On the basis of day-night crash distributions, this translates into a 4 percent reduction in total crashes at an intersection where lighting is added and a 5 percent reduction in all injury crashes. In most advanced APS devices, these special features are actuated by pressing and holding the pedestrian pushbutton for an additional length of time (Noyce and Bentzen 2005). Using these results, most standards set requirements for green and yellow to be 1.3 and 3.0 times that of red, respectively. Among the many additional findings with regard to walking speed were the following: For design purposes, a separate analysis was conducted by Knoblauch, et al. The majority of the 65 "like" comments pertained specifically to smoother and better traffic movement. During a fourth circuit, they were asked to brake to a stop, if they possibly could, if the light changed from green to yellow. 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. 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). In a survey of aging drivers conducted by Yee (1985), 35 percent of the respondents reported problems with arthritis and 21 percent indicated difficulty in turning their heads to scan rearward while driving. 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). First, driver age differences in cognitive and physical capabilities that are relevant to ISD issues will be discussed. The border on street name signs is presumed to enhance the conspicuity of the sign panel at intersections, where visual complexity and driving task demands may be relatively high. If they are waiting at a right-hand curb, they will often take time to glance to their left rear to see if an entering vehicle is about to make a right turn across their path. Drivers were shown photographs of left turn displays from various signalized intersections around the country. Burnham (1992) noted that the selection of letter size for any sign must evaluate the needs of the user, which are continuously changing as a function of changes in automotive technology, the roadway system, and the population itself. Carstens and Woo (1982) found that primary highway intersections where rumble strips were installed experienced a statistically significant reduction in the crash rate in the first year or two following their installation, both at four-way and T-intersections. It was therefore recommended that the supplemental message WHEN PEDESTRIANS ARE PRESENT be added to theMUTCDas an accepted message that may be used with an NTOR sign when right-turn volume is light to moderate and pedestrian volumes are light or occur primarily during intermittent periods, such as in school zones. The three age groups were "young/middle-aged" (ages 2545), which contained 32 drivers; "young-old" (ages 6574), containing 36 drivers; and "old-old" (age 75 and older), containing 32 drivers. The remaining participants said that these distances should be increased. Harwood et al. A great deal of existing research on roundabouts has not been conducted specifically from the perspective of the aging road user, but the benefits apply to drivers and pedestrians of any age. Looking at the effects of font on legibility distance, there was no significant difference in the daytime legibility distances obtained with the Series E(M) font and the Clear 100 and Clear 112 fonts. Poor comprehension that entry from either lane was allowable could interfere with roundabout capacity design calculations. Garvey, Pietrucha, and Meeker (1997) investigated an experimental font in two controlled field studies, using drivers ages 65 to 83. They recommended that this sign be added to theMUTCDas an option for use at locations with a high number of pedestrian crashes involving turning vehicles. When you approach an intersection with a "STOP" sign, you must come to a complete stop and yield to pedestrians crossing the street and cross-traffic. 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. Apparently reinforcing this notion, the Maryland State Highway Administration (MSHA, 1993) reported a higher rate of left-turn collisions at three intersections where the R10-12 sign was installed than at three intersections where the sign was not installed. Jacquemart (1998) reports findings by Niederhauser, Collins, and Myers (1997) who showed that the average cost per crash decreased by 30 percent across the 5 conventional intersections in Maryland that were retrofitted to roundabouts, from $120,000 before the roundabout to $84,000 after the roundabout. Description of Practice:Within the last five years, interest in a set of intersection designs collectively called "innovative" or "alternative" has grown rapidly. Most commonly, this is used in the vicinity of the curb ramp to enable the WALK signal to be requested without the pedestrian needing to use a pushbutton. Roundabout Sign Recommended by Lord et al. Kyte (1995) recommended a critical gap value of 4.2 s for left turns from the major road by passenger cars for inclusion in the unsignalized intersection analysis procedures presented in theHighway Capacity Manual(Transportation Research Board, 1994). The lower ratings during daylight conditions could be due to sun glare or shadow issues mentioned by the participants. Studies in other countries help to shed some light on the optimum design characteristics of modern roundabouts. Before making such a move, be sure you can do so safely. The difficulty in judging gaps may lead to aborted attempts to enter the roadway, leaving the aging driver vulnerable to following drivers who direct their attention upstream and fail to notice that a vehicle has stopped in front of them. They conducted three separate on-road studies to measure driver perception-brake response time to several stopping sight distance situations. What Are the Rules When Facing a STOP Sign? Modern roundabouts are an intersection design that has been in use in Europe and Australia for decades, but have more recently come into their own in the United States. In particular, it is important to rule out the possibility that the FYA will be (mis)perceived as the timing out of a protected left turn phase, which could actually increase the potential for injurious angle crashes. (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. Of those violations, about 23.4 percent resulted in conflicts with pedestrians or vehicles on the side street. 