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. The course took approximately 1 hour to complete, and included driving through five sets of improved and unimproved intersections. Brainan (1980) used in-car observation to gain firsthand knowledge and insight into aging people's driving behavior. Intersections of three levels of complexity were used: high complexity/ high traffic activity (e.g., large intersection in downtown business area); intermediate complexity/intermediate traffic activity (e.g., small intersection area in suburban small business/apartment area); and low complexity/low traffic activity (e.g., residential area of single-family homes). Prior work by McCoy et al. This was particularly problematic at intersections controlled by stop and yield signs. (1995) study included 10 drivers ages 16 to 34; 10 drivers ages 35 to 44; 10 drivers ages 45 to 54; 10 drivers ages 55 to 64; 13 drivers ages 65 to 74; and 10 drivers age 75 or older. The safety of aging pedestriansand all pedestriansshould also be enhanced to the extent that this design compels turning drivers to enter the turn lane at a lower speed, while permitting them to direct attention to the search for conflicts with pedestrians and conflicts with traffic in separate phases of the turning maneuver. 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. New York State DOT utilizes examples similar to the 2009 MUTCD D15-1 series sign. For older drivers as well as middle-aged drivers, crash rates were highest at the intersections with protected/permissive phasing, followed by permissive phasing. The crash rate at the 21 study intersections decreased by 51 percent for total crashes and by 38 percent for ran-STOP-sign crashes. Researchers have postulated further safety gains by adding a 1-inch to 3-inch yellow retroreflective strip around the perimeter to "frame" the backplate. Presently, several States have design guidelines for roundabouts (Florida, 1996 and Maryland, 1995) based largely on Australian guidelines. In addition, a warrant for use of a cross-traffic sign applied in the State of Illinois may be reviewed in the Gattis (1996) article. The results showed a 67 percent reduction (from 39 to 13) in crashes where obstructions that inhibited sight distance were removed; this was the most effective of the implemented improvements. Collectively, the studies described above indicate a positive relationship between available ISD and a reduction in crashes, though the amount of crash reduction that can be expected by a given increase in sight distance may be expected to vary according to the maneuver scenario and existing traffic control at the intersection. The fact that pedestrians may be crossing the side street, where they enter the path of the right-turning vehicle, places a burden upon the driver to search the right-turning path ahead. Maintained values in the range of 60 to 80 percent of initial design values are cited as common practice in this publication. (2003) conducted a laboratory study using 2,465 drivers in 4 age groups: < age 24 (27%); 25-44 (44%); 45-65 (21%); and 66+ (7%). First, driver age differences in cognitive and physical capabilities that are relevant to ISD issues will be discussed. For each conversion, four years of before-crash data and four years of after-crash data were used, where available. Chu (1994) found that relative to middle-aged drivers (ages 2564), older drivers (age 65 and older) tend to drive larger automobiles and drive at slower speeds. Knoblauch, et al. Lateral movement (also referred to as tangential movement) describes a vehicle that is crossing an observer's line of sight, moving against a changing visual background where it passes in front of one fixed reference point after another. There was no gap acceptance task at the improved intersection controlled by the protected left-turn phase. 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. Vehicle maneuvering prior to the crash was a key variable for drivers over age 65, and in particular, for left turns at uncontrolled or STOP/YIELD sign-controlled intersections. 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. Since the opposing traffic is not stopping, the turning driver is faced with a potentially hazardous situation. The pedestrian steps in front of the stopped vehicle(s) and into the path of a through vehicle in the adjacent lane. The angle complicates the vision triangle for the stopped vehicle; increases the time to cross the through road; and results in a larger, more potentially confusing intersection.". (1997) found that significantly fewer drivers in the old-old driver group attempted to make an RTOR (16 percent), compared with young/middle-aged drivers (83 percent) and young-old drivers (45 percent). Entering traffic points toward the central island, which deflects vehicles to the right, thus causing low entry speeds." Two sizes of the Clearview font were displayed: Clearview 100 (fonts matched to Standard Highway font height) and Clearview 112 (fonts 112 percent of Standard Highway font letter height, but equal in overall sign size to Standard Highway font). Computed length of conflicting leg of intersection sight triangle. More information on the specific design features and traffic control devices used at these intersections can be found in FHWA's Alternative Intersections/Interchanges: Informational Report (Hughes, et al. Combinations of protected left-turn indications, permissive left-turn