Design Guidance for Intersection Auxiliary Lanes (2014) / Chapter Skim
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Pages 32-43
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32 State of the Practice Introduction As part of Task 2 efforts on NCHRP Project 3-102, the research team conducted a state-of-the-practice review of current design considerations. The focus of this sub-task was to identify those practices and evaluations not adequately documented in traditional literature.
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33 and ensure that their understanding was consistent with researchers' expectations. The remainder of this chapter contains the responses to the questionnaires, with summary comments to note trends and patterns in the respondents' answers.
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34 D-3. On which of the following is your agency's policy based?
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35 D-6. Please list up to three locations in your state with installations that you would consider "best practice" sites.
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36 Table 3-7 summarizes the responses to this question; respondents often had more than one component to their answers, and all responses are listed, so the summation is greater than the number of respondents.
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37 Storage Length Frequency (n=11) Site-by-site/traffic analysis 3 According to HCM 2 0.6 times single lane 1 Enough to avoid through vehicles blocking entrance 1 No guidance available 1 No answer 3 Deceleration Length Frequency (n=11)
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38 suggested that there might be conditions under which a sitespecific analysis of conditions would produce a triple left-turn as an alternative. The remaining respondents did not have such guidance and, in fact, often suggested that such treatments were discouraged or prohibited, typically because of truck traffic.
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39 3L-6. Please list up to three locations in your state with triple left-turn installations that you would consider "best practice" sites.
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40 appropriate adjustments to make. Answers are summarized in Table 3-15.
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41 Respondents provided a wide variety of answers, reflective of the open-ended nature of the question. Responses are summarized below: • Traffic islands can be beneficial in separating lanes of traffic, directing a traffic stream toward a specific direction, or providing pedestrian refuge areas.
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42 • Where the inner edges of pavement for right turns at intersections are designed to accommodate semitrailer combinations or where the design permits passenger vehicles to turn at 15 mph or more (i.e., 50 ft or more radius) , the pavement area at the intersection may become excessively large for proper control of traffic.
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43 I-6. Do you have sites that are less than optimal?
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