Given the positive experience of some practitioners who are early adopters of this treatment, further FYA research is a high priority. At YIELD signs, more than half of the crashes were rear-end collisions, while more than half of the crashes at STOP signs were angle collisions. The authors recommended that in a 5-section horizontal display, the green arrow and red ball should not be illuminated simultaneously. As noted earlier, studies performed to date to evaluate the safety performance of roundabouts have not included driver age as a variable. The use of an advance street name plaque (W16-8) with an advance warning crossroad, side road, or T-intersection sign (W2-1, W2-2, W2-3, and W2-4) provides the benefit of additional decision and maneuver time prior to reaching the intersection. Known implementations of this design include an intersection in Charlotte, NC, and several intersections in Florida and Texas. All intersections were located within a growing urban area where the posted speed limit was 35 mph. The improved design was associated with lesser side forces and fewer deviations from the idealized curved path during the turn, indicating improved lateral control and greater vehicle stability. Previously, however, Lunenfeld (1977) cited the considerable range of night background luminances that may occur in concluding that in some brightly lit urban conditions, or where there is considerable visual noise, daytime signal brightness is needed to maintain an acceptable contrast ratio. Zegeer, Opiela, and Cynecki (1982) conducted a crash analysis to determine whether pedestrian crashes are significantly affected by the presence of pedestrian signals and by different signal timing strategies. (1995), parallel and tapered offset left-turn lanes are still not common, but are used increasingly to reduce the risk of crashes due to sight restrictions from opposite left-turn vehicles. To ensure that the signs recommended in the laboratory perform as intended, they should be tested in the field, and therefore, no recommendation for their implementation is made for thisHandbook, and the study findings should be considered as preliminary. Later, older drivers (as well as their younger counterparts) were shown to benefit from redundant signing (Staplin and Fisk, 1991). For design purposes, the authors concluded that a mean value of 2.5 s and an 85th percentile value of 3.75 s would be appropriate. Raised curbs that are unmarked are difficult to see, especially in terms of height and direction, and result in people running over them. The older drivers were more likely to be turning left or starting from a stop than their younger counterparts. Taking the indicated value for the least capable 5 percent of 75-year-olds into account, as well as the prior field evaluations, a contrast requirement of 3.0 for pavement markings appears most reasonable. Information on signal intensity requirements that will accommodate road users with age-related vision deficiencies is provided by NCHRP Project 5-15, Visibility Performance Requirements for Vehicular Traffic Signals. A study by Markowitz, et al. A reduction in legibility distance of 10 to 20 percent should be assumed when signs are not fully reflectorized. An interaction effect between age and speed showed that for the lower approach speed scenario (25 mph), the older drivers accepted larger gaps (females =10.99 s; males 8.76 s) than the young drivers (females =7.56 s; males = 6.35 s) and middle-aged drivers (females = 6.97 s; males = 6.60 s). In contrast, research conducted by Lerner, et al. (1997) found no significant differences in maneuver time as a function of age for the drivers turning left at the four intersections studied (which had distances ranging from 84 to 106 ft). The increased mobility exhibited by the younger drivers at the channelized right-turn lane locations (controlled by YIELD signs) was not exhibited by old-old drivers, who stopped in 19 of the 20 turns executed at the channelized locations. The results of these calculations for alternate values of G, beginning at 7.0 s, are plotted against the required sight distance calculated using the modified AASHTO formula [1.47V(J+ ta); where J=2.5 s and ta is obtained from Table IX-33 in the 1994Green Book] inFigure 73. ISD for a vehicle on a stop-controlled approach on the minor road to accelerate from a stopped position and turn left onto the major road. (2007) recommended the use of the roundabout advance warning sign, augmented with a symbol representing the center island, as shown inFigure 82. Retroreflectance values were calculated based on the luminance levels needed to accommodate 67, 85, and 95 percent of the population of U.S. drivers. Left-turn channelization separating through and turning lanes may, because of its placement, constitute a hazard when a raised treatment is applied, especially on high-speed facilities. Of particular importance is that the reaction times of the normal color vision drivers over age 50 (n=15) compared closely to those of color-vision-deficient drivers (n=50). To emergency and construction vehicles, when lights are flashing. Next, there has been increasing interest in the use of durable fluorescent sheeting for highway signs, because of its increased conspicuity over standard highway sign sheeting, under daytime conditions. These losses contribute to slower walking speeds and difficulty negotiating curbs. These configurations were most often associated with