are not as likely to give way during an impact. So if a car hits a steel pole head-on at 80 MPH, if the car hits just right, that pole will literally saw the car in half length-wise. With aluminum, the pole would either just shear at the point of impact or get bend over like this one. If the impact is not strong enough, you'd just dent the aluminum pole and probably make it structurally deficient (if you bend it too much, it's stability decreases). With a breakaway base, that low-impact would still knock the pole over and the damage to the pole would be minor enough to allow its re-installation.
In some cases it doesn't make sense to have breakaway bases on poles though, such as with highmast lighting or overhead freeway signage. In those cases, they will install guardrails around the poles. RIDOT used to have highmasts on I-295 at the Rte 6 interchange before putting up cobraheads. Those highhmast poles actually had yellow sand barrels around them.
I wish they would just install guardrail around the light poles to protect them, but it all comes down to safety from the highway engineer's perspective. Allowing the poles to be sacrificial is safer than using guardrail since the guardrail makes the car stop short, which can be a dangerous impact. A light pole with a breakaway base reduces the force of that impact considerably. But with a big fat overhead sign pole, the guardrail is safer because if you were to put a breakaway base on a sign pole (the big overhead green signs) the impact from the sign falling over would be much more detrimental than someone eating the guardrail. Having the whole sign pole fall would crush other cars and block off the whole freeway.
Not to mention, a breakaway base can't be used with something that has high wind resistance. Light poles have a low EPA (effective projected area) which means they don't "catch" wind much. So a breakaway base can be used. With a big freeway sign, those suckers are effectively a wall blocking wind. If you used a breakaway base on one of those, if the sign caught enough wind it could topple the pole over. So breakaways are a bad idea for large signs. However, MassDOT uses (or used to use) breakaway bases for some normal-sized signs on freeways, such as exit number sign or a speed limit sign. Now they make shearing bolts for "normal" U-Channel traffic sign poles that will snap when the pole is it. That normally doesn't disturb the stub in the ground too much so the stub can be straightened out and a new pole attached to it, rather than have to pound a new pole into the ground.
Originally this style of light had metal poles, but then they started using fiberglass instead (sometime in the 80's). Still plenty of the old poles around too.
I was by there this evening, and noticed that they had cut the pole off on this and hauled off the rest of it & the light (leaving 4-5 feet sticking out of the ground, no longer folded over at the base, but leaning at an angle...have no idea why they didn't cut it shorter)
---
Then I have this pic of a hit streetlight where the entire concrete base was torn out of the ground...
I remember that pic! The pole must've been in pretty soft ground. Around here, it's mostly rock and clay in the ground. I've heard of some places with soft ground having issues with direct-bury poles leaning over time and having poles collapse in storms. Doesn't help that the pole was on a steep bank. I think on flat ground the foundation probably had a better chance. Those foundations are typically over 1ft X 1ft and up to 6ft deep, so it's in the ballpark of 1000 pounds. So in solid ground, that would be very hard to uproot. But in softer ground a large truck could totally kill it lol. Especially with a galvanized steel pole. With aluminum the pole would just shear apart. Sucks for the pole but at least is usually saves the foundation lol. The foundation is the most expensive part. You need to dig the hole, set the precast base, and then wait a couple week for the earth to compact around it, and then install a new pole anyway so you might as well make the pole sacrificial lol.
This was replaced last week. Same type of HPS fixture!
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@Mike:
Yep that one where the entire concrete was torn out was probably in relatively soft soil since that hill it was on would have been built up some.
The ground where I'm at which is closer to the mountains is hard & has allot of clay in it (and you always find rocks when digging .lol. )
No pictures though this time because all that's lift is a stump of the pole, and some glass on the opposite side of the intersection (I'm guessing the county hauled off its remains).
I don't think whatever hit it was going at the 25mph speed limit for that neighborhood street...
Like last time the stopsign was quickly replaced, but as of last week the light still had not been.