Aside from (conflict vehicle) motion detection, an additional concern is whether there are age differences in how well drivers understand the rules under which the turns will be madethat is, whether aging drivers have disproportionately greater difficulty in understanding the message that is being conveyed by the signal and any ancillary (regulatory) signs. The Clear 112 and Clear Condensed 112 fonts produced significantly longer recognition distances than the all-uppercase Series D font. photo illustrates how overhead structures can affect sight lines. Figure 23. At the same time, there are significant human factors concerns about special driving task demands associated with the geometric and operational characteristics of roundabouts, and their novelty in this country. However, when comparing the Clear Condensed 100 and Clear Condensed 112 to the Series D font, the mixed-case fonts produced significantly longer recognition distances (14 percent greater) than the all uppercase Standard Highway font. All subjects had a visual acuity of at least 20/40. For the word legibility study, subjects were presented with only one word on a sign, and were required to read the word. Proper allocation of attention has become more difficult, as drivers are overloaded with more traffic, more signs, and more complex roadway configurations and traffic patterns, as well as more complex displays and controls in newer vehicles (Dewar, 1992). (1995) reported that, compared with younger pedestrians, aging adults are overinvolved in crashes while crossing streets at intersections. Harwood et al. One particular technology is that in which a controller can be programmed to provide extended pedestrian phase timing in response to an extended button press. B2: Right Turn from the Minor Road. The ability to read street signs is dependent on visual acuity as well as divided attention capabilities, both of which decline significantly with advancing age. Pedestrian trappedAt a signalized intersection, a pedestrian is hit when a traffic signal turns red (for the pedestrian) and cross-traffic vehicles start moving. The study population excludes persons in nursing homes or hospitals. All intersections were controlled by traffic signals with yield control on the three channelized intersections. The four options were: (1) GO, (2) YIELD and wait for gap, (3) STOP then wait for gap, and (4) STOP. Upon closer approach, the appropriate speed and heading changes to conform to the splitter island's controlling channelization must be performed; and where increased crash experience has been documented following roundabout installation, as discussed below, excessive entry speeds have been the prevalent contributing factor. In this study, 14 drivers ages 19 to 57 (median age = 40 years) viewed signs with fluorescent red sheeting and signs with standard red sheeting at a distance of 98 ft. Crosswalk detectors can be infrared or microwave detectors mounted on the signal pole or video cameras serving remote sensor software. The typical curbed median offers low to no contrast with the adjacent pavement and is difficult to reflectorize at night. Also, older persons participating in laboratory studies have been observed to require significantly longer intervals than younger persons to perceive that a vehicle was moving closer at constant speed: at 19 mph, decision times increased 0.5 s between ages 20 and 75 (Hills, 1975). The Clearview font was produced in a regular version, with visual proportions similar to the Standard FHWA Series E(M) font, as well as in a condensed version, with visual proportions similar to the Standard FHWA Series D font. Regarding the response times to the signals in the Noyce and Kacir (2002) study, the average response increased with driver age. Official websites use .govA .gov website belongs to an official government organization in the United States. 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. 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. Of those who responded incorrectly, 13.6 percent responded that they would wait for the green arrow, and 4.3 percent made the dangerous interpretation that the left turn was protected when the circular green was illuminated. 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. Intersections with changing traffic patterns. However, while accurate perception of the distance to geometric features delineated at intersectionsas well as to potentially hazardous objects such as islands and other raised featuresis important for the safe use of these facilities, relatively greater attention by researchers has been placed upon motion perception, where dynamic stimuli (usually other vehicles) are the primary targets of interest. Absolute minimum widths of 9 ft should be used only in unusual circumstances, and only on low-speed streets with minor truck volumes." PDO crashes increased at a roundabout in Vail, CO from 15 to 18 per year, and at Leeds, MD from 1.5 to 5.3 per year. This study compared the decision/response times and deceleration characteristics of older drivers (ages 6071 and older) with those of younger drivers (younger than age 60) at the onset of the amber signal phase. It is important to note that the NCHRP study did not consider driver age as a variable. 