LOW COST SAFETY IMPROVEMENTS Practitioner Workshop The Tools – Identification of High Crash Locations – Session #2

Identification of High Crash Locations Learning Objectives:  Describe the HSIP Planning Process  Crash Mitigation Process  Identify appropriate Engineering Countermeasures from Crash Patterns

HSIP Planning Detailed Engineering Study Document the Analysis Project Selection, Implementation, & Evaluation Document the Evaluation Network Screening or Site Selection List of Sites for Review

What is Network Screening?  Highway network system made up of segments and intersections  Network screening is a systematic examination of all entities  Purpose: To rank all entities, based on selected criteria, in order to conduct detailed safety studies Money should go where it achieves the greatest effect in terms of preventing crashes and reducing their severity

Identification of High Crash Locations The six steps in the crash mitigation process

1.Identify Sites 2.Collect Crash Experience 3.Gather Field Conditions 4.Identify Contributing Factors and Countermeasures 5.Assess and Select Countermeasures 6.Implement and Evaluate

Identification of High Crash Locations Step 1: Identify Sites with Potential Safety Problems Crash data Traffic Measures Field Observations Complaints Enforcement input Surrogate measures

Identification of High Crash Locations Step 1: Identify Sites with Potential Safety Problems Crash data  Total Number of Crashes  Crash Density (Crashes per mile)  Crash Rate (Crashes per million vehicle miles)  Number Quality Control  Rate Quality Control  Crash Severity  Severity Index  Crash Index

Most Common Reporting Errors  Crash location  Direction of travel  Driver action  Pedestrian condition  Vertical road characteristics

Conventional Screening  Conventional techniques of screening in use are known to have difficulties in identifying ‘ unsafe ’ sites: ð Crash counts = bias to high volume sites ð Crash rates = bias to low volume sites ð Crash rates ’ assumption of linearity is invalid ð Regression-to-mean (RTM) effect if sufficient allowance is not made for random errors

Identification of High Crash Locations Roadway Segment: CR = N / [ADT x 365 x L x ] where CR is expressed as “Crashes per million vehicle miles (or kilometers)” and N = Number of crashes per year ADT = Average Daily Traffic L = Length of segment (mi or km)

Identification of High Crash Locations Example: For N = 50 crashes for 3 year period ADT = 3,000 Average Daily Traffic L = 2.8 miles CR = N / [ADT x 365 x L x ] CR = 50 / [3,000 ADT x 3 yrs x 365 x 2.8 miles x ] CR = 5.43 crashes per million vehicle miles

Identification of High Crash Locations Different Hwy Types Experience Different Crash Rates

Identification of High Crash Locations Step 1: Identify Sites with Potential Safety Problems *From Mn DOT Traffic Safety Fundamentals Handbook

Identification of High Crash Locations Intersection: AR = N / {[Sum (ADT)s /2] x 365 x 10 -6} where AR is expressed as “crashes per million entering vehicles” and N = Number of crashes per year Sum (ADT)s = Sum of all Average Daily Traffic entering the intersection

Identification of High Crash Locations Example: For N = 25 crashes for 3 years ADT (N) = 10,000 ADT (S) = 9,000 ADT (E) = 3,500 ADT (W) = 4,000 Sum (ADT)s=(10,000+9,000+3,500+4,000) = 26,500 AR = N / {[Sum (ADT)s /2] x 365 x 10 -6} AR = 25/ {26,500/2] x 3 yrs x365 x 10 -6} AR = 1.72 crashes per million entering vehicles

Identification of High Crash Locations Collision Types at Rural Intersections

Identification of High Crash Locations Intersection Crash Rates Average of 1.5 crashes per year for Un- Signalized Intersections in rural areas– recent California analysis* Average of 2.5 crashes per year in urban areas *NCHRP 500, Volume 5: A Guide for Addressing Unsignalized Intersection Collisions, 2003.

Identification of High Crash Locations Step 2: Characterize the Crash Experience Prepare a Collision Diagram

Step 3: Characterize Field Conditions Identification of High Crash Locations

Step 3: Characterize Field Conditions Traffic Data Studies: Identification of High Crash Locations  Traffic Volume – Turning Movement, ADT  Spot Speeds  Traffic Conflict Study  Sight Distance Evaluation

Non-Crash Based Procedures Identification of High Crash Locations

Step 4: Identify Contributing Factors and Appropriate Countermeasures Identification of High Crash Locations *Table 12, from Missouri HAL Manual

Step 5: Assess Countermeasures and Select Most Appropriate Identification of High Crash Locations

Probable Causes for Crash Patterns and Engineering Countermeasures Identification of High Crash Locations Rear-End Collisions at un-signalized intersection

Identification of High Crash Locations Documents list “Crash Reduction Factors” (CRF) and “Accident Modification Factors” (AMF) for specific types of crashes –CRF : (+) number is % reduction in crash type (-) number is % increase in crash type

Identification of High Crash Locations “Accident Modification Factors” (AMF) for specific types of crashes –AMF : ratio of (after) crashes / (before) crashes AMF < 1 means a reduction in crash type AMF > 1 means an increase in crash type – AMF = 1- CRF

Estimated Crash Reduction Factors Identification of High Crash Locations Install Warning Signs

Estimated Crash Reduction Factors Identification of High Crash Locations * From MN DOT Traffic Safety Fundamentals Handbook

Traffic Crash Costs: Identification of High Crash Locations *NCHRP 440

Traffic Crash Costs: Identification of High Crash Locations * From MN DOT Traffic Safety Fundamentals Handbook

Typical Benefit/Cost Ratios Identification of High Crash Locations * From MN DOT Traffic Safety Fundamentals Handbook

Step 6: Implement Countermeasures and Evaluate Effectiveness Identification of High Crash Locations Improve Sight Distance – 5% Crash Reduction per Quadrant – 20% for all 4 quadrants

Identification of High Crash Locations Review Questions:  What are the six steps in the crash mitigation process?

Questions? Identification of High Crash Locations