question about traffic lights with horizontal louvers/slats

[Todd Brassman]

My city has been installing traffic signals recently with horizontal
louvers or slats on them. These slats don't look much like the little
covers on the tops of older-style lights. There are maybe four or five
slats per individual light.

What is the purpose of these slats? They don't seem to cut down on
glare and, to me at least, they make the lights significantly more
difficult to see.

My town has switched over to LED based lights over the last few years if
that makes a difference. Also, not all lights here have these slats.

[Scott en Aztlán]

Post by Todd Brassman
My city has been installing traffic signals recently with horizontal
louvers or slats on them. These slats don't look much like the little
covers on the tops of older-style lights. There are maybe four or five
slats per individual light.
What is the purpose of these slats? They don't seem to cut down on
glare and, to me at least, they make the lights significantly more
difficult to see.

Yes, that is the purpose. They want to make it harder for people who
are not sitting directly in front of the lights to see.

[Alan]

On Wed, 16 Aug 2006 21:46:02 -0700, Scott en Aztlán

Post by Scott en Aztlán

Post by Todd Brassman
My city has been installing traffic signals recently with horizontal
louvers or slats on them. These slats don't look much like the little
covers on the tops of older-style lights. There are maybe four or five
slats per individual light.
What is the purpose of these slats? They don't seem to cut down on
glare and, to me at least, they make the lights significantly more
difficult to see.

Yes, that is the purpose. They want to make it harder for people who
are not sitting directly in front of the lights to see.

But, horizontal slats won't do anything for that!

Vertical slats would prevent people who aren't directly in front of
the light from seeing the light. That would seem to apply to most
intersection-viewing situations.

Alan

==

It's not that I think stupidity should be punishable by death.
I just think we should take the warning labels off of everything
and let the problem take care of itself.

--------------------------------------------------------

[Bill Bolton]

Post by Alan

Post by Scott en Aztlán
Yes, that is the purpose. They want to make it harder for people who
are not sitting directly in front of the lights to see.

But, horizontal slats won't do anything for that!

Yes, they indeed do!

The slats are usually titled downwards slightly so that the light is
only visible between the slats when you are close(r) to it and looking
somewhat upwards at it.

They are often used where there are several set of successive traffic
lights visible along a road at the same time, i.e. on a long straight
road with a falling grade in the direction of travel.

They encourage drivers to pay attention to each set of lights as they
approach them, instead of seeing a distant green light while missing a
closer red light.

Post by Alan
Vertical slats would prevent people who aren't directly in front of
the light from seeing the light. That would seem to apply to most
intersection-viewing situations.

Vertical slats are primarily useful for "turning lane", and similar
situations, when you need to be more of less directly "on axis"
horizontally in a particular lane to the light in order to be able to
see it.

Slatted traffic lights have been in use for specific purposes around
Sydney for several decades.

Cheers,

Bill

Bill Bolton
Sydney, Australia

[Stephen Sprunk]

Post by Todd Brassman
My city has been installing traffic signals recently with horizontal
louvers or slats on them. These slats don't look much like the little
covers on the tops of older-style lights. There are maybe four or five
slats per individual light.
What is the purpose of these slats? They don't seem to cut down on
glare and, to me at least, they make the lights significantly more
difficult to see.
My town has switched over to LED based lights over the last few years if
that makes a difference. Also, not all lights here have these slats.

The slats are used where there is a need to prevent people from seeing the
light when it doesn't apply to them.

Horizontal slats are frequently used where you have two lights close
together, e.g. a block or less, so that people don't see a distant green and
ignore the closer red. The slats prevent you from seeing the color of the
second light until you've passed the first one, reducing confusion.

Vertical slats are used here to keep drivers in the through lanes from
seeing the possibly-differing indication in a turn lane. Here it's common
for a left turn lane to get a solid green (not arrow) when the through lanes
have a solid red; if the through drivers could see the solid green, they
might enter the intersection and get whacked by an opposing driver turning
left on a green arrow.

Slats have been used in Texas for at least a decade, though they're getting
more common lately. The newest lights actually forgo the slats and use a
series of mesh screens which are lined up such that they have the effect of
both horizontal and vertical slats. There's virtually no fade-in/out as you
move in/out of the visible area -- you either see 100% of the light or 0% of
it, unlike with slats where the change in visibility is gradual.

S

[Ned Carlson]

Post by Stephen Sprunk
Horizontal slats are frequently used where you have two lights close
together, e.g. a block or less, so that people don't see a distant green and
ignore the closer red. The slats prevent you from seeing the color of the
second light until you've passed the first one, reducing confusion.

Yeah, that's something the City of Chicago needs to use more often,
there's a number of intersections here with diagonal streets that have
multiple lights, as well as intersections under/over expressway
entrances.

Whatever happened to the polarized lenses I used to see on
stoplights?

