RIAS Intersection Study

Intersections are the places in any journey where the traveler is most vulnerable to danger in the form of collisions with passing vehicles which can result in serious injury or death.
At signalized intersections blind travelers who rely primarily on traffic sounds to determine the geometry of intersections, the nature of traffic control, and when it is safe to cross. The usual cue for determining when it is safe to cross at signalized intersections is the surge of traffic beginning to move parallel to the pedestrian's direction of travel. However, at complex, very noisy, or very quiet intersections, it is often difficult to hear the surge of traffic.
Prototype Talking Signs units installed at four signalized intersections in downtown San Francisco were used in this study to provide pedestrian signal information, the location of the pedestrian, and additional information specific to that crossing. The location information is comparable to the information posted on the visual street signs at each intersection. When users near the curb, another message is heard. This "pedestrian crosswalk indicator" message tells users the condition of the pedestrian signal; the particular message depending upon the status of the visual walk/wait sign (see Figure 4). This message can be heard only if the pedestrian is in the crosswalk. Thus the Talking Sign not only tells the pedestrian the current status of the pedestrian cycle but also aids in finding the crosswalk and the direction of the destination corner.

Figure 4. Talking Signs not only gives location information but also tells the pedestrian the current status of the pedestrian cycle, aids in finding the crosswalk, and indicates the direction of the destination corner.

Methods

20 persons having very little or no vision were asked to cross four complex signalized intersections in the Civic Center area of San Francisco under two conditions: with and without information provided by Talking Signs. All crossings were made under normal daytime traffic conditions.

Remote Signage Installation:

A Talking Signs module was attached to the visual pedestrian signal, of four signalized intersection. in San Francisco's Civic Center area. As users came within 150 feet (of an example intersection), their receivers provided them with orientation information: "Traveling East on the zero hundred block of Larkin Street towards Grove Street." Then, as users neared the curb, a "pedestrian crosswalk indicator" message told them the condition of the pedestrian signal. It repeated, for example, "Wait... Grove Street" or "Walk Sign.... Grove Street" through the corresponding signal phase. (A previous focus group, pilot study and survey recommended the term “Walk Sign” instead of “Walk” to avoid the perception of a possibly dangerous instruction or command to begin walking; it only indicates the signage information available to the sighted pedestrian. The cadence of the two-word message “Walk Sign” is also easily distinguished from the single word “Wait” (unpublished report ref. 9).

Figure 5. Users receive “Just In Time Information” regarding the tasks necessary for travel on streets and through street crossings.

Participants also had access to an Auxiliary Message with specific information particular to that intersection. For example : "This is a plus shaped intersection. It is controlled by a fixed timed traffic light in which the walk phase begins with the onset of traffic on Grove. Larkin has two-way traffic on this side of Grove, but one-way traffic coming toward you on the opposite side of Grove. The San Francisco Public Library is across Larkin, and has entrances on both Larkin and Grove."

For this experiment, the message was stored in a palm-sized unit carried on a waist strap. This provided a functional equivalent to a "second channel" originating from the opposite corner (pedestrian crosswalk indicator). If this were to be implemented commercially, the information would be transmitted from the pedestrian signal either as a second channel or on the same channel as the conventional messages.

The experiment took place at one crosswalk at each of four intersections in San Francisco's Civic Center area. Three of the intersections were plus-shaped (four-way), and one was T-shaped (3-way). All the intersections had fixed timed traffic lights (Figure 6).

Figure 6. Twenty-nine Talking Signs units were installed atop pedestrian crossing signals in the Civic Center area of San Francisco.

Subjects:

Participants consisted of 15 males and 5 females, aged 21 to 62, who were independent travelers. All were visually impaired and unable to see pedestrian signals or painted crosswalk lines, or to visually identify the curb line. Most participants considered themselves to be good to excellent travelers. Two considered themselves to be fair to poor travelers but did travel some familiar outdoor routes independently. Two used dog guides as their preferred travel aid, and 18 traveled with a long cane. Four had mild to moderate hearing loss. Participants were either unfamiliar with the crosswalks or did not know which crosswalks were used in the experiment. Nine of the 20 subjects had participated in one or both of the previous projects. (Analysis of the previous experiment had shown no difference in performance based upon experience. Therefore, data from the two groups were pooled.)

Procedure:

Participants received approximately 10 minutes of training in using Talking Signs at a crosswalk that was not subsequently used in the experiment. Participants practiced obtaining information from both the primary and auxiliary messages as they crossed at the practice crosswalk at least twice.

