Most studies of sign legibility report legibility distance and the letter height of the stimulus; dividing the former measure by the latter defines the "legibility index" (LI), which can serve as a common denominator upon which to compare different studies. The crash rate at the 21 study intersections decreased by 51 percent for total crashes and by 38 percent for ran-STOP-sign crashes. Intersections where the character or speed of the road changes, such as at entry points to a community or at junctions where a bypass road connects to an arterial. To place this discussion in context, it should also be noted that traffic signal recommendations for different sizes, colors, and in-service requirements have, in large part, been derived analytically from one research study conducted by Cole and Brown (1966). Aging pedestrian problem behaviors include a greater likelihood to delay before crossing, to spend more time at the curb, to take longer to cross the road, and to make more head movements before and during crossing (Wilson and Grayson, 1980). At nighttime, there was a significant interaction effect between font and sheeting material, such that the Clear 112 font produced significantly longer legibility distances (22 percent longer) than the Series E(M) font, using the encapsulated lens sheeting. Case C: Intersections with Yield Control. Where R = 5730/D S = Stopping sight distance (ft) R = Radius of the curve (ft) All intersections were controlled by traffic signals with yield control on the three channelized intersections. Researchers examining the State crash records of 53 aging drivers found that those with restrictions in their "useful field of view," a measure of selective attention and speed of visual processing, had 15 times more intersection crashes than those with normal visual attention (Owsley, et al., 1991). 1200 New Jersey Avenue, SEWashington, DC 20590 The protected-only/leading and protected/permissive schemes are known as "leading," and the protected-only/lagging and permissive/protected are known as "lagging" schemes. (1982). Operationally, vehicles in the opposite left-turn lane waiting to turn left can also restrict the (left-turning) driver's view of oncoming traffic in the through lanes. TheMUTCDhas adopted similar wording, which is shown as part of Recommendation C of Design Element 16. Persuad, et al. If curb radii are too small, lane encroachments resulting in traffic conflicts and increased crash potential can occur. The SSD is the distance required, at a given speed, for a In one study, approximately 85 percent of the pedestrians age 60 and older required a minimum gap of 9 s before crossing the road, while only 63 percent of all pedestrians required this minimum gap size duration (Tobey, Shungman, and Knoblauch, 1983). Staplin, et al. Additionally, all intersections were controlled by traffic-responsive semi-actuated signals, and all left-turn maneuvers were completed during the permissive left-turn phase at all study sites. Alternatives 3 and 4 both are described by corner curb line geometries offering ease of turning and good visibility; however, isolated responses to the truncated corner geometry (Alternative 4) indicated concerns that providing too much room in the right-turn path might result in a lack of needed guidance information and could lead to a maneuver error, and that it could be harder to detect pedestrians with this design. One of the most common uses of channelization is for the separation of left-turning vehicles from the through-traffic stream. (1982) study cited earlier, Hauer (1988) stated that because channelization in general serves to simplify an otherwise ambiguous and complex situation, the channelization of an existing intersection might enhance both the safety and mobility of aging persons, as well as enhance the safety of other pedestrians and drivers. Potentially unsafe interpretations were found for red arrow displays in protected-only operations. In this study, 19 drivers ages 25 to 45, and 20 drivers ages 65 to 85 viewed visual representations of actual intersections on urban and residential streets in Gainesville, FL, and made braking, accelerating, and steering responses using controls integrated into an actual vehicle. This investigation includes a series of laboratory and field studies to determine performance-based signal requirements for traffic signal intensity, intensity distribution, and related photometric parameters using a subject population that oversamples aging drivers (Freedman, Flicker, Janoff, Schwab, and Staplin, 1997). Maneuver times for drivers positioned within the intersection versus unpositioned drivers, however, were significantly different. The pedestrian clearance time should be sufficient to allow a pedestrian crossing in the crosswalk who left the curb or shoulder at the end of the WALKING PERSON (symbolizing WALK) signal indication to travel at a walking speed of 3.5 feet per second to at least the far side of the traveled way or to a median of sufficient width for pedestrians to wait. In this study, the average walking speed of the older pedestrians was 2.8 ft/s, with a standard deviation of 0.56 ft/s); the average speed of the younger pedestrians was 4.2 ft/s, with a standard deviation of 0.56 ft/s). To compensate for this, it would appear necessary to assume a longer required visibility distance, which would result in an increase in the signal intensity required. Controlled field studies and simulator studies involving aging drivers have confirmed that brake reaction times to unexpected hazards (e.g., a barrel rolling into the road in front of the driver, a vehicle turning in front of a driver who is traveling straight through an intersection) are not significantly different as a function of age, and that virtually all response times are captured by the current 2.5-s AASHTO design parameter for brake perception-response time (Lerner, et al., 1995; Kloeppel, et al., 1995). Kihlberg and Tharp (1968) showed that crash rates increased 35 percent for highway segments with curved intersections over highway segments with straight intersections. All subjects had a visual acuity of at least 20/40. of the hill. Warrants for traffic signals are thoroughly described in theMUTCD. However, passive detection also can be used to detect pedestrians within the crosswalk that may need more time to complete their crossing maneuver.
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