Effectiveness of Median Cable Barriers and Rumble Strips Chris Poole, Iowa Department of Transportation Peter Savolainen, Iowa State University Mid-Continent Transportation Research Symposium August 16, 2017 1
Project Objectives Median Cable Barrier Examine impacts of median cable barrier in Iowa Estimate cost-effectiveness Develop guidelines for subsequent installations Rumble Strips Assess impacts of installing rumble strips on narrow pavements Develop guidance for installation of centerline and/or shoulder rumble strips 2
Introduction Cable Barrier Roadside Design Guide (AASHTO) recommends median barriers to mitigate cross-median crashes Cable barrier benefits: Lower installation cost Forgiving in a crash Less snow drift Iowa installation program Began in 2003 Currently 320 miles of cable installed Estimated 340 miles by end of 2018 3
Fatality Trend 4
Data Collection Roadway Information Cable barrier installation locations Annual average daily traffic (AADT) Median width Shoulder width Barrier offset 5
Crash Data Review: Crash Codes vs. Narratives Identification of median-related crashes by two methods: Crash code logic Crash report narrative Dataset Severity Level Min Max Mean K (Fatal) 0 2 0.013 A (Incapacitating) 0 2 0.031 Identified by B (Non-incapacitating) 0 3 0.093 Crash Codes C (Possible Injury) 0 4 0.114 O (No Injury) 0 11 0.636 Total 0 13 0.886 Identified by Crash Narratives K (Fatal) 0 2 0.016 A (Incapacitating) 0 2 0.036 B (Non-incapacitating) 0 3 0.105 C (Possible Injury) 0 4 0.132 O (No Injury) 0 12 0.720 Total Crashes 0 15 1.009 6
Impacts on Crashes by Injury Severity Level K-injury crashes per mile per year 0.10 0.08 0.06 0.04 0.02 0.00 0 20,000 40,000 60,000 80,000 Annual Average Daily Traffic (veh/day) A-injury crashes per mile per year 0.16 0.14 0.12 0.1 0.08 0.06 0.04 0.02 0 0 20,000 40,000 60,000 80,000 Annual Average Daily Traffic (veh/day) B-injury crashes per mile per year 0.5 0.4 0.3 0.2 0.1 0 0 20,000 40,000 60,000 80,000 Annual Average Daily Traffic (veh/day) Before After Before After Before After C-injury crashes per mile per year 1 0.8 0.6 0.4 0.2 0 0 20,000 40,000 60,000 80,000 Annual Average Daily Traffic (veh/day) Before After O-injury crashes per mile per year 6 5 4 3 2 1 0 0 20,000 40,000 60,000 80,000 Annual Average Daily Traffic (veh/day) Before After Crash Severity Average Change K (Fatal) -56.0% A (Incapacitating) -25.9% B (Non-incapacitating) -18.9% C (Possible Injury) +15.0% O (No injury) +141.1% 7
Benefit/Cost Analysis Economic Factors Installation costs Maintenance costs Crash costs Discount rate Design life 8
Maintenance/Repair Costs Installation costs $49,594 per mile Maintenance costs Average $1.2M per year $1750 per reported crash Mobilization as Percent of Total Cost 45.0% 40.0% 35.0% 30.0% 25.0% 20.0% 15.0% 10.0% 5.0% 0.0% 2011 2012 2013 2014 2015 Year 9
Crash Cost Savings Pre-Barrier Crashes per 100MVMT Post-Barrier Crashes per 100MVMT Crashes Saved Per Year Crash Type Fatal 0.321 0.141 5.52 Incapacitating 0.649 0.481 5.16 Non-Incapacitating 1.693 1.373 9.83 Possible Injury 2.028 2.332-9.34 Property Damage Only 8.813 21.248-381.94 Crash Type Iowa DOT Cost per Injury Iowa DOT Cost per Crash Fatal $ 4,500,000 $ 5,382,353 Incapacitating $ 325,000 $ 402,511 Non-Incapacitating $ 65,000 $ 86,141 Possible Injury $ 35,000 $ 43,476 Property Damage Only $ 7,400* $ 18,558 *Cost per crash 10
Sensitivity Analysis Factors Considered Crash costs Economic vs. comprehensive Iowa DOT vs. NSC Maintenance costs $500 $2000 (Avg. cost of $1750 per reported crash) Discount rate 3% 6% (Iowa DOT = 4%) Design life 15 30 years (Iowa DOT = 20 yrs) 11
