4.6 Pedestrian Signal Displays, Countdown Modules, Interval Timing & APS

4.6 Pedestrian Signal Displays, Countdown Modules, Interval Timing & APS

Pedestrian Signal Displays & Countdown Modules

Pedestrian signal heads are governed by MUTCD 11th Edition Chapter 4I — Section 4I.01 (pedestrian signal heads), 4I.02 (size, design, illumination), 4I.03 (location and height), 4I.04 (countdown signals), 4I.05 (pedestrian detectors), and 4I.06 (pedestrian intervals and signal phases). Chapter 4E covers vehicular indications only, so any reference to "4E.06" or "4E.11" for pedestrian material is a 2009-edition number that no longer exists. Pedestrian displays communicate right-of-way through two standardized symbols:

• Walking Person Symbol (WALK): Displayed in illuminated lunar white. Communicates that pedestrians facing the signal may leave the curb and begin crossing.
• Upraised Hand Symbol (DON'T WALK): Displayed in illuminated Portland orange. Communicates whether crossing is prohibited or clearance is active.

The Countdown Pedestrian Signal Standard (Section 4I.04)

Paragraph 1 is a Standard: all pedestrian signal heads used at crosswalks where the pedestrian change interval is more than 7 seconds shall include a pedestrian change interval countdown display. This applies to existing heads, not only new installations. Paragraph 2 is an Option: where the pedestrian change interval is 7 seconds or less, a countdown display may be provided.

1. Display Construction (Paragraph 4): countdown signals shall consist of Portland orange numbers at least 6 inches in height on a black opaque background, located immediately adjacent to the associated UPRAISED HAND indication. Guidance in Paragraph 8 raises that to at least 9 inches only where pedestrians enter the crosswalk more than 100 feet from the display. Quoting 9 inches as the general minimum is a common error.
2. Counting Window (Paragraphs 3, 5, and 6): the countdown shall always be displayed simultaneously with the flashing UPRAISED HAND for that crosswalk. The count shall begin only at the beginning of the pedestrian change interval, and after it displays zero the display shall remain dark until the next countdown. Countdown displays shall not be used during the walk interval, and shall not be used during the red clearance interval of a concurrent vehicular phase that ends simultaneously with or after the pedestrian phase.
3. Preemption (Paragraph 10, Guidance): if the pedestrian change interval is interrupted or shortened as part of a transition into a preemption sequence (Section 4F.19), the countdown display should be discontinued and go dark immediately on activation of the preemption transition.
4. Non-concurrent phases (Paragraph 7, Guidance): where a pedestrian head has no concurrent vehicular phase, the flashing UPRAISED HAND should be set approximately 4 seconds less than the required pedestrian clearance time, with an additional steady UPRAISED HAND clearance interval before the conflicting vehicular phase begins.
5. Separate timing devices (Paragraph 9): some countdown products time independently of the controller, so the engineer must re-verify the display whenever pedestrian change interval timing is edited.

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Pedestrian Clearance Intervals and Timing Calculations

Pedestrian clearance timing is governed by human walking biomechanics and roadway cross-section geometry:

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|                     MUTCD Pedestrian Timing Formulation                        |
+--------------------------------------------------------------------------------+
|                                                                                |
|   1. Pedestrian Change Interval (Flashing Don't Walk - FDW):                   |
|                                                                                |
|                   D                                                            |
|         FDW  =  -----                                                          |
|                  S_p                                                           |
|                                                                                |
|      Where:                                                                    |
|      - D   = Crossing distance from curb to far edge of traveled way (ft)      |
|      - S_p = Pedestrian walking speed (standard: 3.5 ft/sec; reduced: 3.0)     |
|                                                                                |
|   2. Minimum Total Pedestrian Time Check (Walk + FDW):                         |
|                                                                                |
|                              D_total                                           |
|         Walk  +  FDW   >=   ---------                                          |
|                                S_p                                             |
|                                                                                |
|      Where:                                                                    |
|      - D_total = Distance from the pedestrian detector, or from a point       |
|                  6 ft behind the curb face if no detector, to the far side    |
|      - S_p     = 3.0 ft/sec for this walk-plus-clearance check (4I.06 P14)    |
+--------------------------------------------------------------------------------+

