Low Cost Safety Improvements Pooled Fund Study

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Low Cost Safety Improvements Pooled Fund Study

• Offset Left-Turn Lanes

Nancy Lefler, VHB
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Overview

• Background
• Status of Data Collection
• Remaining Data Needs
• Evaluation Considerations

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Background

• Ranked 12th
• NCHRP Report 500 Series
• Older Driver Guidebook
• Left-turn maneuvers
• Improved sight distance
• Beneficial to left-turning vehicles
• Particularly older drivers
• (Stapin et al., 1997)

Photo Source NCHRP Report 500 Series Volume 9
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Background

• Tried
• Moderate to high-cost
• Depends on available right-of-way and median
  width
• Moderate implementation
• 2-4 years depending on right-of-way and median
  width
• Potential difficulties
• Initial driver confusion
• Advance signs and pavement markings
• Key to success
• Identify appropriate intersections

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Data Collection
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Status of Data Collection

• Nebraska
• Blanketed strategy in Lincoln
• 184 strategy sites included in study
• Reference sites from Omaha
• Crash data obtained from NE DOR

Photo Source NCHRP Report 500 Series Volume 9
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Status of Data Collection

• Iowa
• 12 strategy sites included in the study
• Reference sites from recent intersection study
• Florida
• Only 7 sites so far need at least 12
• Currently searching for additional sites
• Crash data obtained from FLDOT

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Remaining Data Needs

• Nebraska
• Geometric data for study sites
• Iowa
• Iowa collecting roadway, traffic, and crash data
  for treatment and reference sites
• Florida
• Additional study sites
• Similar reference sites (signalized with
  permitted)
• Intersection data for strategy and reference sites

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Evaluation Considerations

• Aggregate analysis
• Crash-based evaluation
• Empirical Bayes before-after study design
• Evaluate each State individually and combined
• Individual analysis depends on data availability
• Disaggregate analysis
• Depends on variation in sample
• Depends on sample size

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QUESTIONSorCOMMENTS