AARoads Forum

National Boards => General Highway Talk => Traffic Control => Topic started by: thenetwork on November 24, 2009, 06:53:02 PM

Title: Red to Yellow to Green Changing Lights...
Post by: thenetwork on November 24, 2009, 06:53:02 PM
There has been two times in my lifetime (so far) when I have seen a single-light intersection run a sequence that started at Red, then change to solid yellow for all directions, then to Green or Red, depending on what they had prior to the all-yellow.

The first time (20+ years ago) was at an intersection on SR-237 in Strongsville, Ohio.  That sequence did not last long until it was "changed".

And the other time was as recently as 10-15 years ago on (or just off of) SR-7 in a small riverside town in Southeast Ohio.  Never got back there to see if it still runs like that.

Has anybody else seen an intersection where the signal(s) run the full Green-Yellow-Red sequence both forward and backward?  I know it was not uncommon to see 50+ years ago, but to see it still today is,...freaky!



Title: Re: Red to Yellow to Green Changing Lights...
Post by: US71 on November 24, 2009, 07:59:09 PM
There has been two times in my lifetime (so far) when I have seen a single-light intersection run a sequence that started at Red, then change to solid yellow for all directions, then to Green or Red, depending on what they had prior to the all-yellow.

The first time (20+ years ago) was at an intersection on SR-237 in Strongsville, Ohio.  That sequence did not last long until it was "changed".

And the other time was as recently as 10-15 years ago on (or just off of) SR-7 in a small riverside town in Southeast Ohio.  Never got back there to see if it still runs like that.

Has anybody else seen an intersection where the signal(s) run the full Green-Yellow-Red sequence both forward and backward?  I know it was not uncommon to see 50+ years ago, but to see it still today is,...freaky!


I've seen it several times in Oklahoma.
Title: Re: Red to Yellow to Green Changing Lights...
Post by: deathtopumpkins on November 24, 2009, 08:09:57 PM
I saw a signal recently in Virginia Beach (can't recall where though... possibly on First Colonial?) that flashed yellow three times before changing to green for through traffic... I found that very helpful.
Title: Re: Red to Yellow to Green Changing Lights...
Post by: agentsteel53 on November 24, 2009, 10:51:20 PM
it is all over the place in Europe, except there the intermediate phase between red and green is having both red and yellow lights turned on.

it is mainly for the benefit of stick-shift drivers, who can put the clutch down and the car back in gear just in time for the light to turn green.

if I recall, there is an extra phase in Mexico as well, but I do not recall what it is.  I know, there, when the light is about to turn red, the green light flashes for about 3 seconds before it turns yellow because the yellow is much shorter there than in the US - drivers know to try to run flashing green, but stop on yellow.
Title: Re: Red to Yellow to Green Changing Lights...
Post by: Alex on November 25, 2009, 04:55:22 PM
I have seen this signal sequence before, but cannot remember specifically where or when, though the first thing that comes to mind are traffic lights throughout Allentown, Pennsylvania when I was there in 1994. I do have some video from that trip, and know for sure that some of the signals cycled in a way that in between phases, all lens would go dark momentarily. I.e. green - off - yellow - off - red...
Title: Re: Red to Yellow to Green Changing Lights...
Post by: Alps on November 25, 2009, 06:00:20 PM
I have seen this signal sequence before, but cannot remember specifically where or when, though the first thing that comes to mind are traffic lights throughout Allentown, Pennsylvania when I was there in 1994. I do have some video from that trip, and know for sure that some of the signals cycled in a way that in between phases, all lens would go dark momentarily. I.e. green - off - yellow - off - red...

Old signals in many places do that, or else have overlap.  An old set on Bloomfield Ave. in Clifton by NJ 3 used to go yellow-red for a full second.  By the time I had a digital camera, it was gone.  Old signals in Poughkeepsie and Albany, among other upstate NY cities, go blank between phases for countable time.
Title: Re: Red to Yellow to Green Changing Lights...
Post by: Chris on November 26, 2009, 12:50:31 PM
Every traffic signal in Germany has this feature. Other countries in Europe as well, but not all countries (can't remember France having it).
Title: Re: Red to Yellow to Green Changing Lights...
Post by: Mr_Northside on November 27, 2009, 10:00:48 AM
The yellow-before-green thing was one of the first things that I really noticed when I was in the U.K. that I wasn't expecting.  (Obviously, I knew about the left-hand driving and their extensive use of roundabouts.)
Title: Re: Red to Yellow to Green Changing Lights...
Post by: english si on November 27, 2009, 12:58:48 PM
it is mainly for the benefit of stick-shift drivers, who can put the clutch down and the car back in gear just in time for the light to turn green.
I think you mean the opposite of putting the clutch down - foot on clutch means that the car isn't in gear, because the clutch is engaged.

