Exit numbers and wind loading on new signs

[DTComposer]

When I was in Southern California last week, I drove past this sign:

https://www.google.com/maps/@33.8611476,-117.8770011,3a,75y,336.92h,96.01t/data=!3m7!1e1!3m5!1stKZ37tS-iUM-uEJzy6o_lg!2e0!5s20140601T000000!7i13312!8i6656

This is relatively new (~2 years), and if you scroll through the Google Street View history, you'll see the 2012 version:

https://www.google.com/maps/@33.8611476,-117.8770011,3a,75y,336.92h,96.01t/data=!3m7!1e1!3m5!1s0t5HEzjPbmTMHlzMtmXV5g!2e0!5s20120101T000000!7i13312!8i6656

The truss has been replaced but the new one appears to be the same size, or perhaps a little larger. The sign, however, is obviously taller, in order to accommodate the exit number, and spills over the top of the new truss.

So my question is this: Caltrans said they were putting the exit numbers in the body of the sign rather than in a tab on top of the sign because they were cautious about wind loading. But wouldn't this assembly put the lie to that idea, particularly since this is in an area prone to high winds (i.e. Santa Ana Winds)? I saw numerous other assemblies like this during my drives last week.

[myosh_tino]

When I was in Southern California last week, I drove past this sign:

https://www.google.com/maps/@33.8611476,-117.8770011,3a,75y,336.92h,96.01t/data=!3m7!1e1!3m5!1stKZ37tS-iUM-uEJzy6o_lg!2e0!5s20140601T000000!7i13312!8i6656

This is relatively new (~2 years), and if you scroll through the Google Street View history, you'll see the 2012 version:

https://www.google.com/maps/@33.8611476,-117.8770011,3a,75y,336.92h,96.01t/data=!3m7!1e1!3m5!1s0t5HEzjPbmTMHlzMtmXV5g!2e0!5s20120101T000000!7i13312!8i6656

The truss has been replaced but the new one appears to be the same size, or perhaps a little larger. The sign, however, is obviously taller, in order to accommodate the exit number, and spills over the top of the new truss.

So my question is this: Caltrans said they were putting the exit numbers in the body of the sign rather than in a tab on top of the sign because they were cautious about wind loading. But wouldn't this assembly put the lie to that idea, particularly since this is in an area prone to high winds (i.e. Santa Ana Winds)? I saw numerous other assemblies like this during my drives last week.

California's sign trusses with a frame depth of 106" have been able to support sign panels with heights of 100", 110" and 120" since 1981.  Prior to 1981, Caltrans had in their standard plans, specs for trusses with frame depths of 116" for 110" signs and 126" for 120" signs.  In those cases, the top of the sign matched the top of the truss.  After 1981, only the 100" tall sign matched the top of the truss.  The 110" and 120" tall signs always protruded above the top of truss.

Here's an illustration that should help explain what I mean by "frame depth"...

So the sign you saw last week appears to be a 120" tall sign mounted on a new truss with a frame depth of 106".  There is no violation of wind-loading standards since that truss was designed to accommodate a sign of that height.

It should also be noted that all new trusses are able to support external exit tabs but there is no "detail" (i.e. plans) on how to mount them.  Part of the problem is there are still numerous older trusses and other sign structures out in the field which cannot handle external tabs and until those are taken out of service, no detail can be developed.

[DTComposer]

That does help explain it. Thank you - I really appreciate the detailed response!

[vdeane]

It should also be noted that all new trusses are able to support external exit tabs but there is no "detail" (i.e. plans) on how to mount them.  Part of the problem is there are still numerous older trusses and other sign structures out in the field which cannot handle external tabs and until those are taken out of service, no detail can be developed.

Why not?  Just put in a note saying "this detail not to be used on older trusses" (and didn't other states use the same trusses with external tabs?  What makes CA special?).  At the rate CA is going, once the old trusses are gone, the wind loading standards will have changed again, and so development of a proper exit tab would be delayed yet again.  And if by some miracle one ever does get developed, it probably won't be pervasive at any point in my lifetime.

[andy3175]

In the thread about the signs at US 101 and SR 110 in Los Angeles (https://www.aaroads.com/forum/index.php?topic=14190.msg2026017), Chris Sampang mentioned a particular sign bridge that was notable in that thread for the message inside its sign panel.

But relevant to Myosh's comments above (about frame depth) is that the sign bridge Chris identified in that thread (see https://goo.gl/maps/rANt9sMKput for Google Street View) is one of the oldest sign bridges left on the California state highway system. You can tell this by looking at fact the sign bridge has vertical supports rather than diagonal supports; you don't see vertical supports like this on newer sign bridges. This old sign bridge also happens to sport a newer external exit tab above it. I guess someone determined how to safely place the external exit tab on this very old sign bridge.

Another thought is that the 1971 Caltrans exit numbering experiment placed external exit tabs on a variety of sign bridges along 5, 10, 101, and 110. I don't know if those sign bridges were specially retrofitted to allow external exit tabs as part of that experiment or not. I also don't know if Caltrans developed some sort of installation protocol as part of that experiment.

[myosh_tino]

In the thread about the signs at US 101 and SR 110 in Los Angeles (https://www.aaroads.com/forum/index.php?topic=14190.msg2026017), Chris Sampang mentioned a particular sign bridge that was notable in that thread for the message inside its sign panel.

