

Ambulances will trigger green signal - santhanam1
http://www.bangaloremirror.com/bangalore/others/Ambulances-will-trigger-green-signal/articleshow/47449386.cms?

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616c
What's funny in certain countries (right now for me the GCC) is that people
believe if you flash with your brights at the right speed and frequency it
will automatically set them to green, or shorten the interval on the opposing
traffic direction so it goes green for you sooner.

Do other people believe this? I have watched people try for over 60 seconds or
more until giving up, and I find this hilarious even today.

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lojack
I could understand why people would believe this.

[http://en.wikipedia.org/wiki/Traffic_signal_preemption#Line-...](http://en.wikipedia.org/wiki/Traffic_signal_preemption#Line-
of-sight)

In the US at least, that is how a significant number of these systems work.
It's rather unlikely they would get the right frequency to trigger it, but
it's certainly possible.

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hoop
This is spot on and how it was where I grew up and was a volunteer
firefighter. IIRC, the visible strobes on our equipment we referred to as
"opticoms"

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toomuchtodo
Opticoms can be preempted with a strobe light using an IR filter; they don't
need to receive visible light to activate.

If the Opticom sequence is trivial, the hardware is easy. If its a complex
pattern, a 555 timer is required.

Sitting outside your local fire station recording video of the strobe pattern
on an emergency vehicle should be sufficient to determine the necessary
pattern (you step through frame by frame to identify the sequence).

The above is informational only. One should keep in mind that today, most
traffic lights will log the preemption with their central controller, and that
unauthorized use is illegal in most jurisdictions.

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bitJericho
A similar system is already in effect (for years) in my area of the US.

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monk_e_boy
has it been hacked?

~~~
gnu8
Indeed it has been hacked. All things have been hacked.
[http://www.textfiles.com/phreak/BOXES/box-
chro.txt](http://www.textfiles.com/phreak/BOXES/box-chro.txt)

~~~
modoc
Built one of these as a youth with some friends. Worked great:)

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madeofpalk
The traffic lights in Sydney are managed in a way to give priority to late-
running public transport.

I was impressed to find out the traffic light system in Sydney, Australia
(Sydney Coordinated Adaptive Traffic System -
[http://en.wikipedia.org/wiki/Sydney_Coordinated_Adaptive_Tra...](http://en.wikipedia.org/wiki/Sydney_Coordinated_Adaptive_Traffic_System))
has been exported around the world to cities such as Singapore, Dublin and
Hong Kong.

Interestingly enough,

~~~
winsome
SCATS is also used more than you might imagine in some US areas. SCOOT
([http://www.scoot-utc.com/HowSCOOTWorks.php](http://www.scoot-
utc.com/HowSCOOTWorks.php)) is a similar system used in a lot of locations
too.

~~~
JshWright
Those are some fantastic acronyms...

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NLips
Why doesn't the signal set all lights to red, leaving the junction clear for
the ambulance to go through?

The best reason I can think of is if the idea is to improve traffic flow in
general in favour of the ambulance (e.g. allow cars in front of the ambulance
to move on through the lights), but that quicklt becomes a much more complex
problem.

~~~
Hoff
Former EMS provider...

The laws on whether ambulances must stop at red lights and stop signs vary by
locality.

It's almost always legally your mess if you don't stop at a traffic control
device and are then involved in a collision — most laws and various insurance
or service policy requirements tend to require "due care" or "prudent" or
other such wording, and collisions are usually considered an adverse
indication.

I've always wanted the traffic signal in front of me to be green on approach.

This reduces the numbers of stopped cars in my path.

Some of the drivers of the stopped cars at intersections will attempt or will
perform odd or normally-unexpected maneuvers, sometimes leading to collisions.
But mostly the herd in front of me scatters short distances, and generally
resulting in intersection gridlock.

It's common practice in some areas to avoid using the siren in certain
situations, such as when passing to the right of the bulk of (stopped) traffic
waiting on a red, using the breakdown or turn lane at an intersection, for
instance. Some folks will hear the siren and immediately block that lane, or
they might turn into and collide with me.

The local traffic preemption systems all include a flashing indicator — a
rotating red beacon on a cross-arm or a pole, for instance — indicating that
the preemption request has been accepted and is occurring. This tells me that
the other lights are all red. Or it tells me that I'm approaching a non-
preempted light, and that the green in front of me might go red.

If the traffic lights are red and there's no preemption and no open and no
bypass lane, then some of the folks at the front of the herd will inevitably
not break that red, meaning local traffic gridlock, meaning that the ambulance
waits (with the siren off) for the light to change.

~~~
bryondowd
Just curious what you mean by 'some of the folks at the front of the herd will
inevitably not break that red'. I often wonder what I should do when I find
myself stuck someplace where I'm possibly in the way of an ambulance at a
light.

Most of the time it's as simple as everyone pulling to the right and letting
the ambo through the middle, but there's many situations where it just isn't
obvious what everyone should do.

It would be great if there was an illustrated guide out there somewhere. I may
have to look around.

~~~
DanBC
In England:
[http://www.bluelightaware.org.uk/?p=239](http://www.bluelightaware.org.uk/?p=239)

When you're driving you either pull over and slow down (if it's safe to do
so); or you keep driving at a safe speed and pull over when it's safe to do
so.

If you're at a traffic light you can either try to move to the side without
crossing the line; or you can stay where you are and allow the emergency
vehicle to sort it out; or you can cross the line if a police officer directs
you to do so (and blue lights is not a direction).

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namplaa
As far as I know in the Netherlands you get aside or stop when you see the
strobe and hear the siren, to let an emergency vehicle pass, it is also
allowed to run a red light.

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magoon
This sounds like an overly-expensive implementation of the simple strobe-based
signals used in the U.S. at nearly every intersection I've been through.

~~~
Menge
The old ones work by turning all lights red which is great for a low density
and organized traffic system and make it non-beneficial to hack them unless
you are immune to tickets.

If there is traffic crowding and narrow lanes or lane sharing then the
ambulance needs the drivers in front of it to also realize they have right of
way and the obligation to continue moving out of the way.

This is a common problem in older US/European cities where the streets have
not kept up with capacity and are not as wide as would be required by current
rules.

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EugeneOZ
Great idea! I think it worth to be implemented everywhere.

~~~
JshWright
Similar systems are in widespread use around the world.

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EugeneOZ
Cool, didn't know it. Not in wild Russia:)

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Aoyagi
Eh? Trams and buses in Czech Republic have been using this for years.