B/C Analysis Results 25.0 23.8 20.0 18.4 18.5 Benefit/Cost Ratio 15.0 10.0 5.0 12.9 14.7 16.3 17.7 15.3 14.7 14.2 13.6 4.0 14.7 15.1 12.8 0.0 15 20 25 30 3 4 5 6 NSC Econ. Iowa DOT NSC Comp. 500 1000 1500 2000 Design Life (years) Discount Rate (%) Crash Cost Cost per Repair ($) 12
Implementation Median Cable Planning to continue with new installations High B/C ratios Favorable CMFs Improved public opinion Working with ISU to identify high/med/low priority corridors for expansion Apply methodology to expressways 13
Introduction Rumble Strips Iowa DOT Design Manual, Section 3C-5 Centerline Rumble Strips (CLRS) Two-lane primary roads with > 3,000 ADT, 11-ft lanes, and 2-ft shoulders Shoulder Rumble Strips (SRS) Normally not placed on paved shoulders < 4 ft 14
Field Studies of Driver Behavior Trailer-mounted data collection units HD video cameras Radar sensor Solar panel 15
Encroachment Rates by Rumble Strip Installation Type Edgeline encroachment rate per 1000 vehicles 2 1.5 1 0.5 0 10 10.5 11 11.5 12 Lane width (ft) Centerline and shoulder Shoulder Only Edgeline Only No rumble strips Centerline encroachment rate per 1000 vehicles 2 1.5 1 0.5 0 10 10.5 11 11.5 12 Lane width (ft) Centerline and shoulder Edgeline No rumble strips 16
Analysis of Rumble Strip Impacts on the Primary Network 17
Iowa Impacts on Cross-Centerline Crashes 0.25 Crashes Per Mile Per Year 0.2 0.15 0.1 0.05 CRF = 33.2% 0 0 500 1000 1500 2000 2500 3000 Annual Average Daily Traffic (AADT) Without Centerline Rumble Strips With Centerline Rumble Strips 18
Iowa Impacts on Cross-Edgeline Crashes 0.25 Crashes Per Mile Per Year 0.2 0.15 0.1 0.05 CRF = 16.1% 0 0 500 1000 1500 2000 2500 3000 Annual Average Daily Traffic (AADT) Without Edgeline Rumble Strips With Edgeline Rumble Strips 19
Crash-Based Guidance for Centerline Rumble Strip Installation 20
Crash-Based Guidance for Edgeline/ Shoulder Rumble Strip Installation 21
Economic Analysis Installation costs obtained from Bid Express (Iowa DOT) Crash costs from Highway Safety Manual (AASHTO 2010) Installation Rumble Strip Types Cost (per mile) Shoulder Rumble Strips (both sides) $4,551.36 Centerline Rumble Strips $2,095.63 Centerline and Shoulder Rumble Strips $6,646.99 Injury Severity Comprehensive Level Crash Cost Fatality (K) $4,008,900 Disabling Injury (A) $216,000 Evident Injury (B) $79,000 Possible Injury (C) $44,900 PDO (O) $7,400 22
Benefit/Cost Ratio 300 200 100 0 0 500 1000 1500 2000 2500 3000 Annual Average Daily Traffic Shoulder Centerline Centerline and Shoulder Benefit/Cost Ratio for Wide Lanes/Shoulders Benefit/Cost Ratio 300 250 200 150 100 50 0 0 500 1000 1500 2000 2500 3000 Annual Average Daily Traffic Shoulder Centerline Centerline and Shoulder Benefit/Cost Ratio for Narrow Lanes/Shoulders 23
Implementation Rumble Strips Statewide CLRS retrofit project Seek changes in DOT policy/guidance: CLRS on all routes, regardless of volume ELRS even where shoulder is not paved County safety funding program stipulations: CLRS and SRS where paved top 26 ft or greater CLRS or SRS where paved top less than 26 ft 24
Comments or Questions? Chris Poole, P.E. Safety Programs Engineer Iowa Department of Transportation Phone: (515) 239-1267 E-mail: Chris.Poole@iowadot.us Peter Savolainen, Ph.D., P.E. Associate Professor Iowa State University Civil, Construction, and Environmental Engineering Phone: (515) 294-3381 E-mail: pts@iastate.edu 25