Pedestrian Countdown Signals

[jeffandnicole]

Delaware has some intersections where the flashing hand and countdown timer continues into the yellow phase. There are, I believe, 5 permitted rules as to how walk/don't walk signals operate; I believe I've seen 3 or 4 of them in use in DE.

[tradephoric]

Pedestrians are allowed to start their crossing at any point during the steady WALKING PERSON but shall not start their crossing during the flashing UPRAISED HAND.  With this in mind, I don't understand the logic of the following MUTCD guidance:

14   The total of the walk interval and pedestrian clearance time should be sufficient to allow a pedestrian crossing in the crosswalk who left the pedestrian detector (or, if no pedestrian detector is present, a location 6 feet from the face of the curb or from the edge of the pavement) at the beginning of the WALKING PERSON (symbolizing WALK) signal indication to travel at a walking speed of 3 feet per second to the far side of the traveled way being crossed or to the median if a two-stage pedestrian crossing sequence is used.  Any additional time that is required to satisfy the conditions of this paragraph should be added to the walk interval.

This guidance seems ambiguous since pedestrians have been taught that they can start their crossing during the steady WALKING PERSON (whether it be near the beginning, middle, or end of the walking person indication).  Since it can't be assumed that a pedestrian is going to start to cross at the beginning of the WALKING PERSON, what's the point of Paragraph 14? 

[Alps]

Pedestrians are allowed to start their crossing at any point during the steady WALKING PERSON but shall not start their crossing during the flashing UPRAISED HAND.  With this in mind, I don't understand the logic of the following MUTCD guidance:

14   The total of the walk interval and pedestrian clearance time should be sufficient to allow a pedestrian crossing in the crosswalk who left the pedestrian detector (or, if no pedestrian detector is present, a location 6 feet from the face of the curb or from the edge of the pavement) at the beginning of the WALKING PERSON (symbolizing WALK) signal indication to travel at a walking speed of 3 feet per second to the far side of the traveled way being crossed or to the median if a two-stage pedestrian crossing sequence is used.  Any additional time that is required to satisfy the conditions of this paragraph should be added to the walk interval.

This guidance seems ambiguous since pedestrians have been taught that they can start their crossing during the steady WALKING PERSON (whether it be near the beginning, middle, or end of the walking person indication).  Since it can't be assumed that a pedestrian is going to start to cross at the beginning of the WALKING PERSON, what's the point of Paragraph 14? 

Because the more time you allow for pedestrians, the longer your minimum green time has to be. They're trying to mitigate that as much as possible by saying that you only have to accommodate the slowest pedestrians who start on the beginning of the signal. Peds who are that slow may actually wait to cross a street if they're not sure they can make it.

[tradephoric]

I don't dispute what Steve is saying.  However, many slow moving pedestrians aren't going to wait to cross at the very beginning of the walk.  Ideally, you would want a slow moving pedestrian to start their crossing as soon as the walk comes up to give them as much time as possible to safely cross.  Why then would the last line of Paragraph 14 read this?

Any additional time that is required to satisfy the conditions of this paragraph should be added to the walk interval.

Shouldn't any additional time be added to the pedestrian change interval (flashing don't walk) as opposed to the walk interval?  As an example, assume a 140 ft crossing with a standard 7 second walk and a pushbutton 10 feet from the curb.

Walk:  7 seconds
Ped clearance time: 140 ft / (3.5 ft/sec) = 40 seconds
Guidance 14 test:  (140 ft + 10 ft) / (3 ft/sec) = 50 seconds

Following the guidance from paragraph 14, you would have to increase the walk to 10 seconds (10 second walk + 40 second ped clearance >= 50 second paragraph 14 guidance).  Wouldn't it make more sense to have a 7 second walk and a 43 second ped clearance as opposed to a 10 second walk and a 40 second ped clearance?  The flashing don't walk starting 3 seconds earlier may prevent a slow moving pedestrian from starting their crossing where they won't have enough time to safely cross.

