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Safety management software for state and local highway agencies: Improves identification and programming of site-specific highway safety improvements Incorporates state-of-the-art safety management approaches with computerized analytical tools http://www.safetyanalyst.org/.

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slide2
Safety management software for state and local highway agencies:
    • Improves identification and programming of site-specific highway safety improvements
    • Incorporates state-of-the-art safety management approaches with computerized analytical tools

http://www.safetyanalyst.org/

who is developing safetyanalyst
Who is DevelopingSafetyAnalyst?
  • Federal Highway Administration
  • Technical Working Group
    • 19 participating (pooled-fund) States
    • 1 local highway agency
    • 2 MPOs
safetyanalyst modules
SafetyAnalyst Modules

Module 1 – Network Screening

Module 2 – Diagnosis and Countermeasure Selection

Module 3 – Economic Appraisal and Priority Ranking

Module 4 – Countermeasure Evaluation

status of development
Status of Development
  • Module 1 - Network Screening
    • Beta testing of interim version underway
  • Module 2 - Diagnosis and Countermeasure Selection
    • Interim version available for testing Dec 2006
  • Module 3 - Economic Appraisal and Priority Ranking
    • Interim version available for testing Dec 2006
  • Module 4 – Countermeasure Evaluation
    • Beta testing of interim version underway
advantages of safetyanalyst over existing techniques
Advantages of SafetyAnalyst over Existing Techniques
  • Integrates/automates all parts of safety management process
  • Applies state-of-the-art analytical procedures
  • Strong cost-effectiveness component

…Enables engineers to make more informed decisions more efficiently

module 1 objectives
Module 1 - Objectives
  • Screen entire roadway network, or portion of network, and to identify sites with potential for safety improvement
  • Rank sites with potential for safety improvement
  • Select sites for further investigation within Module 2 - Diagnosis and Countermeasure Selection
types of network screening
Types of Network Screening
  • Basic network screening
    • With Peak Searching on roadway segments
    • With Sliding Window on roadway segments
  • High proportion of specific accident type
  • Sudden increase in mean accident frequency
  • Steady increase in mean accident frequency
  • Corridors with promise
basic network screening
Basic Network Screening
  • Uses Empirical Bayes methodology
    • Combine observed and predicted accidents
  • Expected accident values expressed as:
    • Expected accident frequency
    • Excess accident frequency
  • Two screening approaches for roadway segments
    • Peak searching
    • Sliding window
basic network screening with peak searching on roadway segments
Basic Network Screening:(with Peak Searching on Roadway Segments)
  • For roadway segments, individual sites are divided into windows of size 0.1 mi
    • Accident frequencies are calculated for each window within a site
  • Windows are flagged when:
    • Expected value greater than user-specified limit
    • Expected value is statistically reliable
  • If no windows are flagged, incrementally increase window size by 0.1 mi and test again
  • More than one window pertaining to a site can be flagged
  • Rank order site based upon expected or excess accident frequencies
peak searching concepts

0.0 mi

0.1 mi

0.2 mi

0.3 mi

0.4 mi

0.5 mi

0.6 mi

0.67 mi

Peak Searching Concepts

Roadway Segment

Win # 1

Win # 2

0.03 mi

0.07 mi

Win # 3

Win # 4

Note:

Window length = 0.1 mi

Expected accidents = (acc/mi)

Limiting Value = 5 acc/mi

CVLimit = 0.5

Win # 5

Win # 6

Win # 7

peak searching concepts14

Roadway Segment

0.03 mi

0.0 mi

0.1 mi

0.2 mi

0.3 mi

0.4 mi

0.5 mi

0.6 mi

0.67 mi

Win # 1

0.07 mi

Win # 2

Win # 3

Win # 4

Win # 5

Win # 6

Peak Searching Concepts

Note:

Window length = 0.2 mi

Expected accidents = (acc/mi)

Limiting Value = 5 acc/mi

CVLimit = 0.5

peak searching concepts15

Roadway Segment

0.0 mi

0.1 mi

0.2 mi

0.3 mi

0.4 mi

0.5 mi

0.6 mi

0.67 mi

Win # 1

Win # 2

Win # 3

Win # 4

Win # 5

Peak Searching Concepts

Note:

Window length = 0.3 mi

Expected accidents = (acc/mi)

Limiting Value = 5 acc/mi

CVLimit = 0.5

peak searching concepts16

Roadway Segment

0.0 mi

0.1 mi

0.2 mi

0.3 mi

0.4 mi

0.5 mi

0.6 mi

0.67 mi

Win # 1

Win # 2

Win # 3

Win # 4

Peak Searching Concepts

Note:

Window length = 0.4 mi

Expected accidents = (acc/mi)

Limiting Value = 5 acc/mi

CVLimit = 0.5

peak searching concepts17

0.0 mi

0.1 mi

0.2 mi

0.3 mi

0.4 mi

0.5 mi

0.6 mi

0.67 mi

Roadway Segment

Win # 1

Win # 2

Win # 3

Peak Searching Concepts

Note:

Window length = 0.5 mi

Expected accidents = (acc/mi)

Limiting Value = 5 acc/mi

CVLimit = 0.5

peak searching concepts18

0.0 mi

0.1 mi

0.2 mi

0.3 mi

0.4 mi

0.5 mi

0.6 mi

0.67 mi

Roadway Segment

Win # 1

Win # 2

Peak Searching Concepts

Note:

Window length = 0.6 mi

Expected accidents = (acc/mi)

Limiting Value = 5 acc/mi

CVLimit = 0.5

peak searching concepts19

Roadway Segment

0.0 mi

0.1 mi

0.2 mi

0.3 mi

0.4 mi

0.5 mi

0.6 mi

0.67 mi

Win # 1

Peak Searching Concepts

Note:

Window length = Segment length

Expected accidents = (acc/mi)

Limiting Value = 5 acc/mi

CVLimit = 0.5

sliding window concepts
Sliding Window Concepts

Site No. 1

MP 1.0

MP 2.6

1.1 mi

1.2 mi

1.3 mi

1.4 mi

1.5 mi

First Sliding Window

W = 0.3 mi

sliding window concepts21
Sliding Window Concepts

Site No. 1

Second Sliding Window

W = 0.3 mi

Sliding window is moved incrementally

by 0.1 mi along the roadway segment.

MP 1.0

MP 2.6

1.1 mi

1.2 mi

1.3 mi

1.4 mi

1.5 mi

First Sliding Window

W = 0.3 mi

slