Accessible Pedestrian Signals: 

Installation Details 

Janet M. Barlow, COMS, Accessible Design 

for the Blind 

“Access to civic life by people with disabilities is a 

fundamental goal of the Americans with 

Disabilities Act (ADA). To ensure that this goal is

met, Title II of the ADA requires State and local 

governments to make their programs and 

services accessible to persons with disabilities. 

This requirement extends not only to physical 

access at government facilities, programs, and 

events -- but also to policy changes that 

governmental entities must make to ensure that 

all people with disabilities can take part in, and 

benefit from, the programs and services of State 

and local governments. In addition, governmental 

entities must ensure effective communication -- including the provision of necessary auxiliary 

aids and services -- so that individuals with disabilities can participate in civic life.” 

–US Department of Justice: The ADA and City Governments: Common Problems 

Introduction 

Today’s wide and increasingly congested intersections and complex 

signalization schemes often fail to provide adequate non-visual information 

for crossing analysis and decisions by pedestrians who are blind or who 

have low vision. For the effective communication required by the 

Americans with Disabilities Act (ADA) of 1990, the WALK/DON’T WALK 

indications of visual pedestrian signal heads must be conveyed to 

pedestrians who don’t use visual cues. Accessible Pedestrian Signals 

(APS) provide this information through audible and vibrotactile indications. 

The availability of improved technologies and the adoption of technical 

standards in the Manual on Uniform Traffic Control Devices (MUTCD) 1

have led to significant increases in the number of APS installations over 

the past few years. 

Draft revisions to the MUTCD2

, harmonized with the US Access Board’s 

draft Public Rights-of-Way Accessibility Guidelines (draft PROWAG)3

, 

specify pushbutton-integrated APS with speakers and vibrating 

surfaces incorporated in the pedestrian pushbutton housing. These 

provide crossing indications to the waiting pedestrian at the departure 

curb rather than from overhead, as in older technology, and permit 

speaker volume to be set at a significantly lower and less obtrusive 

level. New tones -- ticks, clicks and other electronic sounds -- and 

 

1

 MUTCD, 2003 http://mutcd.fhwa.dot.gov/htm/2003r1r2/part4/part4e.htm

2

 MUTCD, Notice of Proposed Amendments, 1/2/08. http://mutcd.fhwa.dot.gov/resources/proposed_amend/index.htm

3U.S. Access Board, Draft Public Rights-of-Way Accessibility Guidelines, 2005, http://www.access-board.gov/prowac/

Figure 1 Pushbuttonintegrated APS 

(Polara)
Accessible Pedestrian Signals: Installation Details 2 

speech messages replace the often-irritating ‘cuckoos’ and ‘chirps’ of yesterday. Tactile 

arrows and other features -- pushbutton locator tones, additional audible or Braille 

information, crosswalk maps, actuation indicators -- enhance the effectiveness of these new 

devices. 

As with vehicular signals, APS must be installed, wired, coordinated, oriented, and adjusted 

so the information they provide about a street crossing is effectively communicated and 

reliable, so it will be safe in use. This requires the same careful attention to location and 

direction that is needed in the installation of traffic signals, with a particular focus on the 

sound and tactile features of the device in addition to visual features and timing attributes. 

Researchers and orientation and mobility specialists who specialize in travel and street 

crossing skills4

 report that some APS installations do not provide the necessary usability. In 

the case studies that follow, some common problems are identified, and remedies 

recommended. 

But first, a brief description of APS features and installation requirements: 

Pushbutton-integrated APS 

Figures 1 and 2 show several of the pushbutton-integrated APS devices that are available in 

the US. All include a pushbutton that is at least 50 mm (2 inches) in diameter, audible and 

vibrotactile WALK indications, a pushbutton locator tone, a tactile arrow, and automatic 

volume adjustment. Configuration, functioning, and adjustment methods vary somewhat by 

manufacturer.5

 

Figure 2 Examples of pushbutton-integrated APS from various manufacturers 

(left to right: Campbell, Prisma, Novax, Panich; Polara shown in figure 1) 

Location 

Pushbutton-integrated APS rely on relative proximity to the crossing location, not on 

difference in sounds, to clarify which street crossing is being signaled. MUTCD revisions and 

draft PROWAG, supported by recent research, specify that each APS device shall be 

installed on a separate pole. Devices must be located a minimum of 3m (10 feet) apart, no 

 

4

 To locate an orientation and mobility specialist, see http://aerbvi.org/modules.php?name=Content&pa=showpage&pid=4

for a list of chapters of the Association for the Education and Rehabilitation of the Blind and Visually-Impaired (AER). 

5

 See ‘Interfacing Accessible Pedestrian Signals with Traffic Signal Control Equipment’ at http://www.accessboard.gov/research/APS/report.htm
Accessible Pedestrian Signals: Installation Details 3 

more than 3m (10 feet) 

maximum from the curb 

line (and closer, if 

possible), and between 

the curb ramp landing 

and the outside 

crosswalk line, or no 

more than 1.5m (5 feet) 

maximum from the 

outside crosswalk line.6 7

 

See Figures 38

 and 4 for 

illustrations of 

pushbutton locations. 

Devices that are located 

on existing mountings 

may not be able to 

provide optimal usability, 

particularly for the 

vibrotactile feature. APS 

should be located so 

pedestrians using the 

audible or vibrotactile 

indications can align and 

prepare for the crossing 

while standing close to 

the device AND the 

crossing departure point. 

For graphics showing APS at corners with 10 foot and 30 foot radii and various types of curb 

ramps, see the curb ramp library, chapter 6, in Special Report: Accessible Public Rights-ofWay – Planning and Designing for Alterations9

 and examples in Figure 4E-3 of draft 

MUTCD10

. 

