Aging persons may in fact require twice the rate of movement to perceive that an object is approaching, versus maintaining a constant separation or receding, given a brief duration (2.0 s) of exposure. Skewed intersections pose particular problems for aging drivers. Sight distance criteria are provided for the following types of intersection controls: Left turns from the major road. Sight distance through a grade crossing should be at least the minimum stopping sight distance, or longer. Line of sight may be obstructed by an overpass structure and can limit the sight distance for the operator. Detectability of a pedestrian is generally influenced by contrast, motion, color, and size (Robertson, Berger, and Pain, 1977). Figure 81. Section 2D.03 further states that all messages, borders, and legends on guide signs shall be retroreflective, and all backgrounds shall be retroreflective or illuminated.) less. This feature is particularly useful where site constraints make it difficult for pedestrians with disabilities to approach the pushbutton. In addition to intersections converted from four-way to two-way stop control, these include: The intersection of two single-jurisdictional roadways (e.g., two state-maintained roadways) in a rural or isolated area. Multiple threatOne or more vehicles stop in the through lane, usually at a crosswalk at an unsignalized intersection. Understanding these roundabout operational rules is paramount to avoiding wrong-way maneuvers (and their consequent head-on crashes), panic stops by circulating traffic trying to avoid crashing into a driver who does not yield at entry (resulting in rear-end crashes by following circulating drivers), and angle crashes between entering and circulating drivers when an entering driver fails to yield and an approaching driver does not take evasive action. If the radii are too large, pedestrian exposure may be increased (although, if large enough, refuge islands may be provided). These levels include: (a) 6-ft "partial positive" offset, (b) aligned (no offset) left-turn lanes, (c) 3-ft "partial negative" offset, and (d) 14-ft "full negative" offset. Joshua and Saka (1992) noted that sight distance problems at intersections which result from queued vehicles in opposite left-turn lanes pose safety and capacity deficiencies, particularly for unprotected (permissive) left-turn movements. The FYA research noted above targets apparent deficits in the comprehension of the conventional green ball for permissive turning operations at intersections, which has been discussed elsewhere in this section. AASHTO values (for both uncontrolled and stop-controlled intersections) for available sight distance are measured from the driver's eye height (currently 3.5 ft above the roadway surface) to the object to be seen (currently 3.5 ft above the surface of the intersecting road). The 200-cd requirement for red signals, as noted earlier, must be met after the depreciation factor has been taken into account. Because intersections define locations with the highest probability of conflict between vehicles, adequate sight distance is particularly important. The subjects included nine males ages 68 to 74, and nine females ages 62 to 83. C2: Left or Right Turn from the Minor Road. Present recommendations for applications of fluorescent sheeting are limited to the special cases of controlling prohibited movements on freeway ramps (seeChapter 3) and for passive control systems at highway-rail grade crossings (seeChapter 6). With regard to the effect of driver age on legibility, Olson, Sivak, and Egan (1983) concluded that older drivers require more contrast between the message and the sign's background than younger drivers to achieve the same level of comprehension. The author used these data to dispel the findings in the literature that aging pedestrians are not cognizant of the risks of exposure to injury from passing vehicles. (1992) examined the issue of offset left-turn lanes, and developed an approach that could be used to compute the amount of offset that is required to minimize or eliminate the sight restriction caused by opposing left-turn vehicles. Thus, for a sidewalk whose centerline is 6 ft from the roadway edge, a 15-ft corner radius increases the crossing distance by only 3 ft. They noted that on rural roads, lanes wider than 12 ft or 13 ft allowed oncoming vehicles on the cross street to move further right to avoid trucks, and shoulders wider than 4 ft allowed oncoming vehicles a greater margin of safety. Greene, et al. This countermeasure, it has been suggested, addresses problems that aging drivers experience in judging speeds and gaps, understanding operational rules at complex intersections, and maneuvering through turns. Female drivers age 75 and older always stopped before a RTOR. The sample contained 88 drivers age 65 and older. The mean crossing speed for the young compliers was 4.79 ft/s and for the older compliers was 3.94 ft/s. These differences were statistically significant. The splitter island is the geometric feature that physically separates entering traffic from exiting traffic, and defines the entry angle, which deflects and slows entering traffic. They concluded that driver performance measured by the probability of exceeding lane limitswas optimized when the perceived brightness contrast between pavement markings and the roadway was 2.0. A 40 ft/in standard can generally be effective for aging drivers, given contrast ratios greater than 5:1 (slightly higher for guide signs) and luminance greater than 10 cd/m2for partially reflectorized signs. In particular, the most problematic displays were those with only one steady illuminated signal face (circular green) accompanied by a sign that indicated that it was not safe to proceed into the intersection with the assumption of right-of-way (LEFT TURN YIELD ON GREEN). In this study, average adults and the elderly had walking speeds of 4.5 ft/s; however, 20 percent of the aging pedestrians crossed at speeds slower than 