[tradephoric]

Another issue I have with the MUTCD standards is that there is no upper limit to how high the buffer interval can be.  Sure, it says you need at least a 3 second buffer but an agency can use a 12 second buffer for situations where there is a boulevard with a trail green (6 sec trail green + 4 sec yellow + 2 sec all red).  Suppose a pedestrian crossing at the trail green intersection is 70 ft long and requires a 20 second pedestrian clearance time (70 ft / 3.5 = 20 sec).  The agency subtracts the 12 second buffer from the 20 second pedestrian clearance time to gets an 8 second pedestrian change interval (FDW).  This is in accordance to the MUTCD standards.  A pedestrian who steps off the curb just as the countdown timer begins would have to average 8.75 ft/sec to make it across by the time the countdown timer reaches zero (the pedestrian would still have a 12 second buffer to safely complete their crossing but how are they to know that?).  This may be an extreme example but the MUTCD standards allow the pedestrian change interval (FDW) to be a small percentage of the total pedestrian clearance time.  There is little to no guidance in how to deal with a situation like this.

*Note: FDW = Flashing Don't Walk

[Brandon]

^^ I've seen pedestrian signals in Chicago that have a short walk cycle (maybe 5 seconds) followed by at least 25 seconds of a flashing don't walk cycle with the countdown.  Then the signal turns yellow when the solid don't walk cycle comes on.

[Alps]

I don't dispute what Steve is saying.  However, many slow moving pedestrians aren't going to wait to cross at the very beginning of the walk.  Ideally, you would want a slow moving pedestrian to start their crossing as soon as the walk comes up to give them as much time as possible to safely cross.  Why then would the last line of Paragraph 14 read this?

Any additional time that is required to satisfy the conditions of this paragraph should be added to the walk interval.

Shouldn't any additional time be added to the pedestrian change interval (flashing don't walk) as opposed to the walk interval?  As an example, assume a 140 ft crossing with a standard 7 second walk and a pushbutton 10 feet from the curb.

Walk:  7 seconds
Ped clearance time: 140 ft / (3.5 ft/sec) = 40 seconds
Guidance 14 test:  (140 ft + 10 ft) / (3 ft/sec) = 50 seconds

Following the guidance from paragraph 14, you would have to increase the walk to 10 seconds (10 second walk + 40 second ped clearance >= 50 second paragraph 14 guidance).  Wouldn't it make more sense to have a 7 second walk and a 43 second ped clearance as opposed to a 10 second walk and a 40 second ped clearance?  The flashing don't walk starting 3 seconds earlier may prevent a slow moving pedestrian from starting their crossing where they won't have enough time to safely cross.

Because clearance time is based on the average person - which used to be 4 ft/s, but was downgraded due to our aging population. You can't design to the worst case - imagine what our curves and speed limits would look like if they were based on 18 wheelers!

[NE2]

You can't design to the worst case - imagine what our curves and speed limits would look like if they were based on 18 wheelers!

You do design to the worst case: bridges must be able to support trucks of the maximum weight, for example. More relevant to the topic of traffic signals, yellow time should (but may not always) take into account the lesser braking ability of trucks.

[Alps]

You can't design to the worst case - imagine what our curves and speed limits would look like if they were based on 18 wheelers!

You do design to the worst case: bridges must be able to support trucks of the maximum weight, for example. More relevant to the topic of traffic signals, yellow time should (but may not always) take into account the lesser braking ability of trucks.

Actually, trucks must have enough axles to distribute their load for bridges, based on the maximum design axle load used in design. Also, yellow lights are designed 1 second per 10 mph approach speed. A truck traveling 60 mph will be able to go 528 feet in 6 seconds. According to Utah, it takes 525 feet to stop from 65 mph. So... I guess it works.

[tradephoric]

I don't dispute what Steve is saying.  However, many slow moving pedestrians aren't going to wait to cross at the very beginning of the walk.  Ideally, you would want a slow moving pedestrian to start their crossing as soon as the walk comes up to give them as much time as possible to safely cross.  Why then would the last line of Paragraph 14 read this?

Any additional time that is required to satisfy the conditions of this paragraph should be added to the walk interval.

Shouldn't any additional time be added to the pedestrian change interval (flashing don't walk) as opposed to the walk interval?  As an example, assume a 140 ft crossing with a standard 7 second walk and a pushbutton 10 feet from the curb.

