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Author Topic: Timers on Traffic Signals  (Read 8079 times)

myosh_tino

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Re: Timers on Traffic Signals
« Reply #25 on: May 04, 2012, 11:52:01 PM »

Bulky, at many intersections the timers hit zero and no light change because the loop sensors are still tripped. This is common in SoCal. Countdown timers wouldn't work here because most of the signals here are fully actuated.

If the light relies on traffic detection, then the timer would be blank until the 10 seconds when the light WILL change.

The only thing that will alter it is an emergency vehicle or power failure. 
That's still not right.  If someone triggers the pedestrian signal, then there's a set minimum time the light will remain green to allow the person to cross the street.  When countdown timers and detection loops are both used, a signal will remain green for *at least* the amount of time on the countdown timer but the signal may stay green if additional traffic is detected by the loops.
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Re: Timers on Traffic Signals
« Reply #26 on: May 05, 2012, 10:13:09 AM »

The countdown would only initiate once the light starts ignoring additional traffic and pedestrians or there's no activity in the other directions. 

The detection loops are mainly used to cycle the light faster if there's no traffic.  If there's heavy traffic, they're on a timer.
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Re: Timers on Traffic Signals
« Reply #27 on: May 05, 2012, 12:52:49 PM »

In Wichita, I can think a few intersections where stoplights operate on timers, yet still don't change colors when the ped countdown hits zero.  I actually get annoyed while driving, because I use the ped countdown to tell me if I should slow down or not (expecting a red or green light upon arriving at the intersection);  I brake, preparing to stop, and then the light is still green.  D'oh!  If only I could remember excatly which intersections are like that every time I drive.
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Re: Timers on Traffic Signals
« Reply #28 on: May 06, 2012, 02:31:25 AM »

KEK, what if someone trips the "10-second" countdown you mention and then decides to make a right on red? The countdown clock goes blank?
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Re: Timers on Traffic Signals
« Reply #29 on: May 06, 2012, 07:47:01 AM »

KEK, what if someone trips the "10-second" countdown you mention and then decides to make a right on red? The countdown clock goes blank?

The light would commit to the 10 second countdown.  It would ignore pedestrian requests and traffic from other directions. 
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Re: Timers on Traffic Signals
« Reply #30 on: May 06, 2012, 04:12:45 PM »

KEK, what if someone trips the "10-second" countdown you mention and then decides to make a right on red? The countdown clock goes blank?

The light would commit to the 10 second countdown.  It would ignore pedestrian requests and traffic from other directions. 
Ideally, when it gets to 0 and the call has disappeared, the signal should reset without ever cycling through. I've also seen the peds stay on DW while the through light stays green until the next call.
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Re: Timers on Traffic Signals
« Reply #31 on: May 06, 2012, 04:58:38 PM »

The only way red or green countdowns for vehicles will work is if the signal runs fixed time settings, as the time to the beginning or end of a phase is always known. If any type of vehicle detection is used and the signal is in an actuated mode, the green or red settings vary dynamically within the phase depending on vehicle arrivals. Once the detectors stop sensing the presence of vehicles there is usually less than 6 seconds before the light changes (depending on travel speed and spacing of upstream detection--could be more but is frequently less). A vehicle countdown at this point is not really useful.

There is also the matter of drivers speeding up to make the light, or jumping the gun on a changing signal. I believe this was the main concern FHWA had in not allowing these displays, but the operational aspect of green extension in signal controllers is what makes the countdown less reliable.

The countdown would only initiate once the light starts ignoring additional traffic and pedestrians or there's no activity in the other directions. 

The detection loops are mainly used to cycle the light faster if there's no traffic.  If there's heavy traffic, they're on a timer.