[Stephen Sprunk]

Post by Ned Carlson

Post by Stephen Sprunk
Horizontal slats are frequently used where you have two lights close
together, e.g. a block or less, so that people don't see a distant green
and ignore the closer red. The slats prevent you from seeing the color
of the second light until you've passed the first one, reducing
confusion.

Yeah, that's something the City of Chicago needs to use more often,
there's a number of intersections here with diagonal streets that have
multiple lights, as well as intersections under/over expressway
entrances.

Diagonal streets would probably benefit most from stacked mesh grilles on
the lights; they combine the effects of both horizontal and vertical slats.
Very rare here, since we don't have many diagonal streets, but remarkably
effective.

Post by Ned Carlson
Whatever happened to the polarized lenses I used to see on
stoplights?

I saw a lot of those installed in the 80s and early 90s, but virtually none
since then. Slats are probably a lot cheaper, they're easy to retrofit onto
existing lights, and don't require maintenance crews to stock two different
types of signals.

All the ones I saw had square hoods, though, which looked cool, and the
uniform color and intensity was refreshing compared to standard
bulbs/lenses. I really wish folks would put some sort of translucent cover
over LED traffic lights; being able to see the individual elements offends
my sense of aesthetics for some reason.

S

[John Mara]

Post by Stephen Sprunk
Slats are probably a lot cheaper, they're easy to retrofit onto
existing lights, and don't require maintenance crews to stock two different
types of signals.
All the ones I saw had square hoods, though, which looked cool, and the
uniform color and intensity was refreshing compared to standard
bulbs/lenses. I really wish folks would put some sort of translucent cover
over LED traffic lights; being able to see the individual elements offends
my sense of aesthetics for some reason.

I've noticed a problem with LED signals that have slats. Blowing snow
packs in between the slats and the LEDs don't make enough heat to melt
it. Sometimes the light is barely visible.

John Mara

[James Robinson]

Post by Stephen Sprunk

Post by Ned Carlson
Whatever happened to the polarized lenses I used to see on
stoplights?

I saw a lot of those installed in the 80s and early 90s, but virtually
none since then. Slats are probably a lot cheaper, they're easy to
retrofit onto existing lights, and don't require maintenance crews to
stock two different types of signals.
All the ones I saw had square hoods, though, which looked cool, and
the uniform color and intensity was refreshing compared to standard
bulbs/lenses. I really wish folks would put some sort of translucent
cover over LED traffic lights; being able to see the individual
elements offends my sense of aesthetics for some reason.

I think you will find that they weren't polarized, but used fresnel
lenses. They are called "Programmed visibility signals". 3M was the
manufacturer:

http://massroads.com/3m_pv.shtml

When they are installed, the back of the signal head is opened, and there
is a projected image of the signal's field of view on a frosted screen.
The areas where they don't want the signal to be seen are covered with a
masking material.

[Robert Coe]

On Fri, 18 Aug 2006 11:09:00 -0500, "Stephen Sprunk" <***@sprunk.org>
wrote:
: All the [LED lights] I saw had square hoods, though, which looked cool,
: and the uniform color and intensity was refreshing compared to standard
: bulbs/lenses. I really wish folks would put some sort of translucent
: cover over LED traffic lights; being able to see the individual elements
: offends my sense of aesthetics for some reason.

Well, you may say that now, while you're young. But as you get older, the
ability to resolve the separate elements will become a source of reassurance
and pride - until eventually you lose that ability and the LEDs just look like
a single (slightly fuzzy) light. :^(

Me, I see *two* lights (of the same color) unless I'm wearing my bifocals.

Be careful what you wish for. You may get it. ;^|

[Stephen Sprunk]

Post by Robert Coe
On Fri, 18 Aug 2006 11:09:00 -0500, "Stephen Sprunk"
: All the [LED lights] I saw had square hoods, though, which looked cool,

That [LED lights] was supposed to be the 3M "programmable" lights; I
wrote polarized, which was indeed incorrect.

Post by Robert Coe
: and the uniform color and intensity was refreshing compared to standard
: bulbs/lenses. I really wish folks would put some sort of
translucent
: cover over LED traffic lights; being able to see the individual elements
: offends my sense of aesthetics for some reason.
Well, you may say that now, while you're young. But as you get older,
the ability to resolve the separate elements will become a source of
reassurance and pride - until eventually you lose that ability and the
LEDs just look like a single (slightly fuzzy) light. :^(

I was born with 20/10 vision and it's dropped to 20/15 now; I'll feel
blind when it drops to 20/20 ;-)

Post by Robert Coe
Me, I see *two* lights (of the same color) unless I'm wearing my bifocals.
Be careful what you wish for. You may get it. ;^|

Unfortunately, I also have permanent double vision. I can force my eyes
to cut it down to one image when I need to, but it hurts like it hurts
you to cross your eyes for more than a few seconds. If a light is near
the edge of my sunglasses, that makes four images, and if I'm on my
motorcycle, the visor sometimes doubles it again to eight (though only
near the edges). And each one has dozens of little elements... I
_never_ miss traffic lights because they're _everywhere_ ;-)

S