4.0 ft/s. Then, research efforts that have attempted to quantify the safety impact of providing adequate sight distance are summarized, plus studies examining the appropriate values for specific components used when calculating sight distance in the AASHTO gap acceptance models. Except for the destination lane restriction sign condition, all roundabouts had redundant indications of proper lane approach. TheMUTCDincorporates the intensity, light distribution, and chromaticity standards from the following Institute of Transportation Engineers (TEH) standards for traffic signals:Vehicle Traffic Control Signal Heads, TEH Standard No ST-008B (TEH, 1985b);Pedestrian Traffic Control Signal Indications, TEH Standard No. Eliminate holiday decorations located overhead at intersections, because they are often green and red and may be confusing near signal faces. Looking at flared approaches from the viewpoint of accommodating aging driver needs for simplicity, one-lane approaches are likely to be easier to negotiate. Drivers interpreted the Delaware signal as requiring a full stop before turning, because a red indication usually means 'stop," even though the signal is meant to remind motorists to exercise caution but not necessarily to stop unless opposing through traffic is present. Thus, when ISD is calculated using the AASHTO model as it relates to drivers turning left from a major roadway, there is evidence that the PRT value should be increased to 2.5 s to provide adequate sight distance. At unsignalized intersections, aging drivers showed the highest crash frequency on major streets with two lanes in both directions (a condition most frequently associated with high-speed, low-volume rural roads), followed by roads with four lanes, and those with five lanes in both directions. A detailed description of the model parameters and output can be found in the FHWA report entitled Intersection Geometric Design and Operational Guidelines for Older Drivers and Pedestrians (Staplin et al., 1997). (SeeFigure 76, located in the discussion forDesign Element 5 Offset Left Turn Lanes, for an illustration of driver positioning within an intersection). While the number of injuries is close to the population distribution (approximately 12 percent), the number of fatalities far exceeds the proportion of aging pedestrians. The visibility of an object is that property which makes it discernible from its surroundings. The average annual frequency of total crashes was reduced at 12 of 13 study sites after implementation of the FYA indication, and the average annual frequency of left-turn crashes was reduced at all 13 study sites. Drivers approaching an unsignalized intersection must be able to detect the presence of the intersection and then detect, recognize, and respond to the intersection traffic control devices present at the intersection. Specific benefits for aging drivers are a subject worthy of further exploration, but indications are that they can improve operations and safety for aging drivers as with the driving population as a whole. (2007). The difficulty aging persons experience in making extensive and repeated head movements further increases the decision and response times of aging drivers at intersections. However, when parallel parking is not allowed, the TWLTL has about the same crash frequency as the undivided cross section at lower traffic volumes. Jainski and Schmidt-Clausen (1967) tested the ability of observers to detect the presence of a red, amber, or green spot, which was either 2 minutes or 1 degree, against varying background luminances. Although the total number of crashes was reduced at unsignalized intersections that contained signs when compared with unsigned intersections, the crash involvement ratios of aging drivers were higher at signed intersections than at unsigned intersections. Five roundabouts had a posted speed of 35 mph and one had a posted speed of 45 mph. Specifically, the following advantages of roundabouts for aging road users have been postulated: Reductions in the speed of vehicles entering the intersection/circle this makes it easier to choose an acceptable gap to merge into, removes the need to accelerate quickly which occurs after a conventional right turn, and results in lower severity crashes with less serious injuries. The duration of the yellow signal was 3.0 s before turning to red. The effect of any traffic control measure is highly dependent on specific locational characteristics, such as traffic conditions (e.g., volumes, speeds, turning movements), pedestrian volumes and pedestrian mix (e.g., young children, college students, aging adults, persons with physical disabilities), street width, existing traffic controls, area type (e.g., rural, urban, suburban), site distance, crash patterns, presence of enforcement, and numerous other factors. Description of Practice:A broad range of technologies can be classified as Accessible Pedestrian Signal (APS) treatments (Harkey, et al. 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. Comparison of Required Intersection Sight Distance Values from the Modified AASHTO Model (with J = 2.5 S) and the Gap Acceptance Model (with Gap Values of 5.5 S, 7.0, 7.5 S, and 8.0 S). The effectiveness of fixed lighting in improving the detectability of pedestrians has been reported by Pegrum (1972); Freedman, et al. Williams, Ardekani, and Asante (1992) conducted a mail survey of 894 drivers in Texas to assess motorists' understanding of left-turn signal indications and accompanying auxiliary signs. The high crash rate for protected/permissive phasing may also be a reflection of driver misunderstanding of protected/permissive signal displays. In developing the Gap Acceptance model for Case V, Harwood et al. To the extent that aging drivers experience any of these limitations, they should derive an extra benefit from advance warning messages presented as pavement markingsif these markings are applied and maintained at contrast levels sufficient to ensure legibility to an "aging design driver.". When the green-arrow and red-ball indications were shown simultaneously in the 5-section signal display, driver understanding was lowest with the horizontal arrangement. 