Development of Left-Turn Lane Warrants for Unsignalized Intersections (2013) / Chapter Skim
Currently Skimming:
Pages 45-62
The Chapter Skim interface presents what we've algorithmically identified as the most significant single chunk of text within every page in the chapter.
Select key terms on the right to highlight them within pages of the chapter.
From page 45... ...
43 CHAPTER 3 LITERATURE REVIEW -- LEFT-TURN LANE DESIGN This chapter contains information on the design of left-turn lanes, reviewing information from state design manuals and national reference documents, as well as recent research. AASHTO GREEN BOOK MATERIAL AASHTO's Green Book (5)
|
From page 46... ...
44 applicable to both left- and right-turning lanes, but the approach speed is usually lower in the right lane than in the left lane. Storage Length The auxiliary lane should be sufficiently long to store the number of vehicles likely to accumulate during a critical period.
|
From page 47... ...
45 Width Median widths of 20 ft or more are desirable at intersections with single median lanes, but widths of 16 to 18 ft permit reasonably adequate arrangements. Where two median lanes are used, a median width of at least 28 ft is desirable to permit the installation of two 12-ft lanes and a 4-ft separator.
|
From page 48... ...
46 Table 33. Summary of left-turn lane design guidelines.
|
From page 49... ...
47 Entering Taper Length Two distinct tapers are defined in the state manuals: approach taper length and bay taper length. The approach taper length is commonly defined as V × W, where V = design speed (mph)
|
From page 50... ...
48 • The median width is equal to or greater than 40 ft, and only one left-turn lane in each direction on the mainline highway is required for capacity. • The current mainline ADT is 1500 or greater, and the left-turn DHV in each direction from the mainline is greater than 60 veh/hr.
|
From page 51... ...
49 • The design should be checked to ensure that conflicts are minimized between opposing left-turn maneuvers. When dual left-turn lanes are located opposite from an approach that does not have a dual leftturn lane, the design should minimize the lateral offset for vehicles traveling straight through the intersection.
|
From page 52... ...
50 Pedestrians Several states mention pedestrian considerations in the design of left-turn lanes. Arizona's guidelines state that when left-turn lanes are placed in raised (curbed)
|
From page 53... ...
51 Left-Turn Lane Length Kikuchi et al.
|
From page 54... ...
52 In a comparison of methods similar to Gard's, Lertworawanich and Elefteriadou (62) also developed a method to estimate storage lengths and compared it to the 2001 Green Book.
|
From page 55... ...
53 Municipalities and urban counties are increasingly adopting the use of taper lengths such as 100 ft for a single turn lane and 150 ft for a dual turn lane for urban streets (5)
|
From page 56... ...
54 its design; however, it is not sufficient to fully offset the turn lane (discussed below)
|
From page 57... ...
55 Source: Fitzpatrick, K., et al., Urban Intersection Design Guide, FHWA/TX-05/04365-P2. Copyright Texas Transportation Institute, The Texas A&M University System, College Station, Texas, 2005.
|
From page 58... ...
56 Table 35. Tarawneh and McCoy (66)
|
From page 59... ...
57 Source: A Policy on Geometric Design of Highways and Streets. Copyright American Association of State Highway and Transportation Officials, Washington, D.C., 2004.
|
From page 60... ...
58 associated with a lower level of comfort and a higher degree of difficulty perceived by drivers than an offset of −2.95 ft, even though the latter provides less sight distance. The study's authors speculated that this reaction might be because the −2.95-ft offset is more common than the 5.9-ft offset.
|
From page 61... ...
59 direct application of these models because left-turning vehicles' positions could be more flexible before crossing the opposing through traffic. Alternate Intersection Designs A number of alternate designs have been proposed and implemented to change the configuration of intersections to improve the efficiency and/or safety of turning movements.
|
From page 62... ...
60 design details in multilane roundabout design, including vehicle path alignment, lane widths, and positive guidance to drivers through the use of lane markings. SUMMARY OF LITERATURE Table 37 presents a summary of the left-turn lane design guidelines from the literature.
|
Key Terms
This material may be derived from roughly machine-read images, and so is provided only to facilitate research.
More
information on Chapter Skim is available.