Effects of APS on specific crossing tasks


Since it is known that pedestrians with visual impairments have difficulty with many of the tasks that, taken together, comprise street crossing, it would be desirable to think that APS improve all measures of crossing at signalized intersections. To determine the extent to which this is true, a number of research projects have obtained objective data comparing street crossing with and without APS on one or more of the following measures.

Projects that have already been mentioned are: SKERI research; NEI Portland pre-post; Uslan et al, (1988); Marston and Golledge, (2000) and Williams et al. (2005).

There are several additional studies that shed light on this topic. As part of NEI research, in three different experiments Wall, Ashmead, Bentzen and Barlow (2004), blind and blindfolded sighted participants made crossings at a simulated intersection, in the presence of recorded traffic sound to determine the effect on crossing accuracy with signals comprised of bird calls, percussive "toks," a click train, or a female voice. The signals, all of which were mounted at a height of eight feet, came either simultaneously from both ends of a crosswalk (typical practice), alternated from one end to the other, or came from the far end of the crosswalk only. These researchers also compared crossing accuracy when signals came from two parallel crosswalks (typical practice), or from a single crosswalk. A further comparison was between WALK signals with a typical 7sec. duration versus a seven sec. WALK signal followed by a locator tone.

Hulscher (1976) reported an estimate by Leith (personal communication) comparing starting delay pre- and post-APS installation.

Wilson conducted a pre- and post-APS installation study of behavior of adult, non-disabled pedestrians at one intersection.

Further, the research undertaken for NCHRP 3-62 (REF final report chapters) contributed to the understanding of the effects of APS on specific crossing tasks.

Results of Research

Locating the crosswalk

SKERI research found that starting crossing from within the crosswalk increased from 70% to 97% with use of the APS.

NEI Portland pre-post research found significant increases in participants' ability to begin crossings from within the crosswalk at locations where pushbutton use was required, and pushbutton locator tones were installed. Pre-installation, 77% of crossings began from within the crosswalk; post-installation, 97% of crossings began within the crosswalk, indicating that locating the crosswalk was significantly improved by the presence of pushbutton-integrated APS. (Barlow, Bentzen, Bond and Gubbe, 2006)

Orientation (Aligning to cross and maintaining alignment while crossing)

APS have some affect on aligning to cross, but results have not been as positive as desired.

On 48% of crossings in SKERI research, where APS information was not available, blind pedestrians were not facing directly toward the opposite corner when they started their crossing; they were facing somewhat toward or away from the center of the intersection. With the use of receiver-based APS, participants were well aligned when beginning 80% of crossings.

However, in NEI Portland pre-post research, alignment showed only a very small trend toward improvement, with 70% of independent crossings starting from an aligned position pre-installation and 84% post-installation.

NEI research (Wall, et al, 2004) found the presence of a locator tone during the second half of the crossing had a positive effect on alignment.

In the NCHRP 3-62 research on device features, statistical analyses revealed no differences in orientation attributable to device in Tucson, and only a few minor differences in Charlotte. These differences are easily explained by unique characteristics of the given intersection or pole placements, and taken together with the lack of findings in Tucson, suggests that none of the differences in APS device features on different manufacturer's APS had an important impact on pedestrian orientation. (See NCHRP 3-62 Final Report, and Bentzen et al, in press.)

Various means of beaconing and providing directional information to blind pedestrians are being investigated in the NEI research, including increasing the volume of the locator tone and providing it from a directional speaker, and an orientation tone which involves increasing the volume of the locator tone on the opposite end of the crosswalk, before the crossing interval, in response to a request. Data collection and analysis of results from these experiments are not complete.

Using pushbuttons

Data reported in NEI pre-APS installation testing (NEI-2 cities, NEI-3 cities) indicated that blind pedestrians typically didn't search for and use pedestrian pushbuttons at unfamiliar intersections. In Portland, after installation of APS with locator tones (NEI Portland pre-post), participants were not instructed to use the pedestrian pushbuttons, nor were they provided with instruction about the fact that pushbuttons were needed to call the WALK interval at some of the crossings. However, the addition of pushbutton locator tones and the knowledge that an APS might be installed resulted in participants looking for the pushbuttons on over 98% of crossings, although looking for the pushbutton did not always result in finding and using the correct pushbutton. Participants independently looked for and used the pushbuttons on 93% of the crossings after pushbutton locator tones were installed. In the pretest situation, pedestrians had looked for and used pushbuttons on only 16% of crossings.