Walk:  7 seconds
Ped clearance time: 140 ft / (3.5 ft/sec) = 40 seconds
Guidance 14 test:  (140 ft + 10 ft) / (3 ft/sec) = 50 seconds

Following the guidance from paragraph 14, you would have to increase the walk to 10 seconds (10 second walk + 40 second ped clearance >= 50 second paragraph 14 guidance).  Wouldn't it make more sense to have a 7 second walk and a 43 second ped clearance as opposed to a 10 second walk and a 40 second ped clearance?  The flashing don't walk starting 3 seconds earlier may prevent a slow moving pedestrian from starting their crossing where they won't have enough time to safely cross.

Because clearance time is based on the average person - which used to be 4 ft/s, but was downgraded due to our aging population. You can't design to the worst case - imagine what our curves and speed limits would look like if they were based on 18 wheelers!

Here's a 210 ft crosswalk in Wylie, Texas (pushbutton 15 ft from edge of curb):


If you were calculating the pedestrian times for the crosswalk above, which option would you want to follow?

Option A: 

14   The total of the walk interval and pedestrian clearance time should be sufficient to allow a pedestrian crossing in the crosswalk who left the pedestrian detector (or, if no pedestrian detector is present, a location 6 feet from the face of the curb or from the edge of the pavement) at the beginning of the WALKING PERSON (symbolizing WALK) signal indication to travel at a walking speed of 3 feet per second to the far side of the traveled way being crossed or to the median if a two-stage pedestrian crossing sequence is used.  Any additional time that is required to satisfy the conditions of this paragraph should be added to the walk interval.

Walk interval       = 15 sec  Additional time added to the walk interval.
Ped Clearance     = 60 sec 
Walk + Clearance = 75 sec

A pedestrian that starts to cross at the end of the walk interval would need to average 3.5 fps (60 sec * 3.5 fps = 210 ft).

Option B:

14   The total of the walk interval and pedestrian clearance time should be sufficient to allow a pedestrian crossing in the crosswalk who left the pedestrian detector (or, if no pedestrian detector is present, a location 6 feet from the face of the curb or from the edge of the pavement) at the beginning of the WALKING PERSON (symbolizing WALK) signal indication to travel at a walking speed of 3 feet per second to the far side of the traveled way being crossed or to the median if a two-stage pedestrian crossing sequence is used.  Any additional time that is required to satisfy the conditions of this paragraph should be added to the pedestrian clearance interval.

Walk interval       = 7 sec
Ped Clearance     = 68 sec  Additional time added to the ped clearance.
Walk + Clearance = 75 sec

A pedestrian that starts to cross at the end of the walk interval would need to average 3.09 fps (68 sec * 3.09 fps = 210 ft).

[realjd]

The MUTCD doesn't allow the numbers turning on when walking starts?

Correct. 

4E.07  2009 MUTCD

05 The display of the number of remaining seconds shall begin only at the beginning of the pedestrian change interval (flashing UPRAISED HAND). After the countdown displays zero, the display shall remain dark until the beginning of the next countdown.

06 The countdown pedestrian signal shall display the number of seconds remaining until the termination of the pedestrian change interval (flashing UPRAISED HAND). Countdown displays shall not be used during the walk interval or during the red clearance interval of a concurrent vehicular phase.

I finally remembered where I see countdown timers with a walk signal: DC. The standard DC pedestrian cycle is walk with a countdown directly into a don't walk. They skip the flashing don't walk completely.

[tradephoric]

^^^ This is an old video but shows a countdown timer starting during the walk interval in Washington D.C.

[tradephoric]

Can anybody explain the logic of adding the extra time to the walk interval as opposed to the pedestrian clearance time when following the guidance of paragraph 14?  See reply #34.

[NE2]

Can anybody explain the logic of adding the extra time to the walk interval as opposed to the pedestrian clearance time when following the guidance of paragraph 14?  See reply #34.

How'd you like driving if the green was 10 seconds and the yellow was 40 seconds, and you couldn't legally enter on the yellow even if you knew you could make it across before red?

[jeffandnicole]

Can anybody explain the logic of adding the extra time to the walk interval as opposed to the pedestrian clearance time when following the guidance of paragraph 14?  See reply #34.