 

6

http://www.access-board.gov/prowac/draft.htm#306

7

http://mutcd.fhwa.dot.gov/resources/proposed_amend/index.htm

8

 Figure from CHRP Web Only Document 117-A, Accessible Pedestrian Signals: A Guide to Best Practice, Figure 6-8 

9

 PROWAAC Special Report: Accessible Public Rights-of-Way, Planning and designing for Alterations, Institute of 

Transportation Engineers 2007. http://www.access-board.gov/prowac/alterations/guide.htm#intro6

10 MUTCD Proposed figures. http://mutcd.fhwa.dot.gov/resources/proposed_amend/npa_figures.pdf

Figure 3 Optimal location of pushbutton-integrated APS – two 

pushbuttons on one corner, mounted on two separated poles – rapid tick 

WALK indication 
Accessible Pedestrian Signals: Installation Details 4 

Figure 4 Installation of APS on two separated poles, aligned with crosswalk lines (APS devices circled in 

red) 

Pushbutton locator tone 

The pushbutton locator tone is a low-volume tick or tone that repeats constantly, at onesecond intervals, during the flashing and steady DON’T WALK intervals to advise pedestrians 

of pushbutton availability and location. Its volume must be carefully adjusted to be audible a 

minimum of 1.8 m (6 feet) and a maximum of 3.7 m (12 feet) from the pushbutton, or to the 

building line, whichever is less. The pushbutton locator tone on a properly-installed 

pushbutton can also indicate the crossing location to an approaching pedestrian and may 

provide useful cues to an irregular crossing. 

Audible WALK indications 

Audible WALK indications are broadcast from a speaker that is incorporated into the 

pedestrian pushbutton housing. When the pedestrian pushbutton is properly located close to 

the departure curb, a low-volume WALK signal will be adequate for usability. Although most 

devices can also provide on-demand audible beaconing, the standard audible indication is 

not intended to be heard across the street. As with pushbutton locator tones, the volume of 

the audible WALK indication must be carefully adjusted to be heard a minimum of 1.8 m (6 

feet) and a maximum of 3.7 m (12 feet) from the pushbutton, or to the building line, whichever 

is less. 

Device technology automatically samples audible output and compares it to ambient sound, 

adjusting volume accordingly. Note that louder is not better -- an installation that is too loud 

may mask critical vehicle sounds and be difficult to localize and use for guidance. 
Accessible Pedestrian Signals: Installation Details 5 

Rapid tick WALK indication. Where pushbutton APS are located on separate poles, as 

required in new construction (and where feasible in alterations), the recommended audible 

WALK indication is a fast ticking or beeping percussive sound at 8-10 repetitions per second. 

Research11 shows that using the same sound for both crossings results in more accurate and 

faster responses than two different sounds or speech messages if APS are separated and 

each is located close to the crossing it signals. 

Speech WALK indication. When two APS are mounted on the same pole, or are located 

closer than 10 feet to each other, using different tone indications (such as the cuckoo/chirp of 

older technology) provides ambiguous information that could result in a pedestrian crossing 

on the wrong signal.12 13 14 15. When two APS must be located closer than 10 feet apart in an 

alteration where it is infeasible to separate them, speech WALK indications and other 

features are required to distinguish the crossings.

If speech messages are used, the recommended WALK message is “[street name], WALK 

sign is on to cross [street name]. 16 For example, “Peachtree, WALK sign is on to cross

Peachtree, Peachtree, WALK sign is on to cross Peachtree”. This message is repeated for 

the duration of the WALK indication. Speech WALK indications must be accompanied by 

tactile arrows and Braille labels so that pedestrians who are blind can determine street 

names17

. 

Vibrotactile WALK indications 

Vibrotactile indications are transmitted by a vibrating plate or arrow on the housing of the 

pedestrian pushbutton. During WALK, the arrow or plate vibrates. Thus, a pedestrian must 

be able to stand with a hand on the device while he/she is aligned and waiting to begin 

crossing. The vibrotactile indication is particularly useful for pedestrians who have both 

hearing and visual impairments and also allows pedestrians to tactually confirm audible 

signal information in noisy environments. 

Tactile arrow 

The tactile arrow on the device must be aligned with the direction of travel on the crosswalk 

and point toward the street crossing that the pushbutton controls and signals. For most 

devices, this requires aligning the face of the device and pushbutton with the crosswalk lines. 

This takes care in installation, particularly when drilling mounting holes for the device. 

 

11 Scott, A.C., Myers, L., Barlow, J.M., and Bentzen, B.L. Accessible pedestrian signals: The effect of pushbutton location 

and audible WALK indications on pedestrian behavior. Transportation Research Record: Journal of the Transportation 

Research Board. 2005. Number 1939, pp 69-76. 

12 Ashmead, D.H., Wall, R.S., Bentzen, B.L. and Barlow, J.M. Which Crosswalk? Effects of accessible pedestrian signal 

characteristics. ITE Journal. 2004. 74-9, pps 26-31. 

13 Bentzen, B.L., Barlow, J.M., and Franck, L. Addressing barriers to blind pedestrians at signalized intersections. ITE 

Journal. 2000. 70-9, pps. 32-35. 

14 Carroll, J. and Bentzen, B.L. American Council of the Blind survey of intersection accessibility. The Braille Forum,

1999. 38(7), pps. 11-15. 

15 Uslan, M.M., Peck, A.F., and Waddell, W. Audible traffic signals: how useful are they? ITE Journal, 1988. 58, pps. 37-

43. 

16 Bentzen, B.L., Barlow, J.M., Franck, L. Speech messages for accessible pedestrian signals. ITE Journal. 2004. 74-9, pps 

20-24. 

17 MUTCD NPA contains specifications of features required with speech messages in 4E.09. 

http://mutcd.fhwa.dot.gov/resources/proposed_amend/npa_text.pdf
Accessible Pedestrian Signals: Installation Details 6 

Other Features 

Most pushbutton-integrated APS can provide additional features. These may include Braille 

labels for street names, actuation indicators (a light or beep), tactile crosswalk maps, and 

options activated by an extended button push: audible beaconing (useful for directional 

guidance at irregular or long crossings), extended pedestrian timing, and recorded 

information of street names or additional information about the intersection. 

For further information, see NCHRP Web-only Document 117A, Accessible Pedestrian 

Signals: A Guide to Best Practice18, available online. 

Installation case studies 

Issue 1. APS volume (louder is not better) 

Issue 2. Location, location, location 

Issue 3. Which signal? Speech indications required

Issue 4. Wrong pole 8Wrong message 

Issue 5. Tactile arrow (In-line) 

Issue 6. Pre-timed installations (an APS is more than a pushbutton) 

Issue 7. Repair/replacement (put it back right!) 

Issue 8. Rest-in-WALK installations (quiet time OK)

Issue 9. Reach (how far?) 

Issue 10. Braille (right side up!) 