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). Figure 89. Description of Practice:Another APS treatment is passive detection. The comparison unimproved intersection included aligned left-turn lanes, which resulted in restricted sight distance. The idea is to mitigate potential accidents in uncontrolled or less controlled areas. ISD for two-way flashing operations should be determined by Case B guidance. About 20 percent of the aging drivers mentioned not stopping properly at STOP signs. McGee and Blankenship (1989) reported that intersections converted from stop to yield control are likely to experience an increase in crashes, especially at higher traffic volumes, at the rate of one additional crash every 2 years. (1998) concluded that AASHTO's 2.5-s perception-brake reaction time value is appropriate for highway design, when stopping sight distance is the relevant control. Thus, wider (12-ft) lanes used to accommodate (right) turning trucks also are expected to benefit (left) turning drivers. For each design element, a base condition (representing existing standards of engineering and design practice as per the 2003MUTCD) was presented along with two countermeasures. For older drivers as well as middle-aged drivers, crash rates were highest at the intersections with protected/permissive phasing, followed by permissive phasing. Each sign contained three place names, each containing six letters (from the same font). Analysis of police crash reports in four States indicated that drivers who are stopped at a red light are looking left for a gap in traffic and do not see pedestrians and bicyclists coming from their right (Preusser, Leaf, DeBartolo, and Levy, 1982). There was a significant difference between the partial negative offset geometry and the partial positive offset or aligned geometries, suggesting a need for longer sight distance when opposite left-turn lanes are even partially negatively offset. Regarding entry widths, 59 percent of the reported cases have single-lane entries, 30 percent have two-lane entries, and 11 percent have three or more lane entry legs. As excerpted from NCHRP Report 383, the diagram shown inFigure 71effectively illustrates how different driver decisions during a (minor) road approach to an intersection (with a major road) depend upon the planned action. This, in turn, results in a decrease in the likelihood of right-angle and other crashes (and associated injuries) that are particularly common among aging drivers making unprotected left turns. Later research (Agent, 1988) recommended the following operational improvements at intersections controlled by STOP signs: (1) installing additional advance warning signs; (2) modifying warning signs to provide additional notice; (3) adding stop lines to inform motorists of the proper location to stop, to obtain the maximum available sight distance; (4) installing rumble strips, transverse stripes, or post delineators on the stop approach to warn drivers that they would be required to stop; and (5) installing beacons. Subjects ranged in age from 18 to 80 and older, and included 64 individuals with normal color vision and 51 subjects who were color-vision deficient. ISD for a vehicle making a left-turn across the lanes used by opposing traffic. Poisson regression was used to model the relationship between left-turn crash rates with age group, type of phasing (protected, permissive, and protected/permissive), and other site characteristics including opposing volume. Thus, a general conclusion from this study is that overhead signing posted in advance of, as well as at, an intersection provides the most useful information to drivers about movement regulations which may be difficult to obtain from pavement marking arrows when traffic density is high or when pavement markings are obscured by snow or become faded, or where sight distance is limited. Staplin, et al. These analysis outcomes are reviewed below. Also, higher surround luminance improved the legibility of signs more for aging drivers and reduced the negative effects of excessive contrast. For aging pedestrians, the longer exposure time within the intersection becomes a major concern. In addition, there are many drivers who run the amber and red signals, and it is prudent for pedestrians to "double-check" that traffic has indeed obeyed the traffic signal, and that there are no vehicles turning right on red or (permissive) left on green before proceeding into the crosswalk. For the permissive indications across all age groups, the circular green ball had the fewest correct responses at 50.4%, followed by the flashing red arrow (55.6% correct) and the flashing yellow arrow (56.6% correct). Answer: Yielding the right of way is the custom and practice of letting another motorist, bicycle rider, or pedestrian enter an intersection until it is safe for you to merge into traffic. The simulator scenario was programmed so that gap acceptance at the unimproved intersection was tested as follows: drivers experienced oncoming traffic with one relatively short gap followed by more traffic and eventually a long gap without any oncoming traffic. Although other research has concluded that the left-turn arrow is more effective than the circular red in some left-turn situations in particular jurisdictions where special turn signals and exclusive turn lanes are provided (Noel, Gerbig, and Lakew, 1982), drivers of all ages will be better served if signal indications are consistent. When asked whether a supplemental sign was needed at all two-way, stop-controlled intersections to tell drivers who has the right-of-way (a diagram was provided with the question), 44 percent of the drivers responded "yes," 50 percent "no," and 6 percent "not sure." Testing was conducted using a controlled field test facility, where subjects drove their own vehicles. However, this effect is more than offset by increasing light scatter within the eye, which diminishes contrast. This Committee also conducted a survey of 111 citizens working or living near the roundabout one year after its opening to measure public