NCHRP 3-62 research (See NCHRP 3-62 Final Report and Bentzen et al. in press) reported that while pedestrians who are blind do not typically use pushbuttons when making unfamiliar crossings, after being made aware of the function of the pushbuttons to call the WALK interval, and hearing the demonstrator locator tones, 100% of participants in Tucson and Charlotte searched for the pushbutton. Participants in both cities said they used the locator tone when locating the pushbutton on most trials, regardless of device. However, presence of a pushbutton locator tone did not guarantee that participants would find and push the correct pushbutton. Errors in finding the correct pushbutton were reported, leading to recommendations for instruction in understanding and using tactile arrows, as well as maintaining orientation while looking for pedestrian pushbuttons.

Initiating the crossing

APS have been found to positively affect measures of delay in beginning to cross, starting crossing during the WALK interval, and completing crossings before the onset of perpendicular traffic.

Delay in beginning to cross

Hulscher (1976) cites a personal communication from Leith (1975) in which Leith estimated that, following APS installation, delay in beginning crossings was reduced an average of 2-3 seconds for all pedestrians.

Wilson (1980) in a pre- and post-APS installation study of adult non-disabled pedestrian behavior at one intersection., found the following results.

Williams et al. (2005) found that mean latency in beginning crossing without APS was more than 5 seconds, which was reduced to 2.2 seconds with a receiver-based APS device with a tone WALK indication and 3.8 seconds with a pushbutton-integrated APS using speech messages.

In NEI Portland pre- post research, in 144 crossings pre- and post-APS installation at two intersections in Portland, Oregon, the weighted mean starting delay for blind pedestrians without APS was 5.1 seconds, and after APS installation, the delay was reduced to 2.9 seconds. Uslan et al, (1988) also found significant differences between speed of crossing at control intersection and intersections where APS were installed; crossings at locations with APS were completed faster.

Williams et al. (2005) assessed participants on total number of signal cycles missed before crossing. Without APS, mean wait time was almost 2 full cycles, while with either type of APS, the mean wait time was just over a half a cycle.

In NCHRP research different WALK indications have been found to affect latency to begin crossing. (See NCHRP 3-62 Final Report, Chapter 2,).

Starting during WALK, and completing crossing before the onset of perpendicular traffic

In SKERI research, participants began crossing during the WALK interval on only 66% of crossings without APS, but on 99% of crossings with APS.

In NEI Portland pre-post research, without APS the pedestrian-actuated crossings were highly problematic for pedestrians who are blind. Pre-installation, participants began crossing during WALK on only 25% of crossings. Post-installation, there was dramatic improvement in participants correctly determining the appropriate time to start crossing with 84% of crossings initiated during WALK. Similarly, participants completed crossing after the onset of perpendicular green on 50% of crossings pre-installation with a significant decrease, post-installation, to 12% of crossings completed after the onset of perpendicular green.

Furthermore, only 77% of decisions about when to start crossing were made independently pre-installation as opposed to 95% post-installation. Pre-installation, the total number of crossings where the individual independently determined a start time and actually began crossing during the WALK interval was less than a quarter of crossings. Post-installation, with the addition of the APS, there was a significant increase both in independence and in beginning to cross at the appropriate interval.

For crosswalks where the pedestrian phase was on recall, the APS sounded at the beginning of the WALK interval, regardless of whether the pushbutton was used or not. The WALK indication only sounded for the first seven seconds of the WALK interval, unless the pushbutton was pushed again. Pre-installation, 70% of independent crossings began during the WALK interval; post-installation, this increased to 100%.

Marston and Golledge (2000) found that at crossings without APS, almost half (48%) of the participants attempted to cross during the steady DONT WALK interval, a time recorded as unsafe by the researcher. With access to the pedestrian signal information provided by APS, no participant started crossing at an unsafe time.

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