Issue 11. Good vibrations (vibrotactile indications) 

Issue 12. Audible beaconing 

Issue 13. Stub poles 

Issue 14. Inspection (beware of field changes) 

Issue 15. Installation errors increase risk 

 

18 Barlow, J.M., B. L. Bentzen, D. Harkey, D. Carter. Accessible Pedestrians Signals: A Guide to Best Practice. NCHRP 

Web only document 117A. National Cooperative Highway Research Program, Washington, D.C. 2007. 

http://onlinepubs.trb.org/onlinepubs/nchrp/nchrp_w117a.pdf and at www.walkinginfo.org/aps. 
Accessible Pedestrian Signals: Installation Details 7 

Issue 1: APS volume 

Louder is NOT better. It is common to find APS volumes set so loud that the pushbutton 

locator tone and audible walk indication can be heard at midblock or across the street -- or in 

a quiet office or bedroom nearby. This can lead to neighborhood as well as user concerns, 

since excessive volume will mask other sounds that are important to pedestrians who are 

blind (such as the sound of traffic surges or the indication of another APS on the same 

corner). 

An APS signal should be audible at the beginning of the crosswalk, but no more than 3.7 m 

(12 ft) from the pushbutton, or to the building line, whichever is closer. Technologies that 

broadcast from above required higher- volume settings to be effective, and often were 

labeled neighborhood nuisances. Modern pushbutton-integrated devices provide the signal 

right where it is needed -– at the departure curb –- so it needs to provide only a 2-5 dB gain 

over ambient noise to signal the pedestrian interval. Click or tick tones are less apt to annoy 

and are more detectable in traffic noise than the older cuckoo/chirp outputs19. They are also 

less likely to be confused with a bird. 20 21

Remedy: When APS noise annoys, reduce the signal volume. Volume adjustments differ by 

manufacturer: some devices can be set through a hand-held PDA, while others require 

adjusting set screws on a control board mounted in the pedestrian signal head. APS volume 

should be set individually at every location. Note that nearby building facades or other hard 

surfaces that reflect the APS signal may actually cause the APS to increase in volume in 

reaction to its own sound, if the sound or ambient sound response is set too loud. Sound 

baffles may also be necessary in some locations. It’s important to adjust the APS and listen 

carefully. For particularly difficult situations with very near neighbors or nearby hard reflective 

surfaces, consider a change in sound type from a beep to a tick or click, which may be less 

annoying to listeners.

In most devices, the pushbutton locator tone volume and the WALK indication volume are set 

separately, and each has a minimum/maximum range. If there is a lot of traffic noise at some 

times of the day, the maximum volume of both the pushbutton locator tone and the WALK 

indication may need to be relatively loud, near 90 dB. However, the minimum volumes could 

be set in the 30 – 40 dB range to avoid annoyance at night, or when traffic volumes and 

ambient sound levels are low. 

The response-to-ambient sound operates in conjunction with the volume settings, but is 

usually set separately. If the ambient sound adjustment is set to respond at 15 dB over 

ambient, APS are likely to be too loud when there is noise at the intersection, even if volume 

is appropriate for times when the intersection is quiet. The MUTCD specifies a sound volume 

at least 2, but no more than 5, dB over ambient. 

The installer or an assistant should walk approximately 10 feet away from the device and 

listen to its volume during fluctuations in traffic before finalizing the volume adjustments. The 

installer should also listen from a distance of approximately 30 feet away. If adjusting an 

APS that requires opening the pedestrian signal head to get to the control board and make 

the sound adjustments, the pedhead should be closed, and all reflective materials, such as 

ladders, should be moved away before this ‘final listen’.

 

19 Wall, R.S., D.H. Ashmead, B.L. Bentzen, & J. Barlow. Directional guidance from audible pedestrian signals for street 

crossing. Ergonomics. 2004. Vol. 47, (12), 1318 – 1338. 

20 Carroll & Bentzen. p. 14. 

21 Bentzen, Barlow & Franck, 2000, p 34. 
Accessible Pedestrian Signals: Installation Details 8 

Issue 2: Location relative to the crosswalk 

An APS that is mounted outside the crosswalk area may provide misleading information 

about the crossing location. Pedestrians who are blind may stand beside the pushbutton 

while waiting to cross, particularly if they use the vibrotactile indication. 

In the situation pictured in 

Figure 5, pedestrians who 

begin their crossing beside the 

pushbutton would be outside 

the crosswalk lines and may 

not be anticipated by turning 

drivers. If the pedestrian who 

is blind also encounters the 

median island and stops, 

there is no APS or pushbutton 

on the median to call a WALK 

to complete the second half of 

the crossing. Since the APS is 

not close to the crosswalk and 

curb ramp, the volume of the 

audible walk indication and 

pushbutton locator tone must 

also be louder in order to be 

heard from the crossing 

location. 

Remedy: One solution is to move the pole closer to the crosswalk lines, so the device is in 

reach of the landing of the curb ramp and adjacent to the crosswalk. This will assist 

pedestrians who are blind in finding the APS pushbutton and in beginning crossing from 

within the crosswalk area.

In existing streetscapes, without a median, it may also be possible to widen the crosswalk 

(and adjust the stop line accordingly) to eliminate the offset. 

Vehicular signal poles are rarely in optimal position for mounting APS pushbuttons. A better 

choice is to provide an individual stub pole or pedestrian signal pole at the top of every curb 

ramp. Where the sidewalk is separated from the curb, use a returned curb rather than a flare 

at the ramp (good for wayfinding, if properly aligned) and locate the stub pole within the 

border adjacent to the landing at the top of the ramp. For recommended pedestrian 

pushbutton locations at a variety of ramp types, see Chapter 6 in the PROWAAC Special 

Report.22

. 

 

22 PROWAAC Special Report: Accessible Public Rights-of-Way, Planning and designing for alterations. (2007) Institute of 

Transportation Engineers. 

Figure 5 APS is located about 8 feet from the crosswalk and curb 

ramp landing
Accessible Pedestrian Signals: Installation Details 9 

Issue 3: Which signal? Speech WALK messages required 

In numerous installations evaluated in the 

field, where two APS were mounted on 

the same pole, installers failed to 

customize the messages and used the 

manufacturer’s default message, ‘WALK 

sign is on’. With two APS located closer 

than five feet to each other, it is 

impossible to distinguish which one is 

sounding based on the location and 

direction of the sound. Pedestrians 

standing at one crosswalk could mistake 

the message of the other crosswalk for 

their indication to begin crossing. 

Remedy: If possible, move the APS to 

separated poles, each close to the 

crosswalk it controls and indicates (see 

Figures 3 & 4). 