opinion. (1990) concluded that for standard highway signing, an increase in character size in the range of 30 percent appears necessary to accommodate age-related acuity differences across the driving population. However, Fisher (1969) also suggested that no increase in signal intensity is likely to compensate for increasing reaction time with age. (Harkey et al., 2008) These results are based on a meta-analysis of 38 studies, including 14 conducted in the U.S. (Elvik and Vaa, 2004) and review by an expert panel as part of the referenced NCHRP study. The problems are somewhat moderated when right turns are initiated from a stop, because the turn can be made more slowly, which reduces difficulties with short radii. TheIntersection Channelization Design Guide(Neuman, 1985) states that intersections on high-speed roadways with smooth alignment should be designed with sufficient radii to accommodate moderate- to high-speed turns. MEANING: Decrease speed as you reach the intersection. 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). B1: Left Turn from the Minor Road. This study evaluated the effect of providing advance left-turn information to drivers who must decide whether or not they have the right-of-way to proceed with a protected turn at an intersection. As diagrammed inFigure 70, the four right-turn lane geometries were: Figure 70. (It should be noted that theMUTCD(2009) includes text in section 2A.07 that states that regulatory, warning, and guide signs shall be retroreflective or illuminated to show the same shape and color by both day and night, unless specifically stated otherwise in theMUTCDtext discussion of a particular sign or group of signs. This time is equivalent to ta in the 1994 AASHTO model, as shown in Figure IX-33 in the AASHTO (1994)Green Book. 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. The results of the appearance ratings of the markings on a scale of A to F mirrored the findings from the detection distance evaluation. It may be remembered that aging pedestrians stand farther away from the curb, and may or may not be alert. A variety of conspicuity-enhancing treatments are mandated in current practice. A study of pedestrian crashes conducted at 31 high-pedestrian crash sections in Maryland between 1974 and 1976 showed that pedestrians age 60 and older were involved in 53 (9.6 percent) of the crashes, and children younger than age 12 showed the same proportions. The range for red signals among all of these standards is from 157 cd (TEH) to 475 cd (British Standards Organization). Data from 124,000 two-vehicle crashes (54,000 crashes at signalized intersections and 70,000 crashes at unsignalized intersections) showed that drivers younger than age 25 and older than age 65 were overinvolved in crashes at both types of intersections (Stamatiadis et al. The "left-turn trap" occurs when the left-turning driver's right-of-way is terminated, while the opposing (oncoming) approach continues with a green arrow and an adjacent through movement. The sample included 101 intersections with at least one intersecting roadway with a speed limit of 45 mph or higher. The use of a ONE WAY sign on the center island was associated with increased ratings over the baseline (no signs); there were no significant differences between the countermeasures, however, comments provided by study participants indicated placement to maximize the visibility of a driver just about to enter the roundabout is beneficial. Comprehension for "either" lane entry options was only 44 percent, and was not significantly different across the 5 schemes. Recommended Wording For Educational Placards For One-Stage And Two-Stage Crossings (Knoblauch et al., 1995). 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. The authors concluded that the guidelines for extended receiving lane width at intersections are effective for driver safety, and improve the performance of older as well as younger drivers. Avoid entries and exits with two or more lanes, except for capacity requirements. Of course, a conflict must be seen before any cognitive processing of this sort proceeds. The microprismatic sheeting showed the same trend (although not significant), with the Clear 112 font producing 11 percent longer legibility distances than the Series E(M). 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.) on Curb Radius, Paras. Figure 77. (2) designate an intersection on a highway under its jurisdiction as a stop intersection or a yield intersection and place a sign at one or more entrances to the intersection. This approach, incorporating the parameters represented in the intersection diagram shown earlier inFigure 72(seeDesign Element 4 Intersection Sight Distance), was applied to the intersections in the study by Staplin et al. Right of Way at Intersections: Who Goes First and When to Yield The perceptual task of turning left from a major roadway at an unsignalized intersection or during a permissive signal phase at a signalized intersection requires a driver to make time-distance estimates of a longitudinally moving target as opposed to a laterally moving target. Participants "drove" through double-lane roundabouts marked with five signing and pavement marking schemes: A sixth condition with no lane restriction signs or markings, served as the control. A driver's response to intersection geometric features is influenced in part by the processing of high-spatial-frequency cuesfor example, the characters on upstream advisory signsbut it is the larger, often diffuse edges defining lane and pavement boundaries, curb lines, and raised median barriers that are the targets with the highest priority of detection for safety. In a survey of aging pedestrians in the Orlando, Florida area, 25 percent of the participants reported difficulty seeing the crosswalk signal from the opposite side of the street (Bailey, et al., 1992). However, there is some inconsistency among reference sources concerning the degree of skew that can be safely designed into an intersection. Measures of effectiveness included percent of correct responses to the study scenarios and response time. The yield sign is one of these. Although the cognitive aspects of safe intersection negotiation depend upon a host of specific functional capabilities, the net result is response slowing. Mixed-case font, on the other hand, produces words with a recognizable overall shape, due to the ascending and descending elements in each letter. For example, a corner radius of 50 ft will accommodate moderate-speed turns for all vehicles up to WB-50 (combination truck/large semitrailer with an overall length of 55 ft). (1965) and Jainski and Schmidt-Clausen (1967). 