Subjects were guided to a starting location 25 to 50 feet from the street to be crossed. For both Talking Sign and unaided conditions, for the two plus-shaped intersections, the only instruction was "Cross the street that's in front of you." For the T intersection, the instruction was "Find a mid-block crossing and cross the street on your right." For the fourth intersection, participants were asked to "Go to the boarding platform that is in the street in front of you." Participants were divided into two groups, balanced as nearly as possible for reported travel ability, additional disability, and use of a cane vs. a dog guide for travel, and the order of the trials was counterbalanced within and between these groups to minimize practice effects.

In the Talking Signs conditions, participants were asked to listen for identifying information as they approached the intersection. When they reached the intersection and decided that they were well positioned at the crosswalk, they switched to the secondary channel and listened to the Auxiliary message, finally they switched back to the primary channel and kept the on button depressed until they received a message saying "Walk sign, (name) Street." They then listened for traffic to be sure the way was clear, and initiated their crossing. Participants were asked not to use their Talking Signs receivers while they were in the street.

In all conditions, participants were asked to make the crossing as if no experimenters were present who would assure their safety. However, they were free to ask for assistance at any time. After each crossing, they were asked what information they used to determine their heading, what information they used to determine when it was safe to cross, what the shape of the intersection was, and what the traffic control system was at that intersection. They were given no feedback regarding their crossing. They were then guided, by a circuitous route, to the next crosswalk.

During each street crossing the following types of data were collected by an experimenter.

No data were collected on conflicts with turning vehicles, as number of conflicts was not expected to be related to use of Talking Signs information.

Percentages of successful crossings with and without Talking Signs were computed (Figure 7). The definition of "success" varied by measure. For example, in the measure of safety, participants either did or did not begin crossing within the walk interval. If they asked the experimenter to tell them when it was safe to cross, this was statistically treated as missing data for this measure of safety because there was no way to determine when participants would have started crossing in the absence of assistance. In another example, in the measure of Precision "Did the participant end up within the crosswalk at the opposite corner?" participants either did or did not end up within the limits of the marked crosswalk at the opposite corner when they completed their crossing. If they required assistance for the crossing, this was also statistically treated as missing data for this measure. For measures of independence, success meant not requesting assistance or information or requiring experimenter intervention for safety. (“Lack of success” was those trials which were treated as missing data in measures of precision.) For the question regarding the shape of the intersection, participants were expected only to identify intersections as plus- or T-shaped. For the question regarding the type of traffic control, participants were expected only to know that each intersection was controlled by a traffic signal.

Figure 7. Binomial tests for nine measures of street crossing performance with and without the use of the Talking Signs system.

Performance by subject, for each of the nine measures of street crossing success, with and without the use of the Talking Signs system (“TS” versus “non TS”) was tabulated. For each subject, for each measure, if more crossings were successful with Talking Signs than without, subjects were scored +1; if more crossings were successful without Talking Signs than with, subjects were scored -1; if success was the same with or without Talking Signs, subjects were scored 0. For each subject, those scores were then summed. Nineteen of 20 participants were more successful on more measures when using Talking Signs than when not using Talking Signs. One subject had a nearly flawless performance on every measure. This tabulation was the basis for a binomial (step) test which compared each subject with her or himself on each of the nine measures at each of the four intersections, in both the Talking Sign and no Talking Sign conditions. A statistic was computed to determine the probability that differences between performances using Talking Signs and no Talking Signs were significant. The probability of having 19 out of 20 subjects be more successful with Talking Signs than without Talking Signs due to chance alone approaches zero.

There were 80 crossings with Talking Signs and 80 without Talking Signs. On all but one measure, a higher percentage of trials was statistically successful (p <.05) when completed using Talking Signs than without using Talking Signs. The only measure on which there was not a significant difference was the need for assistance in completing a crossing (p <.07). Of interest in this regard, however, is that although participants were told and encouraged to ask for assistance on any crossing, with or without Talking Signs, if they would not normally make such a crossing without assistance, following a number of crossings without Talking Signs information participants said they would not have attempted the crossing if experimenters had not been accompanying them. This remark was not made following any trials on which Talking Signs information was used.

Individual Differences

Four participants reported mild to moderate hearing loss. They showed essentially the same pattern of results as the total group of participants. They may have been slightly more careful and successful travelers. Performance was equal to or better than that of non-hearing impaired participants on safety, precision, independence and knowledge. The two subjects who did not normally travel or cross streets in unfamiliar areas, and did not consider themselves to be good travelers, benefited even more than the rest of the group from Talking Signs. For more complete results including significant subjective reporting, see the complete study report (10).

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