Types of Sign Supports: Which Ones Are the Best?

[Amaury]

For the purposes of this thread, I'm only talking about the ground-mounted ones. How many types of supports are there and what are they called? Also, which ones are the most reliable, in your opinion? I think I already know most of them, I just don't know what they're all called. Unless otherwise stated, I'm going by the ones I've seen in Washington, though I'm sure it's universal, for the most part.

You have what I think are the standard wooden ones:
https://maps.app.goo.gl/7Vn2iGV6v6hVrtJK6
https://maps.app.goo.gl/qUHzjv4WjyTNUzys8

On the wooden ones, what are the holes you sometimes see on the side for, though? Or are they just there? I don't always see them, though I guess for those ones, it's because they're farther down in the ground. It also looks like the wooden ones have two ways of the signs being attached to them: one way is with the little "panel" seen in that second one, and the other way is by screwing the sign directly into the post.

You have the solid metal ones, though I don't know what they're called:
https://maps.app.goo.gl/twm9RUVNANPT7bgj7
https://maps.app.goo.gl/aS1j9U2rPWAtsBX67

You have the holed metal ones, which I have found out are called telespar posts:
https://maps.app.goo.gl/Grcy4mUtzw2RcLVh6
https://maps.app.goo.gl/r9Cx8i2herTR1Ss67

You've got these metal ones that dip on the side, usually done in twos and for the bigger signs, that seem to be a two-part assembly, with the kind of "spider feet" legs:
https://maps.app.goo.gl/EWwkstUSPm6JErWZ6

Then you've got these thicker metal posts ones, though the cons with these is that the signs can get misaligned because of the way they're attached to the post, as seen with the trucks sign here:
https://maps.app.goo.gl/5qB2PoHvSo8Byj3a7

I've been able to see a professional installation video of the telespar post, as well as a video for the "dipped metal" ones with the separate metal assemblies. The closest thing I've found for the wooden one is this:

https://www.youtube.com/watch?v=koRKCBMi2hU

It doesn't show the full installation, though. Do the wooden posts anchor to anything, like how the telespar posts have the base and then the sideways screws to secure the sign to the base? How deep are the holes? I am very curious about this.

I did come across an article that said wooden posts are generally more reliable, specifically for the wintertime since they apparently do better when, for example, snowplows are going by and aren't hitting the signs directly, but are hitting them with the snow that's being plowed. That surprises me since they're prone to wood rot and can snap as a result.

[Scott5114]

On the wooden ones, what are the holes you sometimes see on the side for, though? Or are they just there? I don't always see them, though I guess for those ones, it's because they're farther down in the ground.

I suspect these holes are to create a natural weak point low to the ground, so that if they are struck by a vehicle, they snap off at that point. If they aren't there, there's the risk they would snap higher up and send the part of the post with the sign through the windshield.

This also explains the "spider feet" on the I-beam posts; the bolts connecting the feet to the anchor are designed to shear off in a collision. These are usually paired with a hinge higher up (usually just below the sign). When struck, the vehicle shears the post off of the base and then causes the lower half of the post to swing upward, allowing the vehicle to pass under the sign (which then will fall to the ground behind the vehicle).

Breakaway mechanisms like this are mandated under federal safety rules for anything placed in the highway's clear zone (which usually corresponds to DOT right-of-way). Anything in the clear zone which cannot be fitted with a breakaway mechanism must be protected by a guardrail.



Nevada uses a very particular mounting arrangement that as far as I know, no other state uses. https://www.google.com/maps/@36.0102138,-114.7676025,3a,52.7y,11.84h,87.9t/data=!3m6!1e1!3m4!1swBn3BwAKtsmF2y6IQ6HZBQ!2e0!7i16384!8i8192?entry=ttu I'm kind of curious what led them to adopt this setup.