But relevant to Myosh's comments above (about frame depth) is that the sign bridge Chris identified in that thread (see https://goo.gl/maps/rANt9sMKput for Google Street View) is one of the oldest sign bridges left on the California state highway system. You can tell this by looking at fact the sign bridge has vertical supports rather than diagonal supports; you don't see vertical supports like this on newer sign bridges. This old sign bridge also happens to sport a newer external exit tab above it. I guess someone determined how to safely place the external exit tab on this very old sign bridge.

From the looks of it, the signs appear to be 100" tall.  As for the externally mounted exit tab, I don't think it was "safely" placed as trusses that old were probably not designed to accommodate external exit tabs.

Another thought is that the 1971 Caltrans exit numbering experiment placed external exit tabs on a variety of sign bridges along 5, 10, 101, and 110. I don't know if those sign bridges were specially retrofitted to allow external exit tabs as part of that experiment or not. I also don't know if Caltrans developed some sort of installation protocol as part of that experiment.

That's a good question probably best answered by someone at Caltrans.

Looking at some of these old signs in Google Street View, the supports for the external exit tabs appear to be composed of a horizontal piece spanning the depth of the truss and a vertical piece that would support the tab.  Current street view images show the old signs (https://goo.gl/maps/LiriQyTmwEw) with the 1971 exit tabs removed presumable because the old exit numbers did not match the new numbers.

[Brandon]

Some of the CalTrans requirements seem a bit silly when you look at another agency that resisted using exit numbering for slightly longer and decided to simply add the tabs to the top of the signs.  That agency is the Illinois State Toll Highway Authority (ISTHA).  ISTHA did not retrofit any trusses prior to adding the tabs, and the winds on the plains west of Chicagoland can be as fast as any Santa Ana wind.

Examples without tabs:
Basic ISTHA truss.
Front View
Side View

Basic ISTHA cantilever sign.
Front View
Side View

As you'll see, none of the supports are angled.  They're all completely vertical.

Examples with tabs:
Basic ISTHA truss.
Front View
Side View

Basic ISTHA cantilever sign.
Front View
Side View

In these cases, the supports were not replaced with exit tabs in mind.  All tabs were added well after the supports were installed.

As ISTHA was able to add exit tabs with no issues, there is no reason for CalTrans not to be able to do the same.

[vdeane]

I don't think California willingly decided to adopt exit numbers; I think exit numbers were shoved down their throats by the FHWA.  The "wind loading" issue is probably just a stalling tactic designed to ensure that they can keep on doing what they always have rather than fully embrace the exit numbered world.

[andy3175]

I don't think California willingly decided to adopt exit numbers; I think exit numbers were shoved down their throats by the FHWA.  The "wind loading" issue is probably just a stalling tactic designed to ensure that they can keep on doing what they always have rather than fully embrace the exit numbered world.

Although it's been slow going, Caltrans has included most of its replacement signs with the exit numbers. Exit numbers are generally added concurrently with the shift to retro-reflective sheeting. I think the nationwide shift to retro-reflective sheeting on guide signs has influenced Caltrans too. But with the agency's general lack of money, replacement of button copy non reflective signs to reflective signs has been a slow process ... one that began in 1999 and remains incomplete as of today. Having said that, significant sections of rural/small urban area freeways (i.e. freeways not in LA, Bay Area, or San Diego) -- such as SR 99 from Bakersfield to Sacramento that were fully button copy in 1999 -- are now seeing quite a bit of reflective signage. Last time I drove SR 99, it took over an hour before I encountered my first non reflective, older sign. That is not the case in the urban areas of the state, where quite a few freeways retain button copy. Signs appear to be replaced with major freeway construction projects, such as I-405 between I-105 and US 101 and I-5 through Burbank. The replacements generally meet or exceed the minimum requirements for exit numbering. But to your point, I would agree with your perception that Caltrans was not terribly interested in adding exit numbers, and when they decided to move forward with it in 2002, they did so in their own unique way, albeit slowly.

[SignBridge]

I've never really believed that Caltrans' issue with exit plaques was wind load. I think it's pure dollars and cents. It's probably cheaper overall to include the exit number within the sign than to manufacture a separate plaque and mounting hardware. I think that's all there is to it.

[jeffandnicole]

Windload.  I'm not sure if Caltrans' has ever stated there's an issue with windload, or if that's just an idea gone wild on these forums.

But, when I see this NJDOT structure with 3 medium sized signs: https://goo.gl/maps/6SAsa4yeKVF2 ...

eventually hold a medium sized sign and a large APL sign: https://goo.gl/maps/qMF7Fi6jBWF2

I tend to question the whole 'wind load' thing.  (And yes, that's the exact same structure for in both GSVs.)

[SignBridge]

Well those look like pretty strong gantries in the NJ photos. And the new APL sign looks bizarre.

[jeffandnicole]

Well those look like pretty strong gantries in the NJ photos. And the new APL sign looks bizarre.

It's a bit of a crowding issue for the 76 to 130/676 side because it's really only a temporarily sign.  But considering it was the first APL for the entire South Jersey area (and really was one of the first for an entire region), motorists didn't seem to have an issue figuring it out.

The center median support column is the only one I know of that supports both overhead gantries on either side of the support. (You may have to zoom in and move around a bit to see how it supports both gantries.)