For both intersections, a general trend showed that the older the pedestrian, the longer the crossing time. The authors point out that increasing brightness for this sign does not increase legibility for aging drivers; instead, a redesign of the sign or an enlargement would be needed to enable aging drivers to resolve the level of detail required for recognition. (2007) found that both older and younger drivers may benefit from the implementation of protected left turn phasing at intersections, resulting in less need for hard accelerations to successfully maneuver across oncoming traffic at an intersection (particularly for older drivers), and better lateral control of their vehicles when negotiating intersections. (1995) for pedestrians who complied with the signal, as they tended to walk more slowly than those who crossed illegally. The authors note that the assumed walking speed of 4.0 ft/s leaves almost 15 percent of the total population walking below the assumed speed. He states that a roundabout meets drivers' requirements for simple decision making, and low speed is paramount for safe roundabout operation. Intersections with changing traffic patterns. Exclusive timing is intended to virtually eliminate turning traffic or other movements that conflict with pedestrians while they cross the street. However, this was expected since the rationale behind the use of a gap acceptance model (cf. at night. This compares with 23.7 percent for pedestrians ages 1044 and 13.6 percent for those age 9 and younger. The incorrect responses indicated conservative interpretations of the signal displays which would probably be associated with delay and may also be related to rear-end collisions. As shown in this figure, a gap of 8.0 s affords sight distance for left-turning drivers that equals or exceeds the requirements calculated using the modified AASHTO model for major road design speeds from 20 to 70 mph. The visual/perceptual requirement common to the performance of these tasks is contrast sensitivity: for detecting lane lines, pavement word and symbol markings, curbs and roadway edge features, and median barriers. Reaction times for the larger and brighter lenses (shape coded and 12 RYG) were the shortest, for both groups of subjects. As noted by Harwood et al. The 85th percentile point was approximately 11 s. The oldest group required about 1.1 s longer than the youngest group. The importance of fixed lighting at intersections for aging drivers can therefore be understood in terms of both the diminished visual capabilities of this group and their special needs to prepare farther in advance for unusual or unexpected aspects of intersection operations or geometry. Intersections with unusual geometry (Y or acute angle). Lengths to complete this maneuver vary between 30 and 90 meters. With these values, the total passing sight distance (PSD) can be calculated by simply taking the summation of all three distances. GIF animation: Stopping Sight Distance on Flat Surface (contributed by Oregon State University faculty and students) Flannery and Datta (1996) highlight the fact that modern roundabouts are different than earlier rotaries and traffic circles common in the early 1900's. While the option for dimming on a location-by-location basis should not be excluded, from the standpoint of aging driver needs, there is no compelling reason to recommend widespread reduction of traffic signal intensity during nighttime operations. Traditionally, field of view has not been considered as a parameter that needs to be optimized in lighting system design for intersection applications. Compared to this, for the 65+ age group, when green arrow was shown with green ball, 86 percent of responses were correct, and when green arrow was shown without a green or red ball, 89 percent of responses were correct. Conversely, red and yellow arrows were less comprehensible than circular red and circular yellow indications. Maneuver times for drivers positioned within the intersection versus unpositioned drivers, however, were significantly different. and other roadway features with non-standard stopping sight distance. Stopping Sight Distance. Overall, green arrows were better understood than circular green indications. The average walking speed was 4.25 and 4.74 ft/s (1.3 and 1.45 m/s) for old and young pedestrians, respectively. Van Houten et al. What NCHRP 5-15 makes clear is that the 200 cd intensity requirement for red 200 mm (8-in) signals that appears most prominently in the literature cited above (e.g., Janoff, 1990) is the maintained, in-service performance level for signals in visually simple to moderately complex environments. In general, at mid-block locations, the raised-curb median treatment was associated with fewer crashes than the undivided cross section and TWLTL, especially for average daily traffic demands greater than 20,000 vehicles per day. These losses contribute to slower walking speeds and difficulty negotiating curbs. sight distance profile allows a designer to identify the region of minimum In fact, all of the standards including those for 8-in (200-mm) and 12-in (300-mm) signals, those for red, yellow, and green signals, and those for new and in-service applications are derived from a single requirement for a red traffic signal, established from the work of Cole and Brown (1966). It is common practice to try to enhance the visibility of signals by placing a large, black backplate around the signals. Available evidence suggests, however, that aging individuals have reduced levels of sensitivity to intensity and contrast, but not to color. In The practical consequences of restricted head and neck movement on driving performance at T-intersections were investigated by Hunter-Zaworski (1990), using a simulator to present videorecorded scenes of intersections with various levels of traffic volume and sight distance in a 180-degree field of view from the driver's perspective. The difficulty aging persons experience in making extensive and repeated head movements further increases the decision and response times of aging drivers at intersections. The study authors suggest that these findings provide strong support for the argument that longer sight distances at intersections are required to accommodate older drivers, to give them more time to select a safe gap in which to turn across, enter, or cross traffic. The results of this study showed that intersections with shorter sight distances generally have higher crash rates. This suggests that at stop-controlled intersections, older drivers in particular, older female driversare more likely to collide with speeding vehicles approaching on the major road. Janoff (1990) noted that the evidence to support these ratios is somewhat variable, and support of these recommendations is mixed. Staplin, et al. This is important, because in general, as a vehicle approaches a sign, the observation angle becomes larger, reaching 1.0 degrees at 300 ft, which is roughly legibility distance. It is the minimum distance require within which a vehicle moving at design speed can be stopped without colliding with a stationary object. The overall compliance score across schemes was 89.2 percent; all 5 schemes resulted in successful compliance performance, if the criterion is set to 85 percent. Hostetter, et al. Niederhauser, Collins, and Myers (1997) reported the before and after average annual crash history for the five intersections in Maryland that were converted to roundabouts. Their data consisted of 1,000 police referral forms from the motor vehicle departments of California, Maryland, Massachusetts, Michigan, and Oregon; the forms included observations of incompetent behavior exhibited by aging drivers who were stopped for a violation by law enforcement personnel or were involved in a crash. They should also benefit from carrying out this search without dividing their attention to potential conflicts with pedestrians crossing to the corner island. This is one effect of street lighting. The mean legibility distances across the three intersections and two street sides were as follows for the four sheeting types: Type VII=170 ft; Type IX=172 ft; Type III=142 ft; and Type I=130 ft. Legibility distances were always longer for signs placed on the right side of the street than for those placed on the left. When parallel parking is allowed on the undivided cross section, the undivided cross section is associated with significantly more crashes than the TWLTL treatment. Guide for Reducing Collisions on Horizontal Curves, A At the same time, a relative insensitivity to approaching (conflict) vehicle speed was shown for older versus younger drivers; this result was interpreted as supporting the notion that older drivers rely primarily or exclusively on perceived distancenot time or velocityto perform gap acceptance judgments, reflecting a reduced ability to integrate time and distance information with increasing age.