In Figure 6, it appears that the required separation of APS mounting poles (10 feet minimum) 

could have been achieved here by locating stub poles to the left side of the left ramp and the 

right side of the top crossing. That would have provided much less ambiguous information for 

pedestrians using these crossings. While a common pole is permitted where existing 

constraints preclude separated poles, it should not be the selected solution where separated 

poles are possible. 

But where constraints in an existing developed streetscape prohibit separating pedestrian 

pushbuttons (as is required in new construction), pushbuttons can be mounted on a single 

pole. However, the speech messages must be different (in order for the pedestrian to 

distinguish which one is sounding) and the message must include the street name. 

This will require ordering and installing -- in the proper device! -- custom speech chips for 

both the WALK message and the pushbutton information message to identify, by name, the 

street that the device controls. Some manufacturers provide equipment so jurisdictions can 

record their own messages. If used, care must be taken in recording messages with proper 

wording and clear speech. 

Speech messages should include the street name and use this tested format: ‘Howard. 

WALK sign is on to cross Howard’. A pushbutton information message (activated by an 

extended button push) must say: ‘WAIT to cross Howard at Grand. WAIT.’ (See Figure 6). In 

addition, the APS should include Braille street name identification and a tactile arrow, 

carefully aimed to be in line with the crosswalk lines. 

Figure 6 Example of pushbutton information messages

and speech walk messages, if two APS must be 

mounted on the same pole Alterations only
Accessible Pedestrian Signals: Installation Details 10 

Issue 4: Wrong pole! 8Wrong message! 

In Figure 7, APS have been installed on the wrong poles. The APS on the pole in the left of 

the photo has an arrow pointing toward the street on the right in the photo. Since the APS is 

closer to the departure curb and curb ramp for crossing straight ahead (in line with the 

photographer’s direction of travel), a pedestrian hearing the sound from that APS would 

expect that the APS governs that crossing, and may not even be able to hear the further 

distant APS that is actually for the crossing he/she intends (in the foreground of Figure 7). 

Remedy: Each APS should have been installed on the pole closest to the crosswalk it 

controls, as shown in Figure 8. For example, the APS for the crossing on the right in Figure 7 

should be installed on the pole near the right side of the photo, and on the side of the pole 

toward the curb ramp, but still reachable from the level sidewalk. This will allow pedestrians 

to push the button and then hear the APS at the crosswalk departure point. The APS on the 

pole to the left in Figure 7 should be parallel to the crosswalk that it should control (the one 

straight ahead in the photographer’s view). 

It may be possible to realign the APS on each pole and reconnect the wiring. However, APS 

can be wired to a control board in the pedestrian signal head or through the controller, so it 

may be necessary to move the pedestrian signal head (or to completely rewire each APS) to 

conform. The wiring and device output needs to be checked after modification to assure that 

the APS is signaling the correct crossing phase. 

If the APS has a speech message, the APS needs to be moved to the pole closer to the 

crosswalk it signals, which will also require reversing the arrow and signs on the APS 

housing. If speech WALK messages or pushbutton information messages are installed, the 

functioning and accuracy of both should be checked after re-installation of APS devices. 

Installation of the APS on a stub pole or separate pedestrian signal pole, as shown in Figure 

8, rather than on a mast arm pole, is likely to provide better placement. 

Figure 8 Installation where APS are installed in 

wrong locations; both are too far from street 

they control and will be heard as closer to the 

other street

Figure 8 Installation where APS are installed in 

correct locations in relation to crosswalks
Accessible Pedestrian Signals: Installation Details 11 

Issue 5: Tactile arrow (in line) 

Misleading wayfinding information will be conveyed if the tactile arrow is oriented toward the 

center of the intersection, rather than parallel to the crosswalk. In the photo below (Figure 9), 

the arrow is out of alignment with the crosswalk direction. Even small misalignments can 

inadvertently direct a blind pedestrian outside the crosswalk area or into the parallel traffic. 

Remedy: The APS needs to be removed and reinstalled. The arrow must be aligned with 

the direction of travel on the 

crosswalk. 

Since the tactile arrow is on the face 

of the device or on the pushbutton, 

the APS mounting affects arrow 

alignment. If the needed adjustment 

is minor, it may be possible to shim 

behind one side of the device to align 

the arrow with the crosswalk. In other 

cases, it may be necessary to drill 

new mounting holes and reposition 

the APS on the pole. The arrow 

should be aligned as shown in Figure 

10. 

Figure 9 Tactile arrow not aligned with crosswalk direction 

Figure 10 Location where tactile arrow is aligned with 

direction of travel on the crosswalk
Accessible Pedestrian Signals: Installation Details 12 

Issue 6: Pre-timed signals (an APS is more than a pushbutton) 

Since pedestrians don’t need to use the pushbutton to get a WALK signal at pre-timed 

signals or where pedestrian signals are on recall, some transportation professionals have 

concerns and questions about installation of pushbutton-integrated APS at those locations. 

The pushbutton locator tone in a pushbutton-integrated APS provides access to other 

information provided by the APS unit: the vibrotactile WALK; the tactile arrow for wayfinding; 

tactile mapping; if provided, and messages and actions available with an extended button 

push, such as audible beaconing or an extended crossing time. Thus pushbutton-integrated 

APS should be installed at pre-timed locations even if it is not necessary to use the 

pushbutton to call the WALK. 

Some pedestrians may push the pushbutton when it is unnecessary, but that is not really a 

problem if the pushbutton is beside the crossing departure location. Regular intersection 

users will come to understand that they don’t have to push the pushbutton. If the actuation 

light is lit when the call is made, pedestrians who can see the actuation indicator will be able 

to recognize that the pedestrian call has already been made. 

Remedy: Pushbutton-integrated APS are typically wired to the pedestrian signal and function 

as the pedestrian signal functions. APS, in typical operation, provide relatively quiet sounds 

from a location beside the crosswalk. Previous concerns about APS at pre-timed locations in 

downtown areas mainly stemmed from too-loud signals mounted on pedestrian signal heads, 

which echoed off buildings. 
Accessible Pedestrian Signals: Installation Details 13 

Issue 7: Repair/replacement (put it back right!) 

An APS that was knocked down in a crash was reinstalled by workers who did not know how 

the device was supposed to function. After reinstallation, the APS was turned 90 degrees 

from its prior placement, and the tactile arrow was no longer pointing at the street the 

pushbutton controlled. The WALK message was provided at the wrong time for the street 

toward which the arrow pointed. 