How'd you like driving if the green was 10 seconds and the yellow was 40 seconds, and you couldn't legally enter on the yellow even if you knew you could make it across before red?

That'll be yucky.

[roadfro]

Can anybody explain the logic of adding the extra time to the walk interval as opposed to the pedestrian clearance time when following the guidance of paragraph 14?  See reply #34.

The pedestrian clearance time (FDW) has already been lengthened by the change from 4 ft/s to 3.5 ft/s used to calculate it's duration, so why lengthen it further?


My hunch: The FDW is supposed to be set so that it is a fixed duration based on that walking assumed speed in the actual crossing (not a distance from the button or behind the curb). If this is applied universally, people can better judge their crossing movements based on personal experiences at other crossings of similar or differing distances. Already we see with countdown signals that some pedestrians will begin their crossing during the FDW countdown, as they have experience crossing such a distance with a certain amount of time left on the countdown--similarly, they know that by a certain point in the countdown for a given distance, they may not be able to make it across in time. If you start adding extra time to the FDW, based on a distance measurement (say the ped detectors are further away from the curb at an otherwise identical intersection), then pedestrian expectation can be disrupted because the FDW times vary.

[For example, I frequent a crossing on my campus going back and forth between offices. The FDW time is 14 seconds, but I know if I'm in a hurry I can step off the curb with 8 seconds to go and still make it across by the end of the countdown at my normal walking speed. Based on that, I have successfully judged my crossing at a different, unfamiliar intersection with the same number of lanes to cross, knowing how long it takes me to walk the same distance at my crossing by work.]

It may not be a big difference overall but it can lead to misjudging the crossing and people thinking that all FDW times are set deliberately long, which can induce further non-compliance with ped signals.

How'd you like driving if the green was 10 seconds and the yellow was 40 seconds, and you couldn't legally enter on the yellow even if you knew you could make it across before red?

And this.

[tradephoric]

To add to the analogy...

The deceleration rate of a Ferrari is going to be a lot quicker than the deceleration rate of an 18-wheeler.  Do agencies calculate the yellow change interval assuming that only Ferrari's are going to be in the dilemma zone when the light turns yellow?  The Ferrari driver could stop on a dime and manage a 2 second yellow but is forced to stop at a 5 second yellow light (even though the driver knows he could have made it had the yellow been delayed by 3 more seconds).

My bigger argument is that guidance 14 is unnecessary since there are no guarantees that a slow moving pedestrian is going to begin to cross at the beginning of the walk.  Pedestrians are allowed to cross at any point during the walk phase (beginning, middle, or end) regardless of their walking speed.  In addition, guidance already exists in the MUTCD that deals with pedestrians who walk slower than 3.5 feet per second:

10   Where pedestrians who walk slower than 3.5 feet per second, or pedestrians who use wheelchairs, routinely use the crosswalk, a walking speed of less than 3.5 feet per second should be considered in determining the pedestrian clearance time.

Two reasons why I believe paragraph 14 in the MUTCD is unnecessary:
Reason 1:  Paragraph 10 already already deals with slower moving pedestrians and any additional guidance becomes redundant.
Reason 2:  Pedestrians are taught to cross at any point during the walk interval, and the guidance of paragraph 14 isn't beneficial when a slow moving pedestrian starts to cross at the end of the walk phase.

My hunch: The FDW is supposed to be set so that it is a fixed duration based on that walking assumed speed in the actual crossing (not a distance from the button or behind the curb). If this is applied universally, people can better judge their crossing movements based on personal experiences at other crossings of similar or differing distances. Already we see with countdown signals that some pedestrians will begin their crossing during the FDW countdown, as they have experience crossing such a distance with a certain amount of time left on the countdown--similarly, they know that by a certain point in the countdown for a given distance, they may not be able to make it across in time. If you start adding extra time to the FDW, based on a distance measurement (say the ped detectors are further away from the curb at an otherwise identical intersection), then pedestrian expectation can be disrupted because the FDW times vary.

[For example, I frequent a crossing on my campus going back and forth between offices. The FDW time is 14 seconds, but I know if I'm in a hurry I can step off the curb with 8 seconds to go and still make it across by the end of the countdown at my normal walking speed. Based on that, I have successfully judged my crossing at a different, unfamiliar intersection with the same number of lanes to cross, knowing how long it takes me to walk the same distance at my crossing by work.]