Step-by-Step Practical Calculation

A senior technician calculates pedestrian clearance for an arterial crossing:

• Curb-to-curb crossing distance to the far side of the traveled way ($D$) = 56 feet.
• No pedestrian detector present, so the walk-plus-clearance check starts 6 feet behind the curb face per Section 4I.06, Paragraph 14: $D_{total} = 56 + 6 = 62\text{ feet}$.
• Pedestrian clearance walking speed ($S_p$) = 3.5 ft/sec (Paragraph 7).
• Walk-plus-clearance check speed ($S_p$) = 3.0 ft/sec (Paragraph 14).

1. Calculate the required pedestrian clearance time: $t_{\text{clear}} = \frac{56\text{ ft}}{3.5\text{ ft/sec}} = 16.0\text{ seconds}$
2. Allocate it between FDW and buffer (Paragraph 4): the sum of the pedestrian change interval (FDW) and the buffer interval shall not be less than the calculated pedestrian clearance time, and the buffer must be at least 2 seconds. Setting $FDW = 16.0\text{ s}$ with a 2.0 s buffer gives 18.0 s, comfortably satisfying the requirement. (Timing FDW at 14.0 s with a 2.0 s buffer would also satisfy it; timing FDW at 16.0 s is the conservative and more common agency practice.)
3. Check the walk-plus-clearance total at 3.0 ft/sec: $\text{Total Required} = \frac{62\text{ ft}}{3.0\text{ ft/sec}} = 20.7\text{ seconds}$ $\text{Minimum Walk} = 20.7\text{ s} - 16.0\text{ s} = 4.7\text{ seconds}$
4. Apply the walk interval Guidance (Paragraphs 11 and 12): the walk interval should be at least 7.0 seconds so pedestrians have adequate opportunity to leave the curb; walk intervals as short as 4 seconds may be used if pedestrian volumes and characteristics do not require 7. Here the 7-second Guidance governs because it exceeds the 4.7 s computed minimum:
   • Walk Interval = 7.0 seconds
   • FDW Interval = 16.0 seconds
   • Buffer Interval (steady UPRAISED HAND) = 2.0 seconds minimum
   • Total Pedestrian Service Time = $7.0 + 16.0 = 23.0\text{ seconds}$, which exceeds the 20.7 s walk-plus-clearance requirement.
5. Pedestrian Buffer Interval (Paragraph 4, Standard): a steady UPRAISED HAND must be displayed for at least 2 seconds after the pedestrian change interval and before any conflicting vehicular movement is released. The buffer shall not begin later than the beginning of the red clearance interval, if one is used. Many agencies set the buffer equal to the vehicular yellow plus red clearance, which exceeds the 2-second minimum, but 2 seconds is the MUTCD floor.
6. Extended push button press (Paragraph 8, Option): a walking speed of up to 4 ft/s may be used to evaluate pedestrian clearance sufficiency where an extended push button press provides slower pedestrians a longer clearance on request, and passive detection may adjust clearance automatically.