indications, through-movement indications, and protected/permissive left-turn signal display arrangements were shown against these background intersection scenes. Because both the STOP and YIELD signs are so extensively overlearned by drivers, their comprehension is believed to be associated with the icon, i.e., their unique shape and coloration. The majority of the 65 "like" comments pertained specifically to smoother and better traffic movement. The State of Iowa currently utilizes some examples of overhead lane use signs, though different than the D15-1 series sign found in the 2009 MUTCD. The studies were conducted on urban or suburban arterial segments, and therefore treatments can only be applied to such environments that include the following criteria: traffic volume exceeding 7,000 vehicles per day; speed limit between 30 and 50 mph); spacing of at least 350 ft between signalized intersections; direct access from abutting properties; no angle curb parking (parallel parking is acceptable); located in or near a populated area (e.g., population of 20,000 or more); no more than six through lanes (three in each direction); and arterial length of at least 0.75 mi. A contrasting set of results was obtained in a FHWA-sponsored study of traffic operations control for older drivers (Knoblauch, et al., 1995). Table 17 summarizes the potential adverse impacts to safety and operations Knoblauch, et al. 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. 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. After the introduction of the LPI, the number of conflicts averaged 0.1, 0.1, and 0.2 for the three sites. To date, studies of traffic signal performance have not typically included observer age as an independent variable. The demonstrated lack of understanding for the red right-turn arrow (Hulbert, Beers, and Fowler, 1979) and increased violations associated with this display (Owolabi and Noel, 1985) would be of particular concern for aging road users, drivers and pedestrians alike. Raised curbs that are unmarked are difficult to see, especially in terms of height and direction, and result in people running over them. Hallmark and Mueller (2004) conducted a crash analysis to evaluate the impact of different types of left-turn phasing on older and younger drivers at high-speed intersections in Iowa. For the seven urban multilane roundabouts, a 15 percent reduction in crashes of all severities was estimated. WebStopping Sight distance is the length of roadway visible to the driver. Potentially unsafe interpretations were found for red arrow displays in protected-only operations. In an early study conducted by Hoffman (1969), the installation of overhead lane-use control signs in advance of six intersections in Michigan contributed to a reduction in the total number of crashes by 44 percent in a 1-year period, and a reduction in the incidence of crashes caused by turning from the wrong lane by 58 percent. (1997) compared the recognition distances and legibility distance of words displayed in mixed-case Clearview font with those displayed in Standard Highway Series D uppercase font, and mixed-case Standard Highway Series E(M) font. Similarly, the TEH (1984) guidelines suggest a minimum lane width of 11 ft and specify 12 ft as desirable. To compensate for this, it would appear necessary to assume a longer required visibility distance, which would result in an increase in the signal intensity required. Diagram of Median U-Turn Intersection (Image Credit: Debbie Murillo, Texas A&M Transportation Institute), Figure 90. where: L = length of vertical curve in feet (meters) S = stopping sight distance in feet (meters) A = algebraic No change was recommended because the experimental design represented a worst-case scenario for visual search and detection (drivers were required to begin their search only after they had stopped at the intersection and looked inside the vehicle to perform a secondary task). One factor is the diminishing ability to share attention (i.e., to assimilate and concurrently process multiple sources of information from the driving environment). There were 27 incapacitating injury crashes in the before period, and 3 in the after period. The protected-only/leading and protected/permissive schemes are known as "leading," and the protected-only/lagging and permissive/protected are known as "lagging" schemes. He states that the best way to control driver behavior is through the use of concrete: the roundabout has a concrete circle in the center, which defines a path to control speed, and a roundabout uses concrete islands to deter wrong-way movements and to control entry speeds. Adrian (1963) used a subjective scale and threshold detection criteria in a study that tested red and green signals at different background luminances. WebStopping sight distance is the sum of two distances: (1) the distance traversed by the vehicle from the instant the driver sights an object necessitating a stop to the instant the Isler, Parsonson, and Hansson (1997) measured the maximum head rotation of 20 drivers in each of four age groups: less than age 30; ages 40 to 59; ages 60 to 69; and age 70 and older, as well as their horizontal peripheral visual field. "Barnes Dance" or 'scramble" timing is a type of exclusive timing where pedestrians may also cross diagonally in addition to crossing the street. (1995) found that both drivers younger than the age of 65 and drivers age 65 and older failed to understand that they could