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. During the LPI condition, 860 seniors and 4,288 nonseniors were observed. The range for red signals among all of these standards is from 157 cd (TEH) to 475 cd (British Standards Organization). The PRT is defined as the time from the driver's first look for possible oncoming traffic to the instant the car begins to move. Stopping Sight Distance (SSD) is the viewable distance required for a driver to see so that he or she can make a complete stop in the event of an unforeseen hazard. stopping sight distance during daylight conditions, but very short sag 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. (1992), reported that intersections with too many islands are confusing because it is hard to find which island the driver is supposed to go around. The IHSDM (see Chapter 1) creates stopping sight distance profiles for rural two-lane highways. Not all locations with limited stopping sight distance are the same in terms of safety risk. In this example, the intersecting roadway in the background creates the illusion of a straight alignment and may increase the risk of run-off-road crashes. The supplemental message when added to the NTOR sign with the circular red symbol reduced total pedestrian conflicts at one site and increased RTOR usage (as desired, from 5.7 percent to 17.4 percent), compared with full-RTOR prohibitions. Before-and-after studies where intersections were changed from protected to permissive control have shown four- to seven-fold increases in left-turn crashes (Florida Section of Institute of Transportation Engineers, 1982; Agent, 1987). Longitudinal movement is a greater problem for drivers because the same displacement of a vehicle has a smaller visual effect than when it moves laterallythat is, lateral movement results in a much higher degree of relative motion (Hills, 1980). Reductions in visual acuity make it more difficult for aging pedestrians to read the crossing signal. An example of passive pedestrian detection technology is the "Pedestrian User-Friendly Intelligent" (PUFFIN) crossing in use in England (Department of Transport, 2006). 160 Exhibit 6-31. In these tables, it is recommended that the existing treatment remain in place when the benefit-cost ratio (in terms of delay and safety) is less than 1.0, and when the benefit-cost ratio exceeds 2.0, it is recommended that the engineer consider adding the alternative treatment. (2007) recommended the use of the roundabout advance warning sign, augmented with a symbol representing the center island, as shown inFigure 82. This study was conducted to evaluate countermeasures to address the over-representation of pedestrians age 70 and older in crashes in the greater Sydney metropolitan area. There were no differences in the other kinematic measures when comparing the two age groups. (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. Policy on Design Standards Interstate System, A For SSD, this is the time from object or hazard detection to initiation of the braking maneuver. 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. (1987) concluded that aging drivers may be particularly disadvantaged when they are required to initiate a movement in which there is no opportunity to prepare a response. This obviously takes time, especially for those drivers with lower levels of physical dexterity, e.g., aging drivers. (1986) examined the PRT of 124 subjects traversing a 3-hour test circuit which contained scenarios identified above as Cases II, IIIA, IIIB, and IIIC. Approach sight distance. (1996) recommended a critical gap for left turns from the major roadway of 5.5 s, and an increase in the critical gap to 6.5 s for left turns by single-unit trucks and to 7.5 s for left turns by combination trucks. They conducted three separate on-road studies to measure driver perception-brake response time to several stopping sight distance situations. Figure 89. However, for the higher-speed approach (55 mph), the minimum gaps accepted by the older drivers (females = 7.11 s; males = 6.23 s) were not significantly larger than the younger drivers (females = 6.0 s; males = 5.26 s). Data describing the safety impact of RTOR were provided by Compton and Milton (1994) in a report to Congress by the National Highway Traffic Safety Administration. Data for yield-controlled intersections showed older drivers over-contributing to left-turn collisions in urban areas and to angle collisions in both urban and rural areas. Absolute minimum widths of 9 ft should be used only in unusual circumstances, and only on low-speed streets with minor truck volumes.". An inventory of the materials and devices commonly employed to delineate roadway edges, curbs, medians, and obstacles includes: retroreflective paint or tape, raised pavement markers (RPM's), post-mounted delineators (PMD's), object markers, and chevron signs. (1995) for one-stage and two-stage crossings is shown inFigure 80. vertical curves to satisfy the comfort criteria over the typical design Vehicle turn/mergeThe vehicle turns left or right and strikes the pedestrian. The tunnel wall at right obscures the view ahead sight distance profile allows a designer to identify the region of minimum In a retrospective site-based review and crash analysis that included a detailed investigation of over 400 crashes involving drivers age 65 years and older at 62 sites in Australia, limited or restricted sight distance at right turns (equivalent to left turns in the U.S.) contributed to 23 percent of the crashes, and restricted sight distance plus a lack of right-turn offsets (i.e., left-turn offsets in the U.S.) contributed to an additional 10 percent of the crashes (Oxley, et al., 2006). 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. One factor is the diminishing ability to share attention (i.e., to assimilate and concurrently process multiple sources of information from the driving environment). of the hill. The diversion of attention, along with movement of the upper torso, hampers the aging driver's ability to maintain directional control. FHWA released two Roundabout Guides (Robinson, et al. Poor comprehension that entry from either lane was allowable could interfere with roundabout capacity design calculations. To determine what adjustment is most appropriate in this regard, a set of analyses were performed in which the goal was to identify a value of G that would yield required sight distance values meeting or exceeding those derived from the modified AASHTO model formula (i.e., where J = 2.5 s). However, the fact that in 11 percent of the scenarios, drivers continued to make left turns from the right lane, even when the signs and markings clearly showed that the right lane must turn right is both an operational and safety concern.