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. A driving evaluator sat in the car and recorded behavioral errors as subjects "drove" through 8 intersections. The mean legibility distances for the signs mounted on the right side of the road and corresponding luminances of the sheeting at the legibility distances are as follows: Type VII=205 ft) and 4.392 cd/m2; Type IX=201 ft and 7.369 cd/m2; Type III=177 ft and 1.1314 cd/m2; and Type I=174 ft and 0.9671 cd/m2. The authors noted that the walking speed of aging pedestrians varies according to functional classification, gender, and intersection type, and stated that approximately 95 percent of pedestrians in this study would be accommodated using a design walking speed of 2.62 ft/s. In Case II, SSD is the design value; thus, the PRT is 2.5 s. For all Case III scenarios and Cases IV and V, the PRT is assumed to be 2.0 s. Refer toTable 14to cross-reference the 1994 vs. 2011 intersection scenarios. In this same vein, it was reported inTransportation Research Circular 382(Transportation Research Board, 1991) that the aging driver, having poorer vision, slower physical reaction time, lower degree of awareness, and reduced ability to maneuver the vehicle, is more likely to be negatively affected by a raised median than is the average driver; and, because medians are fixed objects, when they are struck they pose a serious threat of loss of control, especially for aging drivers. Thus, wider (12-ft) lanes used to accommodate (right) turning trucks also are expected to benefit (left) turning drivers. A high-speed road is defined as one with speeds up to 62 mph, distances up to 787 ft, and sky luminances up to 10,000 cd/m2. Burnham (1992) noted that signs located over the highway are more likely to be seen before those located on either side of the highway. This countermeasure resulted in an overall reduction in RTOR violations and pedestrian conflicts. The average response time for the 5-section signal displays showing green-arrow and green-ball indications simultaneously was not different from that for the 3- and 4-section displays showing the green-arrow only indication. There were no differences in maximum speed between the improved and unimproved intersection. The signs with fluorescent red sheeting were detected by 90 percent of the participants; only 23 percent were able to detect the standard red signs. Physically separating the target stimulus from potentially distracting stimuli in the roadside environment should result in faster and more reliable visual detection, and this performance advantage for an overhead signal (especially with a backplate) compared to a pedestal mount should be disproportionately greater for aging drivers with a reduced ability to 'screen out" irrelevant stimuli (selective attention). WebFigure 1: Parameters used to determine length of vertical curve. Drivers in the 70 and older age group showed difficulty at two of the STOP signs on the test route; their errors were in failing to make complete stops, poor vehicle positioning at STOP signs, and jerky and abrupt stops. Garber and Srinivasan (1991) conducted a study of 2,550 crashes involving pedestrians that occurred in the rural and urban areas of Virginia to identify intersection geometric characteristics and intersection traffic control devices that were predominant in crashes involving aging pedestrians. Males had higher percentages of correct responses for both compliance and comprehension than females; however, the difference was significant only for compliance. 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. (1997) performed a laboratory study, field study, and sight distance analysis to measure driver age differences in performance under varying traffic and operating conditions, as a function of varying degrees of offset of opposite left-turn lanes at suburban arterial intersections. The authors further concluded that "although the 53% reduction in collisions overstates the impact of the countdown, a real reduction did occur.". At suburban intersections, it is therefore suggested that the median should not generally be wider than necessary to accommodate pedestrians and the appropriate median left-turn treatment needed to serve current and anticipated future traffic volumes. Young/middle-aged drivers made an RTOR without a complete stop nearly 35 percent of the time, compared with nearly 25 percent for the young-old and 3 percent for the old-old drivers. While 66.5 percent of crashes involving drivers ages 3650 occurred at intersections, the percentage increased to 69.2 percent, 70.7 percent, and 76.0 percent for drivers ages 5564, 6574, and 75 and older, respectively. Slightly less than one-half of these crashes involved a pedestrian (44 percent), 10 percent involved a bicyclist, and 33 percent involved one vehicle striking another. Several data elements collected in the field received special attention. More specifically, Curtis et al. Critical gap data were not collected in this study for drivers who did not position themselves within the intersection, but it is important to note that the older drivers were less likely to position themselves within the intersection than the young and middle-aged drivers. Similar concern was raised by highway engineers surveyed by Harwood et al. The narrower throat width resulted in higher encroachments by aging drivers, who physically may have more difficulties maneuvering their vehicles through smaller areas. (AASHTO 2011) When the headlamp beam distance is less than the length of the sag vertical curve, the equation from either figure 23 or figure 24 is used. Overall, findings indicated that the reaction times for all subjects were the shortest for signal designs with larger 12-in lenses and higher luminances (150-W bulbs). Crash frequency by location