Design Guidance for Intersection Auxiliary Lanes (2014) / Chapter Skim
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Pages 44-57
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From page 44... ...
44 Typical Designs Introduction As part of the questionnaire sent to key state transportation agencies, respondents were asked to identify locations with installations that would be considered best-practice sites. These best-practice sites were to demonstrate preferred design treatments for five design categories: island design, deceleration lane design, double left-turn lane design, triple left-turn lane design, and double right-turn lane design.
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45 • Regulation of traffic and indication of proper use of intersection. • Arrangements to favor a predominant turning movement.
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46 The distance to achieve a safe and comfortable speed at the point of convergence is based on the difference in speed between the operating speed on the turning roadway curve and the operating speed on the arterial. It is assumed that the operating speed on the turning roadway curve is 15 mph.
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47 full 20 ft width, followed by 170 ft of taper from 20 ft to 12 ft, followed by 200 ft of 12 ft width auxiliary lane. Corner Island Delineation.
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48 While this area is variable, based on local conditions, it is accepted that vehicles leaving a major roadway disrupt traffic flow, which affects overall operation and safety. Thus, good access management is critical in planning and designing a roadway so that it performs according to its functional classification.
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49 Intersection East Leg The development of the left-turn deceleration lane for traffic traveling westbound on State Route 42 was done symmetrically about the centerline at this location. The roadway cross-section approaching the intersection area consists of two 15-ft lanes (excluding curb and gutter)
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50 Design Considerations According to the Florida Manual of Uniform Minimum Standards for Design, Construction and Maintenance for Streets and Highways (referred to as the Florida Greenbook)
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51 speeds over 50 mph, the average running speed is used. Thus, for a design speed of 60 mph, the assumed entry speed is 52 mph.
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52 applied to double turn lanes, this skip striping is extended to the beginning of the outermost turn lane. At this location, this results in the skip striping being used from the beginning of the entering taper to 230 ft past the entering taper.
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53 at this location. To the north of this intersection, State Road 7 is a two-lane undivided arterial.
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54 Finally, the storage length accounts for the distance necessary to accommodate the number of vehicles likely to accumulate during a critical period. It is assumed that when two turning lanes are used, the storage length required is approximately half of what would be necessary for a single lane (note: not all states assume an even distribution of queue between the two provided turn lanes)
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55 to "provide approaching road users with positive identification" of the upcoming auxiliary lane and to provide for the greatest length of full-width auxiliary lanes to the extent possible. At this location, a taper of 100 ft is provided.
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56 volumes exceed 300 veh/hr) and how to account for offtracking and swept path widths and provides suggestions on the use of skip striping through the intersection for positive guidance.
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57 sufficient width to accommodate the development of the auxiliary lane. Additional guidance is necessary for illustrating the development of deceleration lanes for undivided roadways, resulting in a flared intersection.
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