If there's heavy traffic and detection is used, the light isn't necessarily on a "timer" but it's more likely that the green time reaches the maximum green setting in the controller and is forced to change phases. This is one possibility where a countdown might work, but again cannot be reliably predicted because of random traffic arrivals.
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Re: Timers on Traffic Signals
« Reply #32 on: May 07, 2012, 09:44:00 AM »

There are a number of them around here that reach 0 and the light doesn't immediately turn yellow. Several of those involve a lagging left-turn cycle, but not all of them. Some of them just seem to be random exceptions.
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Re: Timers on Traffic Signals
« Reply #33 on: May 08, 2012, 02:56:27 PM »

I like the large timers especially the one in the 2nd pic since theyre more geared for the driver to look at.
In Los Angeles ALL the lights have timers now. They're on the crosswalks but they always go no matter if someone crossed the street or not, generally lasting from 8-30 seconds preceded by the Walk symbol which usually will last an aditional 8-10 seconds, sometimes a bit more but not usually. And most of the suburbs have them too. The only city that I rarely see them in is Glendale, and then up a bit in LA County in the cities of Lancaster & Palmdale, however those 2 cities seem to be getting counters now as they replace old light setups.

The Phoenix area has these, too.
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Re: Timers on Traffic Signals
« Reply #34 on: May 08, 2012, 03:04:40 PM »

Not always.  Many of the signals in the San Jose area have countdown pedestrian timers but not all will change when the timer reaches 0.  This is because the signals also rely on detector loops in the pavement that tells the controller to keep the light green to allow additional traffic to pass through the intersection.

does the opposite exist?  i.e. a light turning yellow, then red, while the pedestrian counter keeps going?

the only way I could imagine this is if there were a segue into an all-pedestrian phase, but I cannot think of a situation where it would be good design to do this.
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myosh_tino

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Re: Timers on Traffic Signals
« Reply #35 on: May 08, 2012, 03:21:18 PM »

Not always.  Many of the signals in the San Jose area have countdown pedestrian timers but not all will change when the timer reaches 0.  This is because the signals also rely on detector loops in the pavement that tells the controller to keep the light green to allow additional traffic to pass through the intersection.

does the opposite exist?  i.e. a light turning yellow, then red, while the pedestrian counter keeps going?

the only way I could imagine this is if there were a segue into an all-pedestrian phase, but I cannot think of a situation where it would be good design to do this.
I have not seen a pedestrian signal behave like that but the only way one would exist is if, as you said, an all-pedestrian phase were coming up.
« Last Edit: May 08, 2012, 03:23:59 PM by myosh_tino »
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Re: Timers on Traffic Signals
« Reply #36 on: May 08, 2012, 03:24:54 PM »

I have not seen a pedestrian signal behave like that but the only way one would exist is if, as you said, an all-pedestrian phase were coming up.

I would say it is in fact not just a bad idea, but a terrible one, given that drivers use the pedestrian countdown to give themselves a worst case timing on when the green goes away.  a "surprise yellow" could be disastrous.
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myosh_tino

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Re: Timers on Traffic Signals
« Reply #37 on: May 08, 2012, 03:33:33 PM »

I have not seen a pedestrian signal behave like that but the only way one would exist is if, as you said, an all-pedestrian phase were coming up.

I would say it is in fact not just a bad idea, but a terrible one, given that drivers use the pedestrian countdown to give themselves a worst case timing on when the green goes away.  a "surprise yellow" could be disastrous.
What is you general opinion on an all-pedestrian phase?  Thinking about how traffic flows (or doesn't) in San Francisco, I'm wondering if adding an all-pedestrian phase would improve traffic flow by allowing cars turning right to not have to worry about pedestrians in the crosswalk.
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Re: Timers on Traffic Signals
« Reply #38 on: May 08, 2012, 03:42:56 PM »

What is you general opinion on an all-pedestrian phase?  Thinking about how traffic flows (or doesn't) in San Francisco, I'm wondering if adding an all-pedestrian phase would improve traffic flow by allowing cars turning right to not have to worry about pedestrians in the crosswalk.

I haven't had all that much experience with it.

in Los Angeles the pedestrian flow can get really bad for turning traffic.  since LA is installing a lot of protected lefts, I would imagine the solution would be to install corresponding protected rights as well.  i.e if eastbound is turning northbound, then at the same time southbound could be allowed to turn westbound.

but since SF doesn't seem to be as universally in the protected-left business, that might not be the solution there.  hell, half of SF's traffic lights are side-mounted, so not only would you need new signals for protected left, but you'd need new mast arms!
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Re: Timers on Traffic Signals
« Reply #39 on: May 08, 2012, 03:57:34 PM »

I have not seen a pedestrian signal behave like that but the only way one would exist is if, as you said, an all-pedestrian phase were coming up.