[J N Winkler]

The width of the clear zone varies with the design speed, and I believe it is 30 feet at 70 MPH.  Thus, for any sign support located immediately behind the freeway shoulder or in a median narrower than 60 feet, typically guardrail will be provided or passively safe supports will be used.  In North America the latter has traditionally meant slip bases or posts designed to break at grade.  However, many European countries use Lattix posts, which have a distinctive "woven aluminum" appearance and deform to absorb energy when hit--they are not mounted on slip bases at all.  This is a competitive field, with ongoing R&D and product innovation.

As for specific examples:

*  The drilled holes in wood posts go all the way through and are indeed designed to allow the post to break off when hit.  I typically see them set into concrete that does not extend above grade.  Because wood posts can rot, twist, and warp, choice of suitable wood species and timber preservatives is an ongoing research area for state DOTs.

*  I've always assumed the rear posts on the Nevada signs were provided for wind bracing.  Minnesota used to do much the same, but has recently switched to Telespar with finned bases in the ground.

*  The Texas universal triangular slip base (with three screws that hold the post in place and shear off when it is hit) is used outside Texas, notably in Colorado.

[Amaury]

It also looks like the wooden ones have two ways of the signs being attached to them: one way is with the little "panel" seen in that second one, and the other way is by screwing the sign directly into the post.

Some examples.

This one is the first one. It looks like it slides in on the "panel" on the post and then it looks like it's anchored with screws and nuts on both sides of the post, and it's the same if there's more than one wooden post for the sign:
https://maps.app.goo.gl/cdY8EfGBhzPoUHhx9
https://maps.app.goo.gl/VMpbsMh7igof2cG86

An example of the screwed in ones, which looks to only be done on the single-post signs:
https://maps.app.goo.gl/85ez6ZkVrn1HEGCn8
https://maps.app.goo.gl/wiHnzyRXiUZqsHk19

And then it looks like you have some that are reinforced with some extra metal, such as this one: https://maps.app.goo.gl/zM6ULt5XdKkvKH1k7

I think I've also seen some with two extra pieces of metal, one going horizontally and the other vertically. I just can't find any examples.

These are usually paired with a hinge higher up (usually just below the sign).

That's probably what these grooves in the wood are, then, on the signs with wooden posts that use two or more posts: https://maps.app.goo.gl/VMpbsMh7igof2cG86 It's the equivalent of the hinge you mentioned.

They're not seen on the posts for these two signs, but that's likely a combination of because there's a guardrail, like you mentioned, and because it's also within the City of Ellensburg, where there's a lower speed limit of 40 MPH in that section:
https://maps.app.goo.gl/7BfLwgNZJJJ3aBQG7
https://maps.app.goo.gl/bpJYxBVevd4wd9yE6

[J N Winkler]

Some examples.

This one is the first one. It looks like it slides in on the "panel" on the post and then it looks like it's anchored with screws and nuts on both sides of the post, and it's the same if there's more than one wooden post for the sign:

https://maps.app.goo.gl/cdY8EfGBhzPoUHhx9

https://maps.app.goo.gl/VMpbsMh7igof2cG86

An example of the screwed in ones, which looks to only be done on the single-post signs:

https://maps.app.goo.gl/85ez6ZkVrn1HEGCn8

https://maps.app.goo.gl/wiHnzyRXiUZqsHk19

And then it looks like you have some that are reinforced with some extra metal, such as this one:

https://maps.app.goo.gl/zM6ULt5XdKkvKH1k7

These examples all relate to how the sign panel is (or is not) stiffened to enhance wind resistance, which is really a separate issue from how the sign support is made crashworthy.

It appears that Washington state favors stiffener ribs for large panel signs, since the sign substrate consists largely of sheet aluminum.  New York and Virginia employ similar approaches.  Other states rely on extrusion flanges (Kansas), rigid frames (Nevada, California), or multilayer construction (as with the laminated panels used in California and Pennsylvania).