In another situation, shown in Figure 11, the APS was temporarily reinstalled, still functioning, 

but oriented incorrectly. It was several weeks before a crew reinstalled it properly. 

Meanwhile it provided inaccurate information. When the APS is not correctly installed, there 

is a risk that a person who is blind will cross a street with the wrong WALK indication or in the 

wrong direction. 

Remedy: All maintenance 

personnel need to know enough 

about APS installations to 

recognize an APS, and to either 

call someone to check details of 

reinstallation, or to correctly reinstall the APS themselves. 

Training is needed to avoid 

dangerous errors in reinstallation 

or repair. 

Figure 11 APS that was damaged in a crash and temporarily 

reinstalled with wire
Accessible Pedestrian Signals: Installation Details 14 

Issue 8: Rest-in-WALK (quiet time ok) 

In some locations, the pedestrian signals ‘rest-in-WALK’ and it may not be desirable to have 

the WALK indication repeat constantly during the long walk interval, because the WALK 

indication is a more constant sound than the locator tone. 

Remedy: Draft PROWAG and proposed MUTCD language provides specific exceptions for 

‘rest-in-walk’ situations.23 24 The audible WALK indication can be set to sound during the first 

seven seconds of the walk interval only and then revert to the locator tone. If someone 

presses the pushbutton during the walk interval, the WALK message can be set to sound 

again for seven seconds, or as long as the remaining time in the WALK, whichever is less. 

The vibrotactile indication usually vibrates during the entire walk interval. 

When ordering APS for use in rest-in-WALK locations, or where pedestrian signal is on recall 

with long walk intervals, designers should check that the manufacturer offers options for restin-WALK settings. 

 

23 MUTCD NPA, 4E.06 

24 Draft PROWAG, R306.2 
Accessible Pedestrian Signals: Installation Details 15 

Issue 9: Reach (how far? 

APS devices can be located in landscaped areas if the 

pushbutton is reachable from a level paved area. Figure 

12 shows a location where new APS (and new 

sidewalks) were installed, but the APS are not usable. 

Besides the inaccessibility for wheelchair users, a

person who is blind will have difficulty finding and getting 

to the pushbutton, even with the pushbutton locator tone 

sounding. 

Remedy: Installation in landscaped areas must be 

carefully planned and monitored for accessibility. APS 

must be within the reach range (1.2 m/48 inches 

vertically, .25m/10 inches horizontally) for an individual 

who uses a wheelchair.25

 

The APS shown in Figure 13 are 

appropriately located within the 

landscape strip, reachable from a 

paved level surface, and aligned with 

the crosswalk lines. 

Figure 13: APS installed on poles in the 

landscape strip, and still within reach from 

a level paved sidewalk surface 

 

25 Draft PROWAG, R404. 

Figure 12 In this new construction, 

APS is located too far from the 

sidewalk to be reached by a user of a 

wheelchair or scooter
Accessible Pedestrian Signals: Installation Details 16 

Issue 10: Braille (right side up?) 

Where the APS device includes the 

street name in Braille, care must be 

taken to install the signs in the correct 

location and orientation. 

Manufacturers usually impress the 

Braille into a standard metal sign 

attached to the APS housing. The 

typical sign includes print arrows and 

pedestrian symbols, often on both 

sides of the sign so that it can be 

flipped over to be installed on either 

side of the street. However, when 

Braille is added, the sign can no longer 

be reversed. Flipping the sign results 

in indented and backwards Braille 

symbols, which are unreadable. 

Remedy: Braille is made up of small 

dots in a grid which are raised on the 

surface to be read by fingertip. 

Contractors and installers need to 

know that the Braille dots should be raised and should check all labels and instructions 

carefully. 

Manufacturers may provide a paper tape label, showing the street name in print and in 

Braille, on the back side of the sign. The print label is not intended to be visible after the sign 

is mounted on the pole. In Figure 14, the label can be seen on the outside of the device. 

Careful inspection reveals that the actual Braille (below the arrow) is indented and all 

symbols are reversed from those shown on the label. This is not readable by touch! Braille 

dots must be raised, not indented. 

In many locations, a person who reads Braille would be delighted to assist in checking the 

labels after installations. If the installation agency is not in contact with someone who reads 

Braille, individuals may be located through vocational rehabilitation agencies, schools for the 

blind, special education departments of public schools, or consumer groups. 26

 

 

26 There are two major consumer groups of individuals who are blind, American Council of the Blind, acb.org, and National 

Federation of the Blind, nfb.org with chapters in many US cities. 

Figure 14 Braille sign installed backwards, with 

manufacturers’ label showing. Label includes street name 

and print of how Braille should look. Braille beneath 

arrow is backwards version of the print version shown on 

label and is indented rather than raised.
Accessible Pedestrian Signals: Installation Details 17 

Issue 11: Good vibrations (vibrotactile indications) 

APS device usability is compromised if the vibrotactile indicator doesn’t vibrate during the 

WALK. The vibrotactile indication provides WALK signal information for pedestrians who are 

both visually and hearing impaired and also may be used by pedestrians who are visually 

impaired (with normal hearing) to clarify or confirm which street’s audible WALK is sounding. 

Where mounting two APS on one pole can’t be avoided, take care to ensure that the 

activation of the vibration of one device doesn’t cause vibration of the device for the 

perpendicular crossing. 

Remedy: The functioning of the vibrotactile indication needs to be carefully checked before 

installation is considered complete and should be a part of regular maintenance checks. 

Troubleshooting: If the arrow does not vibrate during WALK, there are several potential 

areas to check: 

• the basic settings of the device; 

• wiring to the vibrotactile feature; and 

• attachment of the arrow to the device. 

The vibrotactile indication can be turned off in some devices by a setting either on the control 

board or within the PDA device. Check settings to be sure vibration is on. Vibrotactile 

indications may have separate wires to attach in order to enable the feature. If those wires 

are not attached properly, or are attached to the wrong places, or are pinched when reclosing 

the device, the arrow may not vibrate properly. 

If the plate holding the arrow is screwed in, over-tightening the screws can prevent the 

vibration. If the arrow is attached with glue, as found on some manufacturers’ APS, too much 

glue under the arrow can prevent the vibration of the arrow. The arrow needs to be glued 

down, but it also needs to contact the vibrating plate. It seems to work best to put a thin layer 

of glue around the outside edges of the recess, then insert the arrow and align it with the 

direction of travel on the crossing the device indicates. 

