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It is interesting that the average increase in yielding from baseline to a two-beacon system was 18.2% to 81.2%. The introduction of the four-beacon system was also associated with an average increase in yielding to 87.8%. This increase from two to four was found to be statistically significant (Table 1). It may be that these increases from two to four systems are due to the rapid-flash sequences and their visibility to the motorists occupying the inside lanes. That is, the middle lanes in which the motorists are more likely to see the median devices rather than those placed near the curb.
The increase in yielding distances is also an important effect. With motorists yielding at further distances, the chance that a pedestrian may be struck by a motorists due to the inability to see the pedestrian and vice-versa due to a yielding vehicle is greatly reduced. An increase in yielding distance decreases the probability of a multiple threat. The amount of yielding occurring at >100ft. more than doubled over baseline during the four-system treatment. It was often observed that many of the motorists yielded at distances much greater than 100 feet upon activation of the rapid-flash devices. Since the research sites were only marked up to 100 feet, there was not a way to accurately record such distances. It was reported that it sometimes appeared that motorists were yielding at twice the distance as from the crosswalk to the 100ft. flag. This would be distances up to, and possibly in excessive of, 200 feet. It is suggested that this also occurs due to the visibility of the lights at such great distances. These distances were also reported during the two-system treatments, but not as often.
The increases in yielding percentages and the yielding distances are, as should be, associated with a decrease in the number of vehicle passes, or attempts. This may also be due to the fact that, when activated, the signs are visible to all motorists and not only those in the direct field of vision to the pedestrian. However, it may sometimes be the case that a larger vehicle, such as a panel or delivery truck, blocks the view of a driver in a smaller vehicle.
The efficacy of the standard overhead beacon system appears to be minimal at best. There was only a small increase in yielding compliance over baseline with the activation of the standard lighting system. The rapid-flash system was installed and evaluated at the same location. The rapid-flash system produced yielding percentages of 81.5% (two beacon-system) and 88.7% (four beacon-systems). Since these numbers were recorded at the same site with the only differences being the device used, it is assumed that this is due to the rapid-flash system being more visible and in the line-of-site to the motorists, as opposed to being highly elevated.
The strongest data recorded for the effectiveness of the rapid-flash system were the data collected during nighttime observations. These data came closest to approaching a full 100% yielding compliance. During some observation periods, 100% was recorded. In fact, it was recorded during four straight observation periods during four-beacon treatment. That is 80 consecutive street crossings in the presence of automobiles with total yielding compliance. The higher yielding compliance can probably be contributed to the fact that the LED lights become much more visible and salient at night.
The LED lights offer advantages, other than those produced in this study, when used instead of the conventional lighting sources (i.e., halogens or strobes). For one, LED lights require a very small amount of power to operate when compared to other forms of lighting. Second, LED's can be activated and deactivated very quickly, referred to as their "ramping" speed, within their lighting sequences. This means that there is no carry-over effect from one flash to the other. This eliminates stop motion action and allows for greater conspicuity. Stop motion action is often encountered when one is in the presence of a strobe light.
The Society of Automotive Engineers (SAE) has researched the different uses of ground vehicle LED lighting and their effects for over 20 years. They have suggested that an optimum flash rate is between 60-120 flashes per minutes. This suggested flash rate is an attempt to have the lighting as perceivable as possible. The LED lighting sequence of the rapid-flash systems in this study produced a combined 390 flashes per minute for each set of forward facing lights. Since each set included two light sources flashing in a wigwag pattern, this means that there were actually only 190 flashes per minute, 60 flashes more than suggested by SAE. However, it should be noted that a flashing light is only perceived as being a steady lamp as they approach 1200 flashes per minute. It may be assumed that the separation between the lights allows for a slower perception of the flash rate of each individual light, thus, allowing a slightly higher than recommended flash rate to be effective. However it is also suggested that a study should be conducted with a slower, SAE recommended, flash rate. The Society of Automotive Engineers, in their extensive past, has conducted and concluded on several other properties of lighting and human perception. 1
It is suggested that a major factor in the increases in yielding compliance is due to the combination of the rapid-flash lights and the signage they are attached to. If the lights were installed alone, the yielding percentages would be expected to decrease. Without a message attached to the lights (pedestrian silhouette), the lights themselves convey no useful information. It is often the case with emergency vehicles especially, that too many lights are used with too little direction (i.e., information) and that this may actually be counterproductive (Wells, 2006).
The type of textual prompt associated with the flashing beacons should be analyzed. The message is explainable in that the sign serves as a visual stimulus for, basically, a generic representation of a crossing pedestrian. It can be assumed that the majority of drivers have all had some past exposure and reinforcement history with this type of sign. That is, drivers have learned that the signs are usually placed at pedestrian crosswalks and that yielding occurs at these places. Once the sign is attended to, there are then a set of contingencies that define the desired behavior and possible outcomes. It may be that seeing the sign is then associated with regulations requiring the yielding of motorists to pedestrians. Therefore, the sign may be serving as a rule/law to yield for pedestrians. It should be noted that during the approach some of the drivers are exposed to the "Yield Here…" and "State Law" signs (Figure 2). These signs state the rule. Kudadjie-Gyamfi and Rachlin (2002) state that "When rules signal current contingencies behavior usually adjusts faster to those contingencies than when no rules are provided." The signs do not directly state any outcome for yielding, or not, this could provide some explanation for lower yielding if the attached pedestrian signage and/or "Yield Here…" signs were removed. There would be no stimulus associated with or explaining what behavior is expected and the desired behavior would eventually be a result of multiple trials. "When provided as information about contingencies, rules work as verbal prompts that abbreviate the time and effort that are required by a full shaping process" (Ribes-Inesta, 2000).
The results of this study clearly demonstrate the rapid-flash pedestrian crossing aids greatly increase driver-yielding behavior, as there were marked increases in yielding above the percentages reported during both baseline and the standard yellow flashing beacon. These are also the highest yielding levels reported for any crosswalk system that does not include a red indication. As a result of these findings, and the reduced cost of this type of system I have adjusted the warrant for the ITS crosswalk in the Pedestrian Crossing Task Order produced for the city of St. Petersburg. Because the cost of the system is a third to a quarter that of competing systems that include a mast arm I have revised the warrant numbers conservatively by half. The revised warrant document is included in Appendix 1.
1 Blue Advancing-Red Receding phenomenon. At night, the eye perceives high frequencies (blue/violet) as moving towards the observer while lower frequency colors (red) appears to be moving away. This aids in support of amber because there is no confusion of the placement of the lights relative to the automobile's speed. Also, nearly eight (8) percent of males have one of the three most common forms of color blindness while only about .5 percent of females exhibit the same.
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United States Department of Transportation - Federal Highway Administration |
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