For small signs made out of sheet aluminum, it appears Washington caters to three different levels of wind load.  In descending order:

*  Stiffener flanges bolted or spot-welded to the back of the sheet aluminum (Wyoming uses this as well)

*  Horizontal straps that run from one side of the sign to the other around the back of the post (also very common for small signs in California; the disadvantage of this approach is noticeable bowing across the signface)

*  No stiffening at all (used to some extent in pretty much every state that uses sheet aluminum for small signs)

There are also variations in the extent to which fasteners such as screws and washers are visible against the signface.  In much of Europe, it is now considered unacceptable for fasteners to be seen at all, which has led to stiffeners being spot-welded instead of riveted or screwed into place.  Very few state DOTs in the US are this persnickety, though Colorado has used countersunk fasteners that are then covered with tiny dots of retroreflective sheeting.

[Scott5114]

In North America the latter has traditionally meant slip bases or posts designed to break at grade.  However, many European countries use Lattix posts, which have a distinctive "woven aluminum" appearance and deform to absorb energy when hit--they are not mounted on slip bases at all.  This is a competitive field, with ongoing R&D and product innovation.

I always kind of wondered what the deal with the Lattix posts was, and just thought it was a stylistic choice rather than a crashworthiness one. Do you know offhand whether Lattix posts would meet US crashworthiness guidelines?

I've always assumed the rear posts on the Nevada signs were provided for wind bracing.  Minnesota used to do much the same, but has recently switched to Telespar with finned bases in the ground.

That was my guess as well, but it seems kind of strange to implement it as a statewide standard, even in parts of the state (like the Las Vegas Valley) where wind speeds high enough to warrant special consideration are not a regular occurrence.

[J N Winkler]

I always kind of wondered what the deal with the Lattix posts was, and just thought it was a stylistic choice rather than a crashworthiness one. Do you know offhand whether Lattix posts would meet US crashworthiness guidelines?

I haven't found any indication that they have been tested for use in the US.  However, they are used extensively in Britain, where the Design Manual for Roads and Bridges has long specified NCHRP 350 as an accepted alternative to the EU crashworthiness standard.

I suspect there may be issues with using Lattix in the US since it is considered a proprietary design.

That was my guess as well, but it seems kind of strange to implement it as a statewide standard, even in parts of the state (like the Las Vegas Valley) where wind speeds high enough to warrant special consideration are not a regular occurrence.

I think statewide implementation may have to do with limiting the number of different standard designs that have to be catered for.  This said, a casual check in StreetView suggests to me that they use the same basic structure with both fixed bases outside the clear zone and slip bases in the clear zone.

[Amaury]

Another question I have would be how they decide which types of sign supports to use when they install signs? Does it depend on the landscape and such or is it just a random choice? I do realize that the wooden posts are the best in terms of costs, as they are the most inexpensive out of all of the posts and I think are simple to install.

I ask because some of the signs that have been recently repaired in my state were installed with different posts than they originally or previously had. Some that originally had telespar posts were repaired with wooden posts or vice-versa, and so on. For example, while I still don't know exactly what broke one of the signposts here since the sign is protected by a guardrail, when they repaired it, they repaired it with telespar posts instead of with the original wooden posts that it had:
https://maps.app.goo.gl/XE9VNhWZJW7o5YCY7 (front)
https://maps.app.goo.gl/4U56A6czGZzHwgWb9 (back)

In some cases, where a sign has needed repairs more than once, the type of supports has changed multiple times.

For example, milepost 132 on I-90 westbound in Washington:
https://maps.app.goo.gl/gT437Q7zzpGTqYuy6 (wood, including captures before this one, though it looks like it was repaired once before this because the previous wooden post broke, as the one in this 2019 capture is a different color of wood than in like the 2008 capture)
https://maps.app.goo.gl/nousFvBzAA1ALAq59 (telespar after a brush fire burned the previous wooden post, which you can still see the base of it here)
https://maps.app.goo.gl/9ohV2Vh29GHuMGjRA (something happened, as seen in this 2022 capture, with it laying on the ground)
https://maps.app.goo.gl/vMzbY7vroEHoWqrQ6 (when it was repaired, it was once again wood)

Same thing with milepost 53 on I-90 westbound on Snoqualmie Pass. Wood -> telespar -> wood again when it was repaired last month.