If the arrow seems to be vibrating during flashing or steady don’t walk and there are two 

devices on the same pole, the devices are probably touching each other and causing 

vibrations. Installing insulation between the pole and the APS and between the two APS will 

probably remedy the problem. 
Accessible Pedestrian Signals: Installation Details 18 

Issue 12: Audible beaconing 

Audible beaconing -- providing a louder audible WALK signal in order to provide directional 

guidance to pedestrians who are blind -- is not needed at all intersections or during every 

pedestrian phase. If installed at inappropriate locations, or incorrectly adjusted, audible 

beaconing can provide confusing or even dangerous information. 

In the pedhead-mounted APS models installed in the US over the past 30 years, sounds 

were broadcast simultaneously from overhead speakers at each end of the crosswalk and at 

two parallel crosswalks at an intersection. Research now shows that pedestrians are not 

able to use the signal for directional information.27

Even with today’s newer technologies, audible beaconing (or a too-loud signal volume) from 

an APS at a ‘porkchop’ island with a channelized right turn lane may lead a pedestrian who is 

blind to cross the channelized turn lane, thinking it is signalized after hearing the audible 

WALK indication. And at locations where two parallel crosswalks are timed separately, such 

as locations with split phasing, a loud signal can lead a pedestrian to begin crossing with the 

wrong crossing indication. 

Remedy: New types of APS allow calling a louder signal by holding the pushbutton in for 

more than one second, so audible beaconing is a feature that can be called ‘on request’. This 

allows a pedestrian who is blind to decide when a louder signal might be helpful and limits the 

impact of sound on the neighborhood. 

Proposed MUTCD has recommendations for audible beaconing in section 4E.06. 28

Recent research has shown that a louder locator tone during the flashing DON’T WALK, from 

a speaker at the opposite end of the crosswalk from the pushbutton where audible beaconing 

was requested, improves performance in ‘ending within the crosswalk’. 29

 

27 Wall, et al., 2004. 

28 MUTCD NPA, 4E.06 

29Scott, A.C., Barlow, J. M., Bentzen, B.L., Bond, T. and Gubbe, D. (in press) Accessible Pedestrian Signals at complex 

intersections: Effects on blind pedestrians. Transportation Research Record: Journal of the Transportation 

Research Board. 2008.
Accessible Pedestrian Signals: Installation Details 19 

Issue 13: Stub poles 

By installing APS on existing poles without careful evaluation of usability and function, 

jurisdictions may be obviating the benefits such devices provide. In the location shown in 

Figure 15 (a pre-timed intersection), the APS was installed on the available mast arm pole, 

resulting in an installation 

in which the APS volume 

had to be set to be quite 

loud in order to be heard at 

the crosswalk and where 

using the tactile arrow and 

vibrotactile WALK 

indication could result in a 

hazardous crossing. 

In addition, the street 

names are similar -- Penn 

and Tenth -- and it is quite 

difficult to discern which is 

being announced in the 

speech WALK message, 

particularly at the 

crosswalk for crossing 

Tenth (the street to the left 

in Figure 15), where the 

APS is too far from the 

street. 

Remedy: In a similar 

location, shown in Figure 

16, a stub pole was 

installed within five feet of 

the crosswalk in order to 

place the APS in a usable 

location. A signal pull box 

was already in the 

sidewalk area near the 

new stub pole location, so 

concrete work was 

minimized. Stub poles are 

commonly used in some 

jurisdictions. 

Requirements for wiring 

and for mounting poles 

vary in different areas of 

the country. Flexibility in requirements may make it easier to install usable facilities for 

pedestrians. 

Figure 15 APS is located on mast arm pole more than 10 feet outside the 

crosswalk lines. In addition, a fire hydrant is between the crosswalk 

location (and the curb ramp) and the APS

Figure 16 Stub pole was installed to locate APS near the crosswalk
Accessible Pedestrian Signals: Installation Details 20 

Some examples of stub pole installations across the US: 

Figure 17 Examples of stub poles - different materials and installation
Accessible Pedestrian Signals: Installation Details 21 

Issue 14: Inspection of contractor’s work - Beware of field changes! 

While design drawings showed level landings and APS beside the level landings and 

crosswalks, the finished construction did not match the plans. At the location shown in 

Figures 18 and 19, the contractor made some decisions in the field that affected the usability 

of the APS and the curb ramps. 

The APS to cross the street that is on the right in Figure 18 is not located according to the 

plans and the arrow 

points to the curb 

ramp, rather than 

being aligned with 

the direction of 

travel on the 

crosswalk. The 

poor location is 

more easily seen in 

Figure 19, taken 

from across the 

street. A red circle 

highlights where 

the pedestrian 

signal pole was 

supposed to be 

installed. 

By the time the 

designer saw the 

installation, 

however, and noted 

the lack of compliance with 

specifications and with ADA 

requirements, the inspector 

had signed off on the job. 

The contractor and inspector 

both need to understand APS 

installation and use before 

making decisions in the field 

about revisions to plans. 

Figure 18 APS and curb ramps that were not installed as designed

Figure 19 Another view of the same corner. Note shifting slopes 

and cross slopes on the ramps in addition to poor APS location
Accessible Pedestrian Signals: Installation Details 22 

Issue 15: Installation Errors Increase Risk 

This account shows clearly why it’s critical for installers to understand how APS work and 

something about how pedestrians use them -- particularly when the APS is installed in 

response to a user request. 

Some years ago, a city highway agency was contacted

by a pedestrian who requested that an APS be installed 

at an intersection he crossed twice a day, going to and 

from work. He was a colleague of a local orientation 

and mobility instructor, who emphasized the urgency of 

the need in follow-up communications with the DOT, as 

one of the streets was a busy arterial. 

After a lengthy wait, APS were installed for all 

crosswalks of the intersection. On one corner, the APS 

were installed on the wrong poles (as discussed in 

Issue 4) and the tactile arrows had also not been 

installed, but the orientation and mobility specialist 

explained to the user which buttons were intended for 

which crosswalk, and he was able to use them 

satisfactorily. However, after a few months he began 

complaining that the APS were no longer working. 

Technicians checked the devices more than once and 

didn’t find any problems. 