I would say it is in fact not just a bad idea, but a terrible one, given that drivers use the pedestrian countdown to give themselves a worst case timing on when the green goes away.  a "surprise yellow" could be disastrous.
What is you general opinion on an all-pedestrian phase?  Thinking about how traffic flows (or doesn't) in San Francisco, I'm wondering if adding an all-pedestrian phase would improve traffic flow by allowing cars turning right to not have to worry about pedestrians in the crosswalk.

DC has one intersection with an all-pedestrian phase, the intersection of 7th & H Streets NW near the Verizon Center and Chinatown. An entrance to a subway stop is located on the southeast corner of the intersection and it's a high-pedestrian area pretty much most of the time due to a high concentration of restaurants and bars. When I'm a pedestrian I like the all-way phasing.

But I never drive through that intersection if I can avoid it because of the way DC implemented it. A normal "Barnes Dance" phasing allows crossing only during the all-way phase. That way drivers are free to turn right or left, or go straight, without encountering pedestrians (who in return get a shorter crossing because they can go diagonally and cross just once instead of twice). But DC decided that most pedestrians in the DC area cannot be trusted to wait their turn before crossing on a "Walk" signal (that's probably true because 95% of them think they can walk whenever and wherever they want) and that if the all-way pedestrian phase were the only time at which a "Walk" signal were displayed, pedestrians would get tired of waiting and would walk against the light (probably a valid assumption because they do that everywhere else). So instead of prohibiting crossing outside of the "all-way pedestrian" phase, DC instead prohibited motorists from making any turns (right or left) at that intersection. The theory is that by prohibiting turns you eliminate the conflict between turning drivers and pedestrians, and you also eliminate the delays when a turning car blocks the way for other cars. Problem is, many drivers ignore the no-turns restriction (and many don't seem aware of it at all because the signs aren't really prominent enough in that very busy area), and I suppose nobody should really be surprised at this because H Street is a fairly important cross-town route ever since Bill Clinton let the Secret Service close a section of Pennsylvania Avenue in 1995.
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Re: Timers on Traffic Signals
« Reply #40 on: May 08, 2012, 04:03:03 PM »


But I never drive through that intersection if I can avoid it because of the way DC implemented it.
[snip]

are you saying there are only three phases?

north-south, no turns
east-west, no turns
pedestrians

rinse and repeat?
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Re: Timers on Traffic Signals
« Reply #41 on: May 08, 2012, 04:18:47 PM »


But I never drive through that intersection if I can avoid it because of the way DC implemented it.
[snip]

are you saying there are only three phases?

north-south, no turns
east-west, no turns
pedestrians

rinse and repeat?


Sort of, with a clarification to underscore how the pedestrian signals work. 7th Street runs north/south and H Street runs east/west. So this is what it does:

(a) 7th Street traffic has a green light and pedestrians crossing H Street get "Walk" signals (for conventional straight-across crossing only). No turns allowed.

(b) H Street traffic has a green light and pedestrians crossing 7th Street get "Walk" signals (again for straight-across crossing only). No turns allowed.

(c) All-way red for drivers and the pedestrians get "Walk" signals for both straight-across and diagonal crossing. No turns allowed.

After (c) it goes back to (a) again.

Turns are occasionally allowed when one of the streets is closed, of course; 7th is sometimes closed south of H after a game or a concert and H is periodically closed east of 7th if there's some sort of Chinese festival going on (the name "Chinatown" isn't too accurate anymore and "Chinablock" might be more accurate to refer to that one block).
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Re: Timers on Traffic Signals
« Reply #42 on: May 08, 2012, 04:24:10 PM »

that just sounds like silly design overall.

