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Federal Highway Administration Research and Technology
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Publication Number: FHWA-HRT-10-043
Date: September 2010
Effects of Yellow Rectangular Rapid-Flashing Beacons on Yielding at Multilane Uncontrolled Crosswalks
CHAPTER 6. EXPERIMENT 4
Participants in experiment 4 drove through the crosswalk at 4th Street and 18th Avenue S in St. Petersburg, FL. This location has four through lanes at the crosswalk with a refuge island in the center median. The location has a posted speed limit of 35 mi/h and an ADT of 17,657.
The treatment in this experiment is identical to that of experiment 1. A standard pedestrian warning sign with two RRFBs with the same light positioning, timing, and sequence was used. Each unit was dual indicated, with LEDs on the front and back. Each side of the beacon flashed in a wig-wag sequence (left light on followed by the right light on). Combined, the two LEDs flashed 190 times in the wig-wag sequence during a 30-s cycle. The devices were updated with Direct Aim® lighting and the momentary light bar (MLB).
Direct Aim® lighting angles the LED lights of preexisting units so that the lights, when activated, do not flash parallel to the roadway but rather flash at an angle that places oncoming traffic lanes in the direct path of the light (see figure 7). In the figure, the arrows on the left panel show perpendicular lighting, while the arrows on the right panel highlight Direct Aim®. This device was developed to accommodate the sensitive directivity of LED lights. That is, LED lights have a small angle of maximum visibility and effect. While new LED lighting systems mounted on emergency vehicles are parallel to the roadway and the vehicle, they remain effective in their purpose. The reason for this may be that their purpose is to alert all of those directly in front of them to pull off to the side of the roadway. However, it would seem impossible to place the RRFB lights directly in the path of oncoming traffic. The MLB device is an addition to Direct Aim® lighting. The MLB attaches below the Direct Aim® and is activated on a delay circuit. The delay allows any vehicles in close proximity to the activated crosswalk to clear the crosswalk. Once this has occurred, the MLB activates with a horizontal arrangement of intensely bright LEDs. After a moment, the MLB lights fade out.
In this study, an alternating treatment design was employed to record driver yielding percentages in an evaluation of two devices in an effort to further increase driver yielding to pedestrians at a single midblock crossing. The alternating treatment design was chosen due to its ability to evaluate multiple treatments while offering experimental control. This is accomplished by rapidly alternating between two or more different treatments in succession after an initial stable baseline has been achieved. The design allows for the alleviation of any possible confounding or nuisance variables.(13) First, baseline data were collected by having staged pedestrians (researchers) cross as the drivers' yielding behavior was recorded for three datasheets, each consisting of 20 crossings. After this, data were collected on the preexisting RRFB device for a total of 70 crossings following the baseline at 7, 30, 270, and 365 days. The third stage involved the installation of Direct Aim® LED lights along with an MLB to the RRFB.
Figure 7. Photo. Perpendicular lighting (left panel) and Direct Aim® lighting (right panel).
The MLB device was installed with a cutoff switch to allow for a quick transition between Direct Aim® and Direct Aim® plus MLB. A coin flip was used to decide which device was to be evaluated first. After Direct Aim® was evaluated for 20 crossings, the switch was flipped, and the MLB was evaluated for 20 more crossings. This collection procedure was reproduced 5 times per condition, producing 100 crossings per condition.
A z-test for proportions was used to test for differences. The percentage of drivers yielding in the RRFB with the Direct Aim® condition did not differ from the percentage yielding in the Direct Aim® plus MLB condition at the 0.05 level (z = 0.43 with 66.6 percent confidence level one tail test). However, the RRFB with Direct Aim® was associated with higher yielding than the parallel aim RRFB at the 0.05 level (z = 1.74 with 95.9 percent confidence level one tail test).
The percentage of drivers who yielded to pedestrians during the baseline condition was zero percent. The average yielding compliance 7 days after RRFB installation increased to 33 percent. Yielding compliance continued to increase to 72 percent 30 days after installation. Average yielding compliance was 69 percent after 180 days and remained unchanged 270 days after installation. Yielding compliance 365 days after installation averaged 80 percent (see figure 8). The average yielding compliance during the duration of the RRFB with perpendicular lighting was about 80 percent.
The change from perpendicular LEDs to Direct Aim® lighting produced an average increase of 89 percent. Sessions including the MLB produced an average of 86 percent. These averages included 100 crossings per condition.
Figure 8. Graph. Yielding compliance for experiment 4 located at 4th Street and 18th Avenue S in St. Petersburg, FL.