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18 the pedestrian crossing. Many installations have used both over- head and side-mounted beacons. The effectiveness of the flash- ing beacons in general, however, may be limited on high-speed or high-volume arterial streets. For example, overhead flashing beacons have produced driver yielding behavior that ranges from 30 to 76 percent, with the median values falling in the mid- 50 percent range (26, 36-38). The evaluations did not contain enough information to attribute high or low driver yielding val- ues to specific road characteristics. The field studies conducted in this TCRP/NCHRP project found a similarly wide range of motorist yielding values (25 to 73 percent), with the average value for all flashing beacons at 58 percent. The analysis of site conditions and traffic variables also found that traffic speeds, traffic volumes, and number of lanes have a statistically signifi- cant effect on driver yielding behavior on arterial streets. Figure 8. Pedestrian-activated overhead flashing beacon. In-Roadway Warning Lights diluted their effectiveness in warning motorists of conditions. As a specific design case of flashing beacons, in-roadway Flashing beacons have been installed in numerous ways: warning light installations have proliferated in their 10 years of existence. Their use originated in California and Washington At the pedestrian crossing, both overhead and side mounted; State but has spread to numerous other places in the United In advance of the pedestrian crossing, both overhead and States (see Figure 9). In-roadway warning lights are mounted in side mounted; the pavement near the crosswalk markings such that they typi- In conjunction with or integral within other warning signs; cally protrude above the pavement less than 0.5 in (1.3 cm). As and with flashing beacons, the experience with in-roadway warning In the roadway pavement itself (see next section on in- lights has been mostly positive, with a few negative results. roadway warning lights). Many early and some current equipment designs for the in-roadway warning lights have been problematic. Some of The operations for flashing amber beacons may also vary, the problems encountered are as follows: including the following: Snow plows have damaged the flashing light enclosures, Continuous flash mode; Light lenses have become dirty from road grit and have Pedestrian activated using manual pushbuttons; required regular cleaning, and Passive pedestrian detection using automated sensors (e.g., Automated pedestrian detection has not operated effectively. microwave or video); and Different flash rates, sequences, or strobe effects. The experience with flashing beacons has been mixed, as would be expected when they have been installed in numerous different ways. Several studies have shown that intermittent (typically activated using a manual pushbutton or automated sensor) flashing beacons provide a more effective response from motorists than continuously flashing beacons (36, 37). These beacons do not flash constantly; thus, when they are flashing, motorists can be reasonably sure that a pedestrian is crossing the street. With pedestrian activation, special signing may be necessary to ensure that pedestrians consistently use the pushbutton activation. Alternatively, automated pedestrian detection has been used with some success, but typically requires extra effort in installation and maintenance. Overhead flashing beacons appear to have the best visibility Figure 9. In-roadway warning lights and to motorists, particularly when used both at and in advance of supplemental signs and beacons in Austin, Texas.