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. Jacquemart (1998) reports that as of the middle of 1997, there were fewer than 50 modern roundabouts in the U.S., compared to more than 35,000 in the rest of the world, with France owning the leading number of roundabouts (15,000 modern roundabouts currently, and growing at a rate of 1,000 per year). The 50th percentile gap acceptance point was about 7 s (i.e., if a gap is 7 s long, only about half of the subjects would accept it). The most frequent factor was "fast moving traffic on my rear bumper," by 24 percent of the respondents, followed by "road sign name that is too small to read" by just over 20 percent of the participants. Countermeasure 2 (Yield sign with supplemental plaque "To Traffic in Circle") received significantly higher comfort ratings than the baseline condition. The U.S. (TEH) standard provides different recommendations for each of the three colors for each signal size. The lower percentage of nighttime crashes of aging drivers may be due to a number of factors, including reduced exposureaging drivers as a group drive less at nightand a self-regulation process whereby those who do drive at night are the most fit and capable to perform all functional requirements of the driving task (National Highway Traffic Safety Administration, 1987). These results suggest that at visually complex intersections with exaggerated demands for divided attention, the use of retroreflective sheeting that provides increased legibility distance would be of clear benefit to aging drivers. A constant value was recommended regardless of the number of lanes to be crossed; however, a heavy-vehicle adjustment of 1.0 s for two-lane highways and 2.0 s for multilane highways was recommended. Fambro, et al. Maximum lateral acceleration approached significance with greater values for the unimproved intersection (indicating poorer lateral control during the turn). This is because the traffic density is lighter, there are more available gaps, and there are fewer potential conflicts with other vehicles and pedestrians the farther away from the intersection the maneuver is performed. The early detection of lane control devices, by cueing the driver in advance that designated lanes exist for turning and through maneuvers, promotes safer and more confident performance of any required lane changes. 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 modal value of 200 cd, specified by Australia, South Africa, and the CIE, is based upon a depreciation factor of 33 percent. For each conversion, four years of before-crash data and four years of after-crash data were used, where available. However, a relative insensitivity to approach (conflict) vehicle speed was shown for older versus younger drivers, in that younger drivers adjusted their gap judgment of the "last safe moment" to proceed with a turn appropriately to take higher approach speeds into account, while older drivers as a group failed to allow a larger gap for a vehicle approaching at 60 mph than for one approaching at 30 mph. Sleight (1972) determined that there would be safety justification for use of walking speeds between 3.0 to 3.25 ft/s, based on the results of a study by Sjostedt (1967). Regarding public opinion about roundabout implementation, Taekratok (1998) indicates that people do not make a clear distinction between modern roundabouts and traffic circles, and therefore public responses to roundabout proposals are negative. The speed limit was 35 mph and all intersections were located on major or minor arterials within a growing urban area. The type of markings used to define a crosswalk can also make a difference in driver compliance. The use of advance street name plaques on advance warning signs has been successful in Phoenix, AZ (Rural and Urban Roads, 1973); the size of the lettering on these signs is 8 in (200 mm). For all the analyses, comparisons were made between a "young-old" group (ages 6574), an "old-old" group (age 75 or older), and a "middle-aged" comparison group (ages 3050). In this same study, it was found that the likelihood of a driver making an RTOR maneuver is reduced by intersection skew angles that make it more difficult for the driver to view conflicting traffic. Parsonson (1992) reported that the State of Delaware has found that pedestrians do not react well to the short WALK and long flashing DON'T WALK timing pattern. Shape: downward-pointing triangle Yield signs are shaped like triangles pointing downward Location: at intersections Usually posted at intersections where two roadways merge Color: always red and white Some research has indicated that the dimming of signals at night may have advantages, while also reducing power consumption. In this study, 100 subjects divided across three age groups were observed as they drove their own vehicles around test routes using the local street network in Arlington, Virginia. As noted by Lord et al., (2007) the findings from the laboratory study should be confirmed through naturalistic field study observations prior to their adoption in Federal and State design manuals. The central island can be raised or flush, or it can be raised with a sloping curb or drivable apron surrounding it. 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. Job, et al. 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 result is the need to share attention between oncoming vehicles approaching from the left and pedestrians in the path to the right. Jacquemart (1998) examined the before and after crash data of 11 roundabouts in the U.S. 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. For the younger drivers, crash rates were highest with permissive phasing, followed by protected/permissive phasing.

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