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42 Guidelines for Selection of Speed Reduction Treatments at High-Speed Intersections 4.5.3 Treatment Layout/Design The placement and dimensions of longitudinal rumble strips on high-speed intersection approaches should be determined through a combined review of field conditions, driver sight lines and desired response, and local practice and judgment. The distance that the treatment extends from the intersection proper should be related to stopping sight distance and/or the distance required to achieve the desired deceleration at a com- fortable deceleration rate. The distance should also be selected to work in concert with other treatments or features, such as warning signs. The markings have the potential to draw additional attention to those warning signs and to encourage drivers to reduce their speeds as they approach the intersection. The dimensions of the rumble strips will vary by application. If the treatment is being used to nar- row the functional width of the approach lane, the treatment should extend beyond the existing striping. Consideration of truck traffic is likely to constrain the amount of narrowing that may occur. Treatment design considerations related to the types of rumble strips (raised, milled, etc.) were discussed previously in Section 4.4.3. 4.5.4 Speed Effects No documentation was found regarding the speed effects of longitudinal rumble strip appli- cations in segment or intersection locations. However, it is expected that longitudinal rumble strips have the greatest potential to reduce speeds when they are used to narrow the functional width of the roadway. FHWA is conducting research into these applications. However, this study applied multiple treatment types at a given location and, therefore, the direct effects of the rum- ble strips are not documented. At non-intersection locations on two-lane highways, one study found that the presence of cen- terline rumble strips had no effect for sites with 11- and 12-ft lanes. (Porter et al., 2004) 4.5.5 Safety Effects Safety improvements have been documented at locations where continuous or shoulder rum- ble strips were installed along roadway segments However, there has been no documentation to show the results of this specific application at intersection approaches. Shoulder rumble strips have proved to be a very inexpensive and effective treatment to reduce run-off-road crashes. Reports from Maine, New York, and California have reported run- off-road crash reductions of 20%-72% after continuous shoulder rumble strips were installed. (Corkle et al., 2001) Similarly, centerline rumble strips have been shown to improve safety along undivided highways. A study analyzing the safety effectiveness of centerline rumble strips along approximately 210 miles of treated roads in seven states found a 14% reduction for all injury crashes combined, as well as a 25% reduction for frontal and opposing-direction sideswipe injury crashes. (Persaud et al., 2004) 4.6 Wider Longitudinal Pavement Markings 4.6.1 Overview No test sites provided documented applications for the high-speed intersection treatments discussed in this section. Wider longitudinal pavement markings increase intersection visibility
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Treatment Descriptions 43 and attract driver attention to the intersection ahead. These treatments can be applied to address the needs of older drivers and a lack of driver expectancy. Design variations include marking width, length, and reflectivity. A secondary effect of these treatments is that speed may increase with increased visibility. 4.6.2 Applicability and Considerations Many transportation departments increase the width of pavement markings to improve the visibility of centerline, lane line, and edge-line striping, which can provide added guidance to drivers from greater distances. (Gates and Hawkins, 2002) Although no documentation for wider longitudinal pavement marking applications at intersection approaches was found, this treatment may be an effective speed reduction treatment for some high-speed intersections because it may increase driver awareness of the presence of an intersection and help reinforce the need for drivers to operate differently at the intersection than in the roadway segment. The most common reasons that jurisdictions apply wider longitudinal pavement markings are to improve visibility, assist older drivers, and reduce crashes. Many transportation depart- ments have policies to apply wider longitudinal pavement markings to routes of a certain road- way classification--most commonly access-controlled highways. Some jurisdictions have policies that require using wider edge lines on all state routes while others install this treatment exclusively at hazardous locations that could benefit from greater driver visibility. (Gates and Hawkins, 2002) Wider longitudinal pavement markings (see Exhibit 4-11) assist peripheral vision by improv- ing the peripheral signal, thus decreasing driver workload and increasing driver comfort and performance. The largest visibility benefit is seen with older drivers, because visual and cogni- tive capabilities decline with age. (Gates and Hawkins, 2002) The higher cost of wider longitudinal pavement markings may be somewhat offset by greater durability. Pavement lighting systems are an alternative to wider longitudinal pavement markings that serve the same function, and may have similar effects. This treatment does require a power source that may require maintenance or replacement over time. 4.6.3 Treatment Layout/Design The placement and dimensions of wider longitudinal pavement markings on high-speed intersection approaches should be determined through a review of field conditions, driver sight lines and desired response, and local practice and judgment. Exhibit 4-11. Wider longitudinal pavement markings in France.