turn right on a circular red after stopping in the right lane. In terms of signal head location, 4 to 5 percent more drivers were able to understand the protected/permissive display when it was centered in the left-turn lane (exclusive) as opposed to having the head located over the lane line (shared). The anticipated benefit is that fewer glances will need to be directed toward the sign to determine the legend, and more effort can be devoted to vehicle control and visual search for traffic and pedestrian conflicts. One of the survey items asked participants to pick from a list the factor that presented the greatest difficulty for them in trying to find a side road when traveling on a divided highway. However, there was a small difference in the crash rate among the last three types of phasing. The type of markings used to define a crosswalk can also make a difference in driver compliance. Sixty-one percent of the drivers older than age 49 chose "no turning left" compared with 76 percent of those younger than age 49. Intersections with changing traffic patterns. 2V =1.4 7Vt+ 30 G 32.2 100 Where: = Stopping sight distance on grade (ft)V = Design speed (mph) t = Perception/reaction time (2.5 sec) Cooper (1990) utilized a database of all 1986 police-attended crashes in British Columbia, in an effort to compare the crash characteristics of aging drivers with those of their younger counterparts. A number of research efforts have been conducted to determine appropriate PRT values for use in ISD computations. A 1982 study by the Minnesota Department of Transportation found that the average walking speed of aging pedestrians was 3.0 ft/s. Right-turn crashes accounted for 18.9 percent of crashes with pedestrians ages 6574, compared with 14.2 percent for pedestrians age 75 and older. They found that many drivers, both younger and older, do not understand the protected/permissive signal phasing, and they suggested that efforts to improve motorist comprehension of left-turn signal phasing should be targeted at the entire driving population. Forbes and Holmes (1939) used the LI to describe the relative legibility of different letter styles. Analysis of the walking speeds of 3,458 pedestrians younger than age 65 and 3,665 pedestrians age 65 and older crossing at intersections showed that the mean walking speed for younger pedestrians was 4.95 ft/s and 4.11 ft/s for older pedestrians. The agency believes that it is desirable to place these crossings at least 75 ft downstream of the exit from the roundabout and possibly augment the crossing with a signal. Zegeer, Opiela, and Cynecki (1983) found that the regulatory sign YIELD TO PEDESTRIANS WHEN TURNING was effective in reducing conflicts between turning vehicles and pedestrians. (1996) analyses pertaining to ISD for Case IIIB and IIICand by extension for Case Vare of particular interest, however, in the interpretation of related findings from an aging driver field study in this area. A decade later, Eck and Winn (2002) conducted a survey of 172 individuals between the age of 50 and 91 (mean age of 73.3). The difficulties that aging drivers are likely to experience making right turns at intersections are a function of their diminishing gap-judgment abilities, reduced neck/trunk flexibility, attention-sharing deficits, slower acceleration profile, and their general reduction in understanding traffic control devices compared with younger drivers. Crosswalk striping is not used, to avoid driver confusion of crosswalk limit lines with yield lines. Shechtman 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.". limiting sight lines in three dimensions. May (1992) noted that providing sufficient time to allow motorists to make appropriate turning movements when approaching cross streets can improve safety and reduce congestion, and that consistent street signing across political jurisdictions can be helpful in this regard, as well as presenting an orderly, predictable picture of the region to tourists, business people, and residents. 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. (1995) during the conduct of NCHRP project 15-14(2). Their results found that green required 1.0 and 2.5 times that of red, and yellow required 2.5 and 3.0 times that of red, for 1 degree and 2 minutes, respectively. 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. They proposed an enlargement from 30 x 30 in to 36 x 36 in at well-traveled intersections or at intersections of small country lanes with State highways. The number of conflicts was scored for each of these intervals, defined as any situation where a driver engaged in abrupt braking or either the driver or pedestrian took sudden evasive action to avoid a collision. The increased mobility exhibited by the two younger groups of drivers at the channelized right-turn lane locations was not, however, exhibited by the drivers age 75 and older, who stopped in 19 of the 20 turns executed at the channelized locations. Five-section protected and permissive left-turn (PPLT) displays in the protected phase illuminated both the green-arrow and through movement (green-ball or red-ball) indications as required byMUTCD. Several states and municipalities have adopted this signal head placement as policy, including Iowa, Minnesota, Virginia, and the cities of Las Vegas, Nevada and Grand Rapids, Michigan routinely place signal heads centered over each lane. Strate's analysis examined 34 types of improvements made in Federal Highway Safety