France's traffic lights just go red-green-yellow-red. UK is red-red+amber-green-amber-red, though some pedestrian crossings are exceptions - a flashing amber phase between red and green, which is pretty much 'yield to those still crossing'.
Title: Re: Red to Yellow to Green Changing Lights...
Post by: njroadhorse on November 27, 2009, 01:14:33 PM
British traffic signals have a red-yellow phase, but I do not remember if its before or after red.
Title: Re: Red to Yellow to Green Changing Lights...
Post by: Truvelo on November 27, 2009, 01:36:45 PM
British traffic signals have a red-yellow phase, but I do not remember if its before or after red.

It's after the red. This image shows the order.

(http://upload.wikimedia.org/wikipedia/commons/thumb/2/24/Traffic_lights_4_states.svg/200px-Traffic_lights_4_states.svg.png)
Title: Re: Red to Yellow to Green Changing Lights...
Post by: J N Winkler on November 27, 2009, 01:46:39 PM
Red and yellow on at the same time is formally known as "starting amber" in Britain.  One interesting design option, which (fortunately) is rarely exercised, is to have starting amber overlap with yellow on the conflicting aspect.  Starting amber still means "stop" but it is not uncommon to start off before green.

Pelican crossings have the flashing yellow ("yield to pedestrians still crossing") Simon describes.  Normally the green man pedestrian aspect starts flashing before the vehicle signal shows flashing yellow.  A newer type of pedestrian crossing, the puffin, has signal phasing similar to road junction signals, including starting amber.
Title: Re: Red to Yellow to Green Changing Lights...
Post by: agentsteel53 on November 27, 2009, 01:48:36 PM
have starting amber overlap with yellow on the conflicting aspect. 


you mean red-yellow could occur both before red, and before green?  Bloody 'ell!
Title: Re: Red to Yellow to Green Changing Lights...
Post by: agentsteel53 on November 27, 2009, 01:49:22 PM


(http://upload.wikimedia.org/wikipedia/commons/thumb/2/24/Traffic_lights_4_states.svg/200px-Traffic_lights_4_states.svg.png)

that is how it is done on the continent as well, for reasons mentioned before.  "clutch down, car into gear, prepare to accelerate"
Title: Re: Red to Yellow to Green Changing Lights...
Post by: J N Winkler on November 27, 2009, 01:59:16 PM
you mean red-yellow could occur both before red, and before green?  Bloody 'ell!

Yup.  Minimum yellow time is 3 seconds, and starting amber is (IIRC) 1 second, so if you double up on starting amber and yellow on the conflicting approach, you can get intergreen time down to 3 seconds.  Not a lot of margin for error!
Title: Re: Red to Yellow to Green Changing Lights...
Post by: agentsteel53 on November 27, 2009, 02:06:55 PM
wait, now I am confused.  Walk me through the cycle please?
Title: Re: Red to Yellow to Green Changing Lights...
Post by: J N Winkler on November 27, 2009, 02:13:46 PM
I was relying on memory and it turns out I was wrong.  Starting amber is 2 seconds, yellow is 3 seconds, and the overlap of the two is limited to 1 second, so minimum intergreen time is 4 seconds.  From the horse's mouth:

Quote from: Design Manual for Roads and Bridges
5.6 Intergreen Period

The period between the end of the green display on one stage and the start of the green display on the next stage is
known as the intergreen period. It comprises an amber display, the red + amber display and may also contain a period
when the red signals are shown to all approaches simultaneously. The minimum time for this period is four seconds,
when the amber and red + amber periods overlap by one second. With a five second intergreen the amber and red +
amber periods occur consecutively. Any period over five seconds will include a period where red signals are shown to
all approaches simultaneously.

You can get the full skinny from TA 16/81 (http://www.standardsforhighways.co.uk/dmrb/vol8/section1/ta1681.pdf) (DMRB 8.1.1).
Title: Re: Red to Yellow to Green Changing Lights...
Post by: agentsteel53 on November 27, 2009, 02:44:02 PM
so the light never actually turns to red-only?
Title: Re: Red to Yellow to Green Changing Lights...
Post by: J N Winkler on November 27, 2009, 03:26:55 PM
Actually, two signals are involved--one signal and another signal on a conflicting approach.  In order for the first signal to get green, the other signal must be red.  Four seconds of intergreen time (the minimum) allows the first second of starting amber (which precedes green) for the first signal to overlap the last second of yellow time (which precedes red) for the conflicting signal.  For intergreen times of up to five seconds, there is never a time when both signals are showing red.  For intergreen times of more than five seconds, there is all-red time because the yellow phase for the conflicting signal ends (and the signal goes red) before the first signal goes from red to starting amber.