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Treatment Descriptions 33 after a three-month acclimation period. At the perceptionreaction data collection locations, mean speeds were reduced by 2.3 mph. At the accident avoidance data collection locations, mean speeds were reduced by 2.8 mph. During a study of warning signs installed at two high-speed intersection sites in Texas, Ullman and Rose (2004) recorded an initial reduction of 3 to 4 mph at both sites, with one site sustain- ing the lowered speeds after the novelty effect of the sign diminished. Studies examining the effectiveness of speed displays at rural interstate work zones in South Dakota and Virginia found that the speed monitoring displays reduced mean vehicle speeds by 1.4 to 4 mph within the work zones and reduced the number of vehicles speeding through the work zone by 20%-40%. Maze et al. (2000) concluded that sign placement can impact the effec- tiveness of this treatment. A study of three dynamic curve warning systems installed on ramps in Virginia and Maryland showed that the three systems significantly influenced truck speeds--drivers reduced their speeds if they had exceeded the maximum safe speed. (Torbic et al., 2004) In the field evaluation of the CCS installed in Prince William County, Virginia, it was observed that the CCS resulted in lower intersection approach speeds and longer projected times to colli- sion. (Hanscom, 2001) 4.2.5 Safety Effects No documentation of the safety benefits of dynamic warning systems at intersection approaches was found. However, the study of dynamic curve warning systems in Maryland and Virginia identified that prior to installation there had been 10 truck rollover crashes and after three years in operation, no rollover crashes had been reported. 4.3 Transverse Pavement Markings 4.3.1 Overview Five NCHRP Project 3-74 test sites in Oregon provided documented applications for the high-speed intersection treatments discussed in this section. Transverse pavement markings improve visibility and driver attention. These treatments can be applied to provide visual cue reinforcements to changing conditions and the need to reduce speed. Design variations include peripheral or full transverse lines. Long-term effectiveness and driver familiarity should be considered. 4.3.2 Applicability and Considerations As defined by the MUTCD, transverse pavement markings are "pavement markings that are generally placed perpendicular to and across the flow of traffic." (FHWA, 2003, p. 1A-14) Peripheral transverse lines, as shown in Exhibit 4-4, involve bars only at the edge of a travel lane, instead of bars extending across the travel lane. Transverse chevrons are painted geometric arrows that converge to give the illusion of speed. (Griffin and Reinhardt, 1995) Transverse pave- ment markings are commonly used in speed management to reinforce the need to reduce speed or to warn drivers of an approaching condition that may require vehicular maneuvers. Common applications of transverse pavement marking locations include approaches to traffic circles and intersections, horizontal curves, construction areas, bridges, and freeway off-ramps. (Griffin and Reinhardt, 1995) Transverse pavement markings have also been placed at locations

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34 Guidelines for Selection of Speed Reduction Treatments at High-Speed Intersections Exhibit 4-4. Peripheral transverse pavement markings. where excessive speed was a contributor to crashes and other speed reduction treatments had not been effective. (Agent, 1980) Peripheral transverse lines require less maintenance than transverse lines that extend across the travel lane because most drivers do not track over the markings. (Human Factors North, Inc., 2002) Transverse pavement markings have no known impact to multimodal users--it is not expected that multimodal users would be adversely affected by transverse pavement markings. 4.3.3 Treatment Layout/Design Transverse pavement markings should be placed in a location that provides adequate advance warning time for drivers to reduce their speeds appropriately. The placement of transverse pave- ment markings that is optimal to reduce speeds on intersection approaches has not been quan- tified. The "Green Book" (AASHTO, 2004) values for deceleration may provide a starting point in locating transverse pavement markings. Transverse pavement lines may be installed in several small clusters on a high-speed intersec- tion approach. The number of lines, their spacing, and the distance from the intersection proper should be determined through a combination of a review of field conditions, driver sight lines and desired response, and local practice and judgment. As guidance, the MUTCD suggests, ". . . because of the low approach angle at which pavement markings are viewed, transverse lines should be proportioned to provide visibility equal to that of longitudinal lines." (FHWA, 2003, p.1A-14) The appropriate location and length of the lines depends on the speed at which the driver is traveling, the deceleration rate, and the driver's perceptionreaction time. (Agent, 1980) Appropriate installation points may be selected to reinforce other new or existing treatments or features on the intersection approach such as warning signs, shoulder markings, parking space markings, and pavement legends (SLOW DOWN, REDUCE SPEED, etc.), and at the intersec- tion proper (such as lane-use legends, stop lines, crosswalk lines, and others). The transverse pavement markings have the potential to draw additional attention to those signs and markings and to encourage drivers to reduce their speeds as they approach the intersection. Other appro- priate locations for treatment installation may include the stopping sight distance for the approach speed, or a point where the roadway environment changes, such as at the point of

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Treatment Descriptions 35 tangency or at a driveway. Appendix B describes and illustrates the treatment layout for one of the NCHRP Project 3-74 research test sites. The spacing of the transverse bars and transverse chevrons may reflect the desired travel speeds of the vehicles on the roadway. Some applications of transverse bars have used a rate of advance- ment of two stripes per second. In some applications transverse bars are spaced progressively closer together at an increasing rate as the driver travels along the roadway. When applied in this way, the bars are referred to as optical speed bars. The intent is that the reduced spacing gives the driver the perception of acceleration, causing the driver to slow down; however, there are no data to support this claim. (Agent, 1980) 4.3.4 Speed Effects After a 90-day acclimation period, transverse pavement markings were found to reduce speed marginally at four high-speed intersection approaches tested through NCHRP Project 3-74. Overall, the markings reduced mean speeds by 0.6 mph (standard error of 0.3 mph). Addition- ally, at the perceptionresponse time data collection locations, transverse pavement markings were found to reduce mean speeds by 0.9 mph (standard error of 0.4 mph). Studies of segment applications of transverse pavement markings have reported reduced mean and 85th-percentile speeds on the order of 20%-30%. (Katz et al., 2003; Griffin and Reinhardt, 1995) At the Newbridge Roundabout in Scotland, transverse pavement markings resulted in reduced mean and 85th-percentile speeds. The overall mean speed throughout the day was reduced by approximately 23%, and the overall 85th-percentile speed throughout the day was reduced by approximately 30%. (Katz et al., 2003) In a study conducted on US Highway 60 in Meade County, Kentucky, transverse bar pave- ment markings were placed prior to a sharp curve with a high crash rate. This study revealed that the treatment became less effective as a speed reduction technique as drivers became familiar with the treatment. Furthermore, the long-term effects during the nighttime were less than the long-term effects during the day. (Agent, 1980) Research by Godley et al. (2000) using a driving simulator found that transverse lines with both constant and reducing spacing (i.e., optical speed bars) lowered speeds. The research deter- mined that speed perception was not influenced by the decreased spacing of the lines. Addi- tionally, Godley found that the peripheral transverse lines induced speed reduction almost as effectively as full transverse lines. No studies have been found that evaluate the effectiveness of the transverse chevron markings with respect to speed. 4.3.5 Safety Effects No published data were found to address the effects of transverse pavement markings on safety at conventional intersections. Safety improvements associated with segment or roundabout applications of transverse pavement markings were reported by each of the studies referenced below. In 1993, a study in Osaka, Japan, reported that converging chevron pavement markings on the Yodogawa Bridge were more effective than conventional signing in helping to prevent crashes at a high-crash location. No crashes resulting in injuries occurred in the two years after the chevron markings were installed. In the past, the bridge had a history of crashes causing injuries and fatalities. (Griffin and Reinhardt, 1995)