and age for the crashes within the cities showed that while the highest percentage of crashes involving pedestrians age 59 and younger occurred within 150 ft from the intersection stop line, the highest percentage of crashes for pedestrians age 60 years and older (51.8 percent) occurred within the intersection. It further specifies in Table 4-9 the operational characteristics for various corner radii. These analysis outcomes are reviewed below. For example, longer perception-reaction times may be appropriate for intersection or interchange design where more complex decisions and driver speed and/or path correction are required. The minimum sight distance available on the roadway should be suffi ciently long to enable a vehicle traveling at or near the design speed to stop or change lanes There was a small increase in the percentage of pedestrians who left early (i.e., on the flashing hand or solid hand) but that increase was not statistically significant. the intersecting roadway in the background creates the illusion of a straight The Each photograph was taken from approximately the driver's eye location as if the driver were positioned as the first left-turn vehicle in queue in an exclusive left-turn lane. A study investigating causes of aging driver over-involvement in turning crashes at intersections, building on the previously reported decline for detection of angular expansion cues, did not find evidence of overestimation of time-to-collision (Staplin et al., 1993). Research findings indicated that an increase in sight distance through positively offsetting left-turn lanes can be beneficial to left-turning drivers, particularly aging drivers. (1995) study showed no significant differences in 85th percentile decision/response times between younger and older drivers when subjects were close to the signal at either approach speed. After the introduction of the LPI, the number of conflicts averaged 0.1, 0.1, and 0.2 for the three sites. Similar patterns emerged from examination of the rural signalized-intersection pre-crash maneuvers, with middle-aged drivers most often traveling straight, and older drivers most often turning left or right. Even though a curve warning sign is present, a The third possibility is to cut across the apex of the turn, possibly dragging the rear wheels over the curb. Of particular interest, however, are findings reported by Burns and Pavelka (1995) for a field study conducted at dusk (15 min after sunset), without the use of vehicle headlights. (1998) found significant differences in mean perception-brake response times as a function of age and gender, with aging drivers and female drivers demonstrating longer response times. They compared older and younger driver performance at improved and unimproved intersections in a high-fidelity, virtual reality driving simulator to test the effectiveness of FHWA's recommendations for intersection design to accommodate aging road users. Retroreflectance values were calculated based on the luminance levels needed to accommodate 67, 85, and 95 percent of the population of U.S. drivers. Turning left at intersections was perceived as a complex driving task, made more difficult when channelization providing visual cues was absent and only pavement markings designated which lane ahead was a through lane and which was a turning lane. A driver who is properly positioned for a downstream maneuver will experience reduced demands for divided attention as s/he nears the intersection. Presently, several States have design guidelines for roundabouts (Florida, 1996 and Maryland, 1995) based largely on Australian guidelines. This implies that drivers show more sensitivity to oncoming vehicle distance than to oncoming vehicle approach speed. Researchers have postulated further safety gains by adding a 1-inch to 3-inch yellow retroreflective strip around the perimeter to "frame" the backplate. Aging pedestrians, who as a group walk more slowly, should benefit from the shorter crossing distances afforded by this design. About 20 percent of the aging drivers mentioned not stopping properly at STOP signs. There were 27 incapacitating injury crashes in the before period, and 3 in the after period. Stopping sight distance is influenced by both vertical and horizontal It provides an option for using 4-in upper-case lettering and 3-in lower-case lettering on street name signs that are posted on local roads with speed limits 25 mph or less. Since aging drivers benefit from longer exposure to stimuli, Winter (1985) proposed that signs should be spaced farther apart to allow drivers enough time to view information and decide what action to take. Posting the advance signing described in this treatment overhead increases the conspicuity of this guidance information; this is likely to have the greatest benefit for aging drivers who, as a group, do not execute visual search as efficiently as younger persons when concurrent task demands are high. WebA TTC plan should be designed so that vehicles can travel through the TTC zone with a speed limit reduction of no more than 10 mph. (1995): (1) reevaluate the length of pedestrian walk signals due to increasingly wider highways, (2) implement more Barnes Dance signals at major intersections, and (3) provide more YIELD TO PEDESTRIANS signs in the vicinity of heavy pedestrian traffic. While the Montpelier, VT, Keck Circle Roundabout was under construction, the Roundabout Demonstration Committee prepared educational materials that included a brochure providing safety rules for drivers and pedestrians, as well as news releases and public service announcements in response to negative public reaction during construction, and negative commentary from local morning radio personalities (Redington, 1997). A red signal or a stop sign results in a 'stop" decision; all other types of information are functionally equivalent at this stage of driver decision making, translating into a "yield" decision.
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