Eventually, the pedestrian and the DOT signal 

technicians arranged to meet at the site. 

Demonstrating the APS, the technician said: “See? The 

button ticks so you know it’s there. When you press the button, the light comes on to let you 

know that it’s working. When the WALK signal begins, you hear a fast ticking sound”. After 

the interpreter signed that information in the pedestrian’s palm, the user shook his head sadly 

and signed back: “I am 100% deaf. I am 100% blind. I need the signal to vibrate.” The 

vibrotactile feature on the APS was not working and the technicians hadn’t noticed. 

After several more attempts to correct the installation and many months of delay that led to 

the filing of an ADA complaint against the agency, the DOT’s ADA coordinator reported that a 

replacement APS from a different manufacturer had been ordered and installed. 

When the ADA coordinator went to check the installation, however, he realized that the APS 

on one corner of the intersection, while installed on two separated poles, were still installed 

on the wrong poles (see Issue #4). He had the mistake corrected; each APS was moved and 

reoriented on the pole close to the crosswalk it controlled. At a subsequent meeting with the 

deaf-blind user and the orientation and mobility specialist at the intersection, the pedestrian 

demonstrated how he used the APS. Using the now ‘wrong’ pedestrian pushbutton, he 

prepared to start his crossing P no one had told him that the APS had been switched to the 

correct poles. Before he could step into the street, he was stopped, and the change of the 

APS was explained to him. He paused, stepped back and looked dismayed, and then 

signed: “If you switch them again, please inform me!” 

Figure 20 Deaf-blind user stands with 

his hand on the original APS to feel the 

vibration in order to know when to 

begin to cross
Accessible Pedestrian Signals: Installation Details 23 

On the other corner, APS for the two different crossings were both installed on one pole, as 

shown in figure 21 and 22. The distance to the crossing (on crosswalk A) results in other 

problems. While there, it was noted that the Flashing Don’t Walk (FDW) signal also was 

extremely short – so short (3 seconds) that it 

was possible for a pedestrian to leave the 

pushbutton and prepare to cross the street 

while the vibrotactile indication was still 

active, but step into the street after the FDW 

had ended. 

This timing issue is complicated by the fact 

that the pedestrian pushbutton for THIS 

crossing is well over 10 feet from the street 

(see figures 21 and 22). It takes this deaf-blind pedestrian nine seconds to get to the 

crosswalk after detecting the vibrotactile signal. After he arrives at the departure curb, it 

takes him 18 more seconds to complete the crossing. 

Because the FDW is much shorter than the pedestrian needs for crossing, he cannot be 

confident of having enough time to cross unless he starts at the beginning of the WALK 

vibration, which causes him unnecessary delay. For this individual and APS location, the 

pedestrian clearance time should be set at 27 seconds. While signal timing here meets 

MUTCD minimums, the engineering of an accommodation like this, installed in response to a 

request, must be based upon individual use (Title II of the ADA requires that jurisdictions alter 

policies, practices and procedures when necessary for accessibility. 30) To complete an 

effective accommodation for this pedestrian, a stub pole should be installed at the second 

crosswalk, so the two APS can be separated and each APS will be located close to the 

crosswalk it controls. 

Another confusing complication here is that while the visual pedestrian signal comes on for 

each cycle, and the APS vibration for crossing the street from one direction comes on for 

each cycle, the APS vibration for the same crosswalk from the other direction comes up only 

 

30 From the DOJ title II preamble at 35.130(b)(7): "Paragraph (b)(7)is a specific application of the requirement under the 

general prohibitions of discrimination that public entities make reasonable modifications in policies, practices, or 

procedures where necessary to avoid discrimination on the basis of disability." See http://www.ada.gov/reg2.html

Figure 21 Orientation & mobility specialist 

approaches two deaf-blind individuals to explain 

the APS (two APS on same pole). One crossing is 

a few feet to the left of the photo; the other is 

about 20 feet away, straight ahead of individual 

with arm on top of APS

Figure 22 When two APS are mounted on an 

existing signal pole, one is poorly located. The 

pushbutton for crosswalk B is near the crosswalk, 

but the pushbutton (and vibrotactile arrow) for 

crosswalk A is a long way from the crosswalk and 

can be difficult to travel.
Accessible Pedestrian Signals: Installation Details 24 

in response to a pedestrian call (button press). This requires the pedestrian to use different 

strategies in timing of his button press at each corner, or he could start his crossing too late in 

the phase. At the corner where the vibration comes on with each cycle, he crosses at the 

beginning of the vibration. At the APS which requires a button press, if it starts to vibrate 

when he presses it, he needs to wait until the next cycle, because it could begin vibrating 

halfway through the walk interval. He must wait until it finishes vibrating, then press it again 

and start to cross as soon as it starts to vibrate for the second time in order to be sure he has 

enough time to cross. This inconsistency is the result of a simple incorrect setting in the APS, 

which needs to be changed so that the APS on each end of the crosswalk work in the same 

manner. 

Small details can add up to big differences in the usability – and safety! -- of APS devices. 

The jurisdiction is still working on correcting the problems, more than 6 years after the APS 

were first requested. Meanwhile, the requestor continues to cross this street to and from 

work, as he’s done hundreds of times since his first request to the city. His risk is his safety; 

the city’s risk is that unreasonable delay may be seen by the courts as discrimination.
Accessible Pedestrian Signals: Installation Details 25 

Summary 

Incorrectly aligned or located APS devices provide ambiguous information in an environment 

in which few other cues may be available. Careful evaluation of every pedestrian signal 

installation is needed to assure that it meets the goals of providing accurate and helpful 

information to pedestrians who have vision impairments, particularly those who may also 

have hearing loss. Whether APS are installed at the request of a local resident at key 

crossings, as Federal funding regulations require, or integrated in new installations under the 

ADA mandate that new construction -- and, to the maximum extent feasible, alterations -- be 

‘accessible to and usable by’ people with disabilities, (title II of the ADA at 35.151, United 

States Department of Justice, 1991), APS must function properly if they are to be useful in 

communicating the information provided to sighted pedestrians by visual pedestrian signals. 

For more information, see resource material developed as part of the National Cooperative 

Highway Research Program Project 3-62: Guidelines for Accessible Pedestrian Signals at 

http://www.walkinginfo.org/aps/ or NCHRP Web Only Document 117A. 

Appendix 

A checklist for evaluation of installations, adapted from Accessible Pedestrian Signals: A 

Guide to Best Practice, NCHRP Web Only Document 117A, is included here as Appendix A. 