San Francisco also has some intersections with particular turns prohibited.  Park Presidio at Fulton comes to mind.  In order to take a left turn, one has to turn right onto a small anonymous residential street, turn left onto another, and then turn left onto Fulton - a completely unprotected left turning onto four lanes of boulevard traffic.

this is pretty badly signed, so you just imagine your GPS is smoking something powerful when it suggests that ... but that is, indeed, the correct way to do things.
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Re: Timers on Traffic Signals
« Reply #43 on: May 08, 2012, 05:01:30 PM »

San Francisco also has some intersections with particular turns prohibited.  Park Presidio at Fulton comes to mind.  In order to take a left turn, one has to turn right onto a small anonymous residential street, turn left onto another, and then turn left onto Fulton - a completely unprotected left turning onto four lanes of boulevard traffic.

this is pretty badly signed, so you just imagine your GPS is smoking something powerful when it suggests that ... but that is, indeed, the correct way to do things.
Totally jughandular, man.
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Re: Timers on Traffic Signals
« Reply #44 on: May 08, 2012, 05:06:42 PM »


Totally jughandular, man.

does that count as a jughandle?

http://en.wikipedia.org/wiki/Jughandle

there are three types mentioned there, and none require three explicit turns.  at least one of the turns is smoothed out (Type A) into a ramp, or both are (Type B) or the jughandle is in reverse with a single ramp (Type C).
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Re: Timers on Traffic Signals
« Reply #45 on: May 08, 2012, 05:22:26 PM »

I'd count it, since it simply replaces the ramps with existing streets. No different from an interchange that uses streets.
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Re: Timers on Traffic Signals
« Reply #46 on: May 08, 2012, 05:42:02 PM »

that just sounds like silly design overall.

San Francisco also has some intersections with particular turns prohibited.  Park Presidio at Fulton comes to mind.  In order to take a left turn, one has to turn right onto a small anonymous residential street, turn left onto another, and then turn left onto Fulton - a completely unprotected left turning onto four lanes of boulevard traffic.

this is pretty badly signed, so you just imagine your GPS is smoking something powerful when it suggests that ... but that is, indeed, the correct way to do things.

I understand prohibiting some turns, particularly left turns in an urban area where there are no turn lanes. I probably should have mentioned that the 7th & H intersection I mentioned earlier is of that sort (no turn lanes for either right or left turns) and so banning left turns even with a traditional "Barnes Dance" configuration would have made sense. But banning right turns is a nuisance.

Come to think of it, I wonder how many people seeking to turn there are being guided by sat-navs that were programmed prior to the "No Turns" restriction, which only went up within the past two or three years.
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Re: Timers on Traffic Signals
« Reply #47 on: May 08, 2012, 07:03:46 PM »

Not always.  Many of the signals in the San Jose area have countdown pedestrian timers but not all will change when the timer reaches 0.  This is because the signals also rely on detector loops in the pavement that tells the controller to keep the light green to allow additional traffic to pass through the intersection.

does the opposite exist?  i.e. a light turning yellow, then red, while the pedestrian counter keeps going?

the only way I could imagine this is if there were a segue into an all-pedestrian phase, but I cannot think of a situation where it would be good design to do this.

I've seen a signal that had the WALK signal on during red lights and DON'T WALK during green lights.  But, then, that was just a signal not working properly.  :-/
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Re: Timers on Traffic Signals
« Reply #48 on: May 08, 2012, 07:32:48 PM »

Not always.  Many of the signals in the San Jose area have countdown pedestrian timers but not all will change when the timer reaches 0.  This is because the signals also rely on detector loops in the pavement that tells the controller to keep the light green to allow additional traffic to pass through the intersection.

does the opposite exist?  i.e. a light turning yellow, then red, while the pedestrian counter keeps going?

the only way I could imagine this is if there were a segue into an all-pedestrian phase, but I cannot think of a situation where it would be good design to do this.
I've seen older counters reach 0 at the red light, but that's been written out of the MUTCD and agencies are now converting to the new standard. While on the topic of the MUTCD, I'll just point out that drivers are explicitly not supposed to rely on pedestrian timers. I know they do anyway, but my point is that design should not account for that.
« Last Edit: May 08, 2012, 07:35:07 PM by Steve »
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Re: Timers on Traffic Signals
« Reply #49 on: May 08, 2012, 07:39:15 PM »

While on the topic of the MUTCD, I'll just point out that drivers are explicitly not supposed to rely on pedestrian timers. I know they do anyway, but my point is that design should not account for that.

how does the general driving populace know that?  countdown timers certainly weren't covered when I took driver ed, so I'd be tempted to go with my intuition...
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