And sometimes they appear to randomly change the posts on signs even though they're not necessarily needing repairs and are standing perfectly. At the junction of US 97 and WA 10, both of these signs originally had wooden posts: https://maps.app.goo.gl/Rv9nuPino77ZTAXS6 Sometime between that capture in 2012 and the next capture in 2015, the guide sign's posts were changed to the solid metal posts, while the cautionary sign's posts were changed to telespar posts: https://maps.app.goo.gl/wugsHsmsRW9DybJPA In 2019, the guide sign was on the ground: https://maps.app.goo.gl/9btWSsBpGSpFTEX79 But that was after it already had its posts changed. No changes to the posts after it was repaired.

In this case, it's always wood to something else, though. I've never seen an unbroken sign randomly change to wooden posts.

Sometimes signs that are exactly the same type of sign (big, for example) and are within the same vicinity are also different:
https://maps.app.goo.gl/K7ZfxxyEyxuY14tq9 (wooden posts, I-82 eastbound entrance at Exit 26)
https://maps.app.goo.gl/cK5jQSAMrZvHtwU68 (I-beam posts, I-82 westbound entrance at Exit 26)

So, I don't know. The types of supports signs are installed with, at least here in Washington, seem to be totally random, though wooden ones seem to be more common here in Washington. In Oregon, I've noticed metal ones seem to be more common, like the I-beam ones.

[kirbykart]

I don't think there are any wooden supports in New York. I've seen some in Pennsylvania and Maine though.

[Scott5114]

Another question I have would be how they decide which types of sign supports to use when they install signs?

Every state has a standard drawing book that includes the details of which types of posts are acceptable in each state and how they are to be installed. In Oklahoma, for instance, we have no wooden posts; all small signs are mounted either to plain round poles or telespar posts. Counties often tend to use U-channel posts because they are cheap and easy to drive into the ground, but the DOT doesn't use them. Texas, meanwhile, famously uses its "goalpost"-style mounting system anywhere they can.

I assume the exact post style that is used is selected from the options in the book by an engineer based on cost and the particulars of the situation (and possibly also personal preference).

[J N Winkler]

For knockdown replacements, I suspect it's often also a matter of what they have on hand at the maintenance depot.

[roadman65]

I noticed KDOT uses wooden supports for all Route shields and small guides.

The Garden State Parkway always used wood for aesthetics on ground poles and use the rust metal on overheads. 

Generally NJDOT uses mono tube poles for ground guides on large signs, but smaller signs the v shaped slot poles. 


FDOT uses H metal supports on both small and large freeway signing but aluminum mono tube on off freeway sign supports.

[Amaury]

Texas, meanwhile, famously uses its "goalpost"-style mounting system anywhere they can.

Not anywhere they can, but Washington has those in some places, but it is more rare.

I-90 eastbound Exit 85:
https://maps.app.goo.gl/TPLGgC7RcSq1spoL6 (front)
https://maps.app.goo.gl/hDW9seZBwcTFQM4C9 (back)

I-90 eastbound Exit 143:
https://maps.app.goo.gl/JFho4vs73oWQpXAk6 (front)
https://maps.app.goo.gl/AjG2PMwPeGSajyZR8 (back)

This one isn't the goalpost-like one you're talking about, but I think it's the only T-like one in the state. I'll have to double-check.

I-90 westbound Exit 143:
https://maps.app.goo.gl/pF8M6N8MRMc4kj8P9 (front)
https://maps.app.goo.gl/QLiksUkEhyc6ptYL9 (back)

I think there might be some more examples, but it's not very common here.

[kphoger]

Texas, meanwhile, famously uses its "goalpost"-style mounting system anywhere they can.

Except that (cross-posting from another thread), that is reportedly not as true as it used to be.

Texas has been getting away from goalposts the last couple of years and going to stacks, especially at intersections where only 2 numbered roads are involved.