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Accessible Pedestrian Signals (APS) & PROWAG Standards

Accessible Pedestrian Signals (APS) communicate pedestrian crossing indications in non-visual formats — audible tones, speech messages, and vibrating tactile arrows — for blind or low-vision pedestrians. In the 11th Edition they have their own chapter: Chapter 4K, comprising 4K.01 (general), 4K.02 (location), 4K.03 (walk indications), 4K.04 (vibrotactile arrows and locator tones), and 4K.05 (extended push button press features), read alongside the U.S. Access Board's PROWAG:

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|                 Accessible Pedestrian Signal (APS) Specifications              |
+--------------------------------------------------------------------------------+
| 1. Vibrotactile Arrow: Raised arrow on pushbutton vibrates during WALK.       |
| 2. Locator Tone: <= 0.15 s duration, repeating at 1-second intervals whenever |
|    the audible walk indication is NOT active (4K.04 P4).                      |
| 3. Audible Walk Indication: 8-10 ticks/s, multiple frequencies with a         |
|    dominant component at 880 Hz, or a speech walk message (4K.03 P7-P8).      |
| 4. Volume: set to a MAXIMUM of 5 dBA louder than ambient (Guidance);          |
|    automatic adjustment up to a maximum of 100 dBA (Standard, 4K.03 P10).     |
+--------------------------------------------------------------------------------+

1. Vibrotactile Pushbuttons

• The APS pushbutton features a raised, high-contrast tactile arrow pointing in the exact direction of travel across the crosswalk.
• During the WALK interval, an internal motor drives a vibrotactile oscillation, vibrating the arrow so a blind pedestrian resting their hand on the button feels the onset of WALK without relying on hearing.

2. Pushbutton Locator Tone

• Section 4K.04, Paragraph 4 (Standard): push button locator tones shall have a duration of 0.15 seconds or less and shall repeat at 1-second intervals at all times that the audible walk indication is not active — including during the pedestrian change interval and while the pedestrian signal is resting in walk.
• Paragraph 8 (Guidance): the locator tone should be audible 6 to 12 feet from the push button, or to the building line, whichever is less.
• Paragraph 6 (Standard): locator tones shall be deactivated when the signal or pedestrian hybrid beacon is operating in flashing mode, except where pedestrian actuation brings the device from flashing or dark into steady operation.
• Paragraph 7 (Standard): locator tones shall be intensity responsive to ambient sound.
• Paragraph 5 (Option): the locator tone may default off during the steady UPRAISED HAND if passive pedestrian detection reactivates it whenever a pedestrian is present within a 12-foot radius of the push button.

3. Audible Walk Indications (Percussive Tick vs. Speech)

• Percussive Tone (Section 4K.03, Paragraphs 7 and 8): at midblock crossings, on corners carrying only one APS, in a median, and on corners where two APS are separated by a distance of at least 10 feet, the audible walk indication shall be a percussive tone. Audible tone walk indications shall repeat at eight to ten ticks per second and shall consist of multiple frequencies with a dominant component at 880 Hz.
• Speech Walk Messages: where two APS on the same corner serving different crosswalks are placed less than 10 feet apart or on the same pole, the audible walk indication shall be a speech walk message (Section 4K.02, Paragraph 3, and 4K.03, Paragraph 7), because a percussive tone would be directionally ambiguous. Paragraph 17 requires a speech walk message to give a clear message naming the street being crossed; the MUTCD does not prescribe a repetition count.

4. Automatic Ambient Noise Volume Adjustment

• APS units incorporate an integrated microphone that continuously monitors ambient traffic noise.
• Section 4K.03, Paragraph 9 (Guidance): the volume of audible walk indications and push button locator tones should be set to be a maximum of 5 dBA louder than ambient sound, except where audible beaconing is provided in response to an extended push button press. The 11th Edition states a ceiling only — there is no "2 dB minimum above ambient" in the current MUTCD, although older material commonly quotes a 2-to-5 dB range.
• Paragraph 10 (Standard): automatic volume adjustment up to a maximum volume of 100 dBA in response to ambient traffic sound level shall be provided.
• Paragraph 11 (Guidance): sound levels should be adjusted low enough to avoid misleading blind pedestrians where an island allows unsignalized right turns across a crosswalk, where multi-leg or complex phasing creates more than two pedestrian phases, or where diagonal crossings or simultaneous WALK indications on different streets could confuse which crosswalk a tone serves.