Analysis of Naturalistic Driving Study Data: Offset Left-Turn Lanes (2014) / Chapter Skim
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From page 6... ...
6C h a p t e r 2 This chapter describes offset left-turn lanes, presents an overview of the relevant literature, and discusses how NDS data were used to provide new insights into driver behavior at opposing left-turn lanes. Background: What are Offset Left-turn Lanes and how Do they Function?
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7Figure 2.1. Sight-obstructed regions for unpositioned and positioned vehicles at intersection without offset left-turn lanes.
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8typically used striping treatments to narrow or shift the leftturn lane to provide offsets that were slightly less negative. The treatments in Wisconsin were found to reduce all crashes by 34%, injury crashes by 36%, and left-turn crashes by 38%, while the treatments in Florida and Nebraska showed no crash reduction.
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9the gaps that are available, the time spent waiting to turn, lighting, pavement and weather conditions, the turning driver's perception of the speed and distance of the oncoming vehicles, the driver's perception of his own and his vehicle's capabilities, the driver's familiarity with the intersection or similar intersections, and the driver's tolerance for risk. To assist left-turning drivers in evaluating adequate gaps in oncoming traffic, researchers in California conducted a study of gap-acceptance behavior at five intersections to develop guidance for when an Intersection Decision Support System should alert drivers about gaps in oncoming traffic.
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10 participants under age 30 allowed the smallest gaps, those over age 59 were the least consistent judges and were slower to clear the next lane when turning right. Older drivers may be at higher risk at intersections, especially when approaching traffic exceeds 100 km/h, through failure to detect approaching vehicles, poor speed and gap estimation once vehicles are detected, and slower lane clearance when turning (Parsonson et al.
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11 driver's perspective. Other studies that have evaluated sight obstructions related to opposing left-turn lanes have simply used the presence of an opposing left-turn vehicle as a surrogate for sight-distance restrictions, or they have used physical models to calculate sight distance based on assumptions about each driver's position.
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