low-speed, high-volume urban locations, where intersection negotiation requires more complex decisions involving more conflict vehicles and more visually distracting conditions. One set of intersections included roadways that met at a 90-degree angle (improved) and roadways that met at an angle less than 75 degrees (unimproved). McKnight and Stewart (1990) identified the task of positioning a vehicle in preparation for turning as a critical competency. For multilane approaches to roundabouts, signs should be designed to assure that drivers choose the proper lane for their destination before reaching the roundabout, and once in that lane, they should be able to circumnavigate the central roadway of the roundabout and exit to their destination without having to change lanes while in the circular roadway of the roundabout. Failing to yield, disregarding the STOP sign, and inattention were most often cited as the contributing factor for the two older groups. It is important to note that, whether luminance is measured in metric or English units [candelas per square meter (cd/m2) or footlamberts (fL)], contrast is a dimensionless number; thus the present recommendations as well as the calculation of contrast level are independent of the unit of measure. The biggest problem with turn-only lanes reported by group participants was that there is not enough warning for this feature. Freedman, Davit, Staplin, and Breton (1985) conducted a laboratory study and controlled and observational field studies to determine the operational, safety, and economic impact of dimming traffic signals at night. The Optional Movement Lane Control Sign (R3-6) is required to be located in advance of and/or at the intersection where the regulation applies. Observations of 696 pedestrians divided among three age groups (age 30 and under, ages 3150, and age 51 and older) showed that the oldest group stood the farthest from the curb, that they stood even farther back under nighttime conditions, and that aging females stood the farthest distance from the curb. 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. At the same time, providing drivers with more detailed information about what to expect when they reach the roundabout should enhance the operational safety of roundabouts for aging drivers in particular, as well as the general population of drivers, without any unintended consequences. 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. Although the sign is more expensive than standard signs and pavement markings, the authors concluded it may be justified in situations where pedestrian protection is critical during certain periods (i.e., school zones) or during a portion of the signal cycle when a separate, opposing left-turn phase may conflict with an unsuspecting RTOR motorist. The study included a review of past studies (many of which were previously discussed) and the collection of additional observational data in six cities throughout the U.S. Knoblauch, et al. For protected-only operations, the green arrow (with circular red for through movement) was correctly answered by approximately 75 percent of drivers. ISD for a vehicle on any approach determined by the location of the first vehicle on all other approaches. At intersections with a "Yield" sign, you must: - DMV Written Test Mace (1988), in his work on minimum required visibility distance (MRVD) for highway signs, noted the following relationships: Either the letter size or the LI may be manipulated to satisfy the MRVD requirement, which specifies the minimum distance at which a sign should be read for proper driver reaction. Injury crashes decreased from 4.3 per year to 0.3. Approximately 33 subjects in each of three driver age groups were studied: ages 2040, ages 6569, and age 70 and older. A guide written for the California Department of Transportation by Ourston and Doctors (1995) is based on British standards; according to Jacquemart (1998), Caltrans decided not to publish it. FHWA's Every Day Counts 2 initiative has listed "Intersections with Displaced Left-turns or Variations on U-turns" among the treatments for Intersection and Interchange Geometrics that state departments of transportation should consider to reduce conflicts and improve safety. This understanding of the downstream intersection geometry is accomplished by the driver's visual search and successful detection, recognition, and comprehension of pavement markings (including stripes, symbols, and word markings); regulatory and/or advisory signs mounted overhead, in the median, and/or on the shoulder in advance of the intersection; and other geometric feature cues such as curb and pavement edge lines, pavement width transitions, and surface texture differences connoting shoulder or median areas. This time is equivalent to ta in the 1994 AASHTO model, as shown in Figure IX-33 in the AASHTO (1994)Green Book. As discussed underDesign Element 4, subsequent analyses established a recommendation for use of an 8.0-s gap size (plus 0.5 s for each additional lane crossed) to adjust the Gap Acceptance to accommodate aging driver needs for increased sight distance. Based on their study findings, the authors recommend protective phasing for use at high-speed intersections (e.g., those 45 mph or higher). The restriction of sight distance for an unpositioned versus a positioned driver at an intersection with aligned left-turn lanes is shown inFigure 76.

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