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20 Guidelines for Selection of Speed Reduction Treatments at High-Speed Intersections Mid-Block Target Perception Deceleration Total Speed (Vs) Approach Reaction Distance Transition Speed (Va) Distance (feet) Distance (mph) (feet) (feet) 60 45 220 390 610 60 20 220 620 840 55 45 200 280 480 55 20 200 500 700 50 45 185 240 425 50 20 185 480 665 45 35 165 225 390 45 20 165 350 515 Notes: Vs is the average speed of the segment. Va is the target approach speed. Perception and reaction time is assumed at 2.5 seconds. Deceleration distances are interpreted from Chapter 10: Grade Separations and Interchanges. (AASHTO, 2004) Exhibit 3-3. Transition distance between segment and intersection area. 3.4 Combining Treatments Intuition suggests that combining treatments will increase the potential to reduce speed. Although there is little research that determines this potential, it is expected that combining treatments will have a benefit up to a point, after which, no more speed reduction will occur. This is because drivers will operate at a speed at which they feel comfortable or safe. Below this speed, the cumulative application of treatments becomes ineffective. Additional treatments can provide benefits by reinforcing the need to be prepared to slow down, even if additional speed reduction is not observed. An example of combining treatments is a low-cost concept for two-way, stop-controlled intersections on high-speed, two-lane rural highways as studied by FHWA and documented in Low-Cost Intersection Treatments on High-Speed Rural Roads. (FHWA, 2006) As shown in Exhibit 3-4, the concept incorporates a variety of individual treatments, including lane nar- rowing, splitter islands on each approach, and lateral pavement markings on each side of the traveled way. The objectives of this FHWA study were to identify, promote, and evaluate low-cost concepts to reduce speeds at intersections. The research team investigated two concepts that combined various roadway treatments. The first concept was to reduce the lane width, add rumble strips, and add pavement markings on the major road. The second concept was to install a mountable splitter island with stop signs on the minor road approaches. The treatment concepts were implemented in multiple locations in Pennsylvania, New Mexico, and Illinois. The results from this study showed statistically significant speed reduction at all sites. The combination of treatments reduced all vehicle speeds by an average of 3 mph, and reduced the 85th-percentile speeds by 4 mph. In addition, testing results for trucks revealed an average speed reduction of 5 mph and a reduction in the 85th-percentile speeds of 4 to 5 mph. (FHWA, 2006) The team collected crash data for five years before deployment and will collect data for two years after deployment to determine whether these treatments yield quantifiable results. The team also plans to analyze crash data at the various sites at the project's end in June 2009 because