Acknowledgements 

Photos in this paper are by the author, Lukas Franck, The Seeing Eye, Rafael Martinez, 

Martinez Engineering Group, Brett Rouillier, District Department of Transportation, Dona 

Sauerburger, COMS, and Lois Thibault, US Access Board. Figures 2, 3, and 6 are from 

Accessible Pedestrian Signals: A Guide to Best Practice, developed for NCHRP Project 3-62. 

Author’s contact information 

Janet M. Barlow, COMS (Certified Orientation and Mobility Specialist) 

Accessible Design for the Blind 

3 Manila Street 

Asheville, NC 28806 

Phone: 770-317-0611 

Email: jmbarlow@accessforblind.org
Accessible Pedestrian Signals: Installation Details- Appendix 1 

Appendix: Checklist for APS Installations (adapted from Accessible 

Pedestrian Signals: A Guide to Best Practice, NCHRP Web-only document 

117A). 

Once installation is complete, the installer should perform the following steps, for each APS 

at the intersection: 

• Check the location of the APS; Is it close to the crosswalk it controls? 

• Check the height of the pushbutton 

• Check the tactile arrow to be sure it is in line with crosswalk 

• Confirm proper functioning of the audible WALK indication 

• Confirm proper functioning of the vibrotactile WALK indication 

• Evaluate and adjust the WALK indication volume 

• Evaluate and adjust the locator tone volume 

• Evaluate and set the sensitivity level of the automatic volume adjustment 

• Check Braille, if provided 

• Check optional features 

• Check audible beaconing 

Check the location of the APS; is it close to the crosswalk it controls? 

Each APS should be close to the crosswalk it controls, preferably in line with the crosswalk 

line farthest from the intersection. APS for other crosswalk should be farther away, and less 

audible. 

Check Height and Location of the Pushbutton 

Confirm that pushbutton height and location conform to specifications and can be reached by 

a person in a wheelchair, from a hard surfaced level landing. 

Check Tactile Arrow 

Check that the tactile arrow is aligned in the direction of travel on the crosswalk. 

Confirm that the arrow points to the street that is controlled by that pushbutton. 

Confirm Proper Functioning of the Audible Walk Indication 

Press the button and wait for the Walk indication. Confirm that it sounds at the proper time for 

the street. 

The Walk indication (tone or speech message) should sound for the duration of the walk 

interval, unless there is a special setting due to a rest in “Walk” situation. 

If the Walk indication is a speech message, confirm that it refers to the correct street and is 

appropriately worded and understandable. 

Confirm that the vibrotactile indications work. 

The tactile arrow or vibrating surface should vibrate rapidly only during the walk interval for 

the street. 

Evaluate and adjust the volume of the Walk indication. 

Stand at the curb or end of the curb ramp at the crosswalk and listen for the Walk indication. 

It should be audible from the crossing location, but it should not be audible across the street. 

Confirm that the Walk indication for each crosswalk sounds closer than the Walk indication 

for the perpendicular crosswalk. 
Accessible Pedestrian Signals: Installation Details- Appendix 2 

Listen through several cycles at times when traffic is noisy and at times when traffic is quiet 

and adjust the Walk indication volume as necessary.

Evaluate and adjust locator tone volume. 

Approach the intersection from both directions along the sidewalk and note when the 

pushbutton locator tone is audible. If there are two pushbutton locator tones at the corner, 

each should be audible. The pushbutton locator tone should be audible 6 to 12 ft from the 

pushbutton or at the building line, whichever is closer to the pushbutton. 

Approach the corner from the crosswalk and note when the pushbutton locator tone is 

audible. The pushbutton locator tone should be audible at 6 to 12 ft (or approximately one 

lane) from the pushbutton. 

Listen through several cycles at times when traffic is noisy and at times when traffic is quiet 

and adjust the locator tone volume as necessary. 

Set the Automatic Volume Adjustment 

Evaluate and set the sensitivity level of the automatic volume adjustment. If volumes are 

adequate in quiet conditions, but do not increase enough or quickly enough when ambient 

noise increases, the microphone sensitivity, or automatic gain control, may need to be 

increased. 

Increase the microphone sensitivity in 10% to 20% steps until the response is as desired. It 

might be necessary to readjust the volume of the locator tone and Walk indications after the 

microphone or “Db over ambient” setting is adjusted. 

Check Braille 

Confirm that braille dots are raised to the touch. If possible, have a person who reads Braille 

confirm that the name on APS is the name of the street that the arrow points toward. 

Check Optional Features, if available 

Pushbutton information message - Press the pushbutton for an extended button press to see 

if the pushbutton information message plays and that it accurately identifies the crossing 

controlled by the pushbutton and that other information, if provided, is accurate. 

Crosswalk map - Confirm that a tactile map accurately represents the crossing features. 

Audible beaconing – If installed, press the pushbutton for an extended button press and 

confirm that the locator tone sound is boosted on that crosswalk during the following 

pedestrian phase (FDW), and walk across the street during the pedestrian phase and 

evaluate placement and aiming of devices for providing sound in the crosswalk area. 

Recheck Device Functioning at a Later Time 

Follow up during the first few weeks after installation, checking device and volume at a 

different time of day to ensure proper functioning. 

Designate a person and phone number to call and report any malfunctioning device. Share 

that information with agencies serving individuals who are blind and with community 

organizations of individuals who are blind. 
Accessible Pedestrian Signals: Installation Details- Appendix 3 

APS Checklist Intersection: 

Begin on SW corner; 

walk around intersection 

clockwise

West crosswalk North crosswalk East crosswalk South crosswalk 

APS 1 APS 2 APS 3 APS 4 APS 5 APS 6 APS 7 APS 8 

APS/pushbutton located 

by crosswalk it controls 

 

Pushbuttons at 42” above 

ground/level surface? 

 

Tactile arrow aimed in line 

crosswalk direction? 

Audible WALK indication 

correct? 

 

Vibrotactile WALK 

indication works? 

 

WALK indication audible at 

crosswalk beginning 

Locator tone volume only 

audible 6 – 12 ft from 

pushbutton? 

Automatic volume 

adjustment functioning? 

Braille correct? 

Optional features – 

pushbutton information 

message correct? 

Optional features – 

crosswalk map correct? 

Optional features - Audible 

beaconing functioning 

properly? 

Comments/notes