It may not be a big difference overall but it can lead to misjudging the crossing and people thinking that all FDW times are set deliberately long, which can induce further non-compliance with ped signals.

This was an extremely good explanation!  Thank you roadfro.

[realjd]

The MUTCD doesn't allow the numbers turning on when walking starts?

Correct. 

4E.07  2009 MUTCD

05 The display of the number of remaining seconds shall begin only at the beginning of the pedestrian change interval (flashing UPRAISED HAND). After the countdown displays zero, the display shall remain dark until the beginning of the next countdown.

06 The countdown pedestrian signal shall display the number of seconds remaining until the termination of the pedestrian change interval (flashing UPRAISED HAND). Countdown displays shall not be used during the walk interval or during the red clearance interval of a concurrent vehicular phase.

I finally remembered where I see countdown timers with a walk signal: DC. The standard DC pedestrian cycle is walk with a countdown directly into a don't walk. They skip the flashing don't walk completely.

To update: DC does have a flashing hand phase on the countdown signals. It lasts as short as 2 seconds which is why I didn't notice it.

[tradephoric]

My hunch: The FDW is supposed to be set so that it is a fixed duration based on that walking assumed speed in the actual crossing (not a distance from the button or behind the curb). If this is applied universally, people can better judge their crossing movements based on personal experiences at other crossings of similar or differing distances. Already we see with countdown signals that some pedestrians will begin their crossing during the FDW countdown, as they have experience crossing such a distance with a certain amount of time left on the countdown--similarly, they know that by a certain point in the countdown for a given distance, they may not be able to make it across in time. If you start adding extra time to the FDW, based on a distance measurement (say the ped detectors are further away from the curb at an otherwise identical intersection), then pedestrian expectation can be disrupted because the FDW times vary.

I came up with one major flaw with your hunch.  Consider the following guidance:

  ***  The Buffer Interval, which shall always be provided and displayed, may be used to help satisfy the calculated pedestrian clearance time, or may begin after the calculated pedestrian clearance time has ended.

This means for two identical 70 ft crossings the FDW time could be very different.  An agency that uses the buffer interval to help satisfy the calculated pedestrian clearance time may choose a 14 second FDW (70 / 3.5 = 20 sec ped clearance — 6 sec. buffer = 14 seconds).  Another agency that doesn't use the buffer interval to satisfy the pedestrian clearance time may choose to use a 20 second FDW (70 / 3.5 = 20 second).  So for identical 70 ft crossing, one intersection may have a 14 second FDW time while another intersection just down the street has a 20 second FDW. 

Also, see Reply #29 which talks about how the MUTCD standards allow the pedestrian change interval (FDW) to be a small percentage of the total pedestrian clearance time.  I used a 6 second buffer in this example because many controllers are limited in when the FDW time terminates.  At least a 3 second buffer is required in the MUTCD but it's quite common to have longer buffers in practice.

[tradephoric]

Pedestrian refuge islands can split up a long pedestrian crossing into two shorter crossings which can improve intersection efficiency (a side-street can have shorter pedestrian clearance times and go to the main-street earlier).   The question is are pedestrian refuge islands really that much of a refuge for pedestrians?  Here is an example of a refuge island at an intersection in Tuscon, AZ:



The refuge island is so narrow that the pedestrian has few options to react to an out of control vehicle.  The pedestrian is unable to create a buffer zone between them and opposing traffic and it just seems like they are a sitting duck if something bad were to happen.   I like pedestrian refuge islands but feel like they need to be wide enough to give pedestrian a chance to escape from a dangerous situation (or allow them to wait farther back from the edge of the curb while waiting to cross).  This video came to mind when i saw that Tuscon pedestrian island.  WARNING: This video shows a serious accident involving a pedestrian:

[mrsman]

wow, what a crazy video.  Do you know anything about this intersection?  Where was it? Was the traffic light broken?

In a regular intersection, I would never aim to wait around in a ped island that is so narrow.  In some intersections here in DC, the traffic lights are offset and force one to wait on an island.  Fortunately, they aren't close to home or office.