GDOT "tips" overhead signs for reflectivity
Scott O. Kuznicki
GDOT has informed me that that is a standard installation for overhead
signs in Georgia. Apparently, there are upright H-channels and also
H-channels on the back of the sign panel as well. As to how they are
fastened to each other, I'm hoping they'll point me in the direction
of a standard or detail.
They said they tip them forward at the top to increase
visibility/reflectivity. I'm curious if there are indeed reflectivity
gains, since closing the angle of incidence to the viewing angle
actually reduces the retro-reflective effectiveness of the sign. Take
any sign and walk back and forth at a set distance from the sign; you
get the greatest reflectivity when standing off to the side. This is
why sign manufacturers have for years suggested installing signs at a
3° to 5° angle away from traffic (horiztonally). That is, the closest
edge (shoulder side) of the sign is further upstream than the furthest
edge (ditch side). But I've never seen documentation that said that
tipping the signs vertically was an acceptable practice, however.
Even with new ASTM Type 11 (diamond grade) sheeting, I would still
campaign for lighting on overhead signs. New headlamp designs (xenon,
HID, etc.) use European-type standards for light cutoff, seriously
limiting the amount of light that is thrown upward. This is a good
thing for oncoming traffic but a bad thing for reading unlit overhead
signs.
Scott O. Kuznicki
Civil (Traffic) Engineer
Dedicated Highway Enthusiast
Driving Enthusiast:
'03 525i 5-speed
'90 Ninja 250R (cheap fun!)
Stanley Cline
<scottk...@midwestroads.com> wrote:
>Regarding the overhead sign on IH 285 WB at the GA 400 SB underpass,
>GDOT has informed me that that is a standard installation for overhead
>signs in Georgia. Apparently, there are upright H-channels and also
>H-channels on the back of the sign panel as well. As to how they are
>fastened to each other, I'm hoping they'll point me in the direction
>of a standard or detail.
FWIW, I drove by the sign in question earlier today and it looks like
something was done to it such that it isn't leaning quite as much as
it was.
>They said they tip them forward at the top to increase
>visibility/reflectivity. I'm curious if there are indeed reflectivity
Tipping signs slightly is indeed a normal practice here.
>Even with new ASTM Type 11 (diamond grade) sheeting, I would still
>campaign for lighting on overhead signs. New headlamp designs (xenon,
GDOT hates lighting up *anything*. :(
-SC
--
Stanley Cline // Telco Boi // sc1 at roamer1 dot org // www.roamer1.org
"it seems like all you ever buy is Abercrombie and cell phones" --a friend
Scott O. Kuznicki
<sc1-...@roamer1.org> wrote:
> FWIW, I drove by the sign in question earlier today and it looks like
> something was done to it such that it isn't leaning quite as much as
> it was.
Could you grab a pic similar to the one I did on EB IH 285 just past
the overpass? I'm curious to see if it has changed in some way,
because GDOT tells me they found nothing wrong with it.
argatla...@yahoo.com.mx
> They said they tip them forward at the top to increase
> visibility/reflectivity. I'm curious if there are indeed reflectivity
> gains, since closing the angle of incidence to the viewing angle
> actually reduces the retro-reflective effectiveness of the sign. Take
> any sign and walk back and forth at a set distance from the sign; you
> get the greatest reflectivity when standing off to the side. This is
> why sign manufacturers have for years suggested installing signs at a
> 3° to 5° angle away from traffic (horizontally). That is, the closest
> edge (shoulder side) of the sign is further upstream than the furthest
> edge (ditch side). But I've never seen documentation that said that
> tipping the signs vertically was an acceptable practice, however.
Actually, the real reason manufacturers (and others) have suggested
signs should be mounted 5° off perpendicular (in the horizontal plane)
is that there are otherwise specular reflections which obscure the
message. This practice eliminates specularity by keeping the
horizontal entrance angle above 5°. The same rule also calls for
mounting signs perpendicular to the tangent on curved alignments, by
the way.
The 5° rule is systematically applied only in places (such as Britain)
where right-of-way constraints are so severe that signs are normally
mounted adjacent to the hard shoulder. In California, for example, the
usual mounting practice in rural areas is to put a ground-mounted sign
panel with its right-hand edge 30' in from the right-of-way fence
(where it is usually well out of the clear zone) and orient it
perpendicular to the road; the additional lateral clearance keeps the
entrance angle from dipping to zero.
I personally don't see a reason why G.D.O.T.'s practice of tilting the
signs forward should make much difference one way or another, because
the amount of light above the horizontal is fairly small (even with
loose American headlamp standards) compared to the amount of light
shining to the verge. I have seen forward tilt in some places (e.g.,
Arizona) but not others, and have noticed little difference.
> Even with new ASTM Type 11 (diamond grade) sheeting, I would still
> campaign for lighting on overhead signs. New headlamp designs (xenon,
> HID, etc.) use European-type standards for light cutoff, seriously
> limiting the amount of light that is thrown upward. This is a good
> thing for oncoming traffic but a bad thing for reading unlit overhead
> signs.
But even Germany has gotten rid of sign lighting as it has moved toward
microprismatic sheetings. In Britain, where permission has recently
been given to use microprismatic sheetings on Highways Agency
infrastructure (basically, the English trunk road system) without
applying for a Departure from Standard, sign lighting is basically
being retained only for action signs (such as final advance destination
signs, which are basically similar to our exit direction signs) as an
accommodation to lorry drivers and others who have to work with a large
observation angle.
bill
little lamps and just about all of it.
argatla...@yahoo.com.mx
> Britain lights EVERYTHING...If you've ever seen their signage they have
> little lamps and just about all of it.
They used to, but times are changing. The cute little luminaires for
ground-mounted signs (developed in the late 1950's and 1960's at the
same time the motorway signing system was being invented and
all-purpose road signing was being reformed) are on the way out except
in special situations such as "No entry" signs in front of lit shop
windows.