Program projects. photo illustrates how overhead structures can affect sight lines. Limitations in the range of visual attention, frequently referred to as "useful field of vision," further contribute to the difficulty of aging drivers in detecting the presence of pedestrians or other vehicles near the driver's path. and other roadway features with non-standard stopping sight distance. A revision of Case V to determine a minimum required sight distance value which more accurately reflects the perceptual requirements of the left-turn task may therefore be appropriate. Combinations of permissive and protected schemes included: (1) protected-only/leading, in which the protected signal is given to vehicles turning left from a particular street before the circular green is given to the through movement on the same street; (2) protected-only/lagging, in which the green arrow is given to left-turning vehicles after the through movements have been serviced; (3) protected/permissive, in which protected left turns are made in the first part of the phase and a circular green indication allows permissive turns later in the phase; and (4) protected/permissive, in which unprotected turns are allowed in the first part of the phase and protected left turns are accommodated later in the phase. However, they caution that all seven of these roundabouts were located in one State (Colorado) where three of the four in the city of Vail were part of a freeway interchange that also included nearby intersections that were previously four-way stop-controlled. 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. The concern expressed was that drivers turning left from the minor road may turn too soon and enter the channelized left-turn lane, instead of turning around both medians. A study by Allen, O'Hanlon, and McRuer (1977) also concluded that delineation contrast should be maintained above a value of 2.0 for adequate steering performance under clear night driving conditions. Studies of cross-traffic signing to address this problem have shown qualified but promising results in a number of jurisdictions (Gattis, 1996). (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. Age-related deficits in vision and attention are key to developing recommendations for improved stop control and yield control at intersections. 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. Burnham (1992) noted that signs located over the highway are more likely to be seen before those located on either side of the highway. Legibility distance was recorded at the point where subjects correctly read the word. (1995) reported that, compared with younger pedestrians, aging adults are overinvolved in crashes while crossing streets at intersections. M = (5730/D)* (1 - cos (SD/200)) Where: M = Distance from the center of the inside lane to the obstruction (ft.) D = Degree of the curve. Aging drivers may experience greater difficulties at intersections as the result of diminished visual capabilities such as depth and motion perception, as well as diminished attention-sharing (cognitive) capabilities. Design ADA Curb Ramps. Across all sites and crash severities, crashes were reduced by 39 percent in the after-conversion period. Freeway: high-speed, multi-lane divided highway Finally, the potential for wrong-way maneuvers, particularly by aging drivers, at intersections with positive offset channelized left-turn lanes was raised during a panel meeting comprised of aging driver experts and highway design engineers, during the conduct of the research performed by Staplin et al. Knoblauch, et al. The authors cited regression-to-the-mean as a factor in this crash reduction, but noted that the decline in pedestrian injury crashes was consistently greater with the countdown sites than the non-countdown sites. 1200 New Jersey Avenue, SEWashington, DC 20590 One of the slowest 15th percentile values (2.94 ft/s) was observed for older pedestrians crossing snow-covered roadways. And, even the mixed-case font that took up less sign space performed as well as the all-uppercase, Series D font, in terms of word recognition. An example of passive pedestrian detection technology is the "Pedestrian User-Friendly Intelligent" (PUFFIN) crossing in use in England (Department of Transport, 2006). Only 7.3 percent of the population had measured walking speeds 3 ft/s, and less than 1 percent had walking speeds of 4.0 ft/s. A detailed discussion of the outputs from the model exercise is provided in the publication Intersection Geometric Design and Operational Guidelines for Older Drivers and Pedestrians (Staplin, et al. An official website of the United States government Here's how you know. For the 495 signalized intersections in the State highway system, most samples represented a 4-year crash history (19831986). For the permissive indication, the sign appeared to help driver understanding, whereas during the overlap and protected indications it appeared to confuse drivers. The newly developed placard was installed at six intersections in Virginia, Maryland, and New York. The overall objective was to assess the understanding by West Virginia's aging drivers of traffic control devices and roadway design features associated with unsignalized at-grade intersections on high speed divided roadways. TheGreen Bookstates that although a right-angle crossing normally is desired, an angle of 60 degrees provides most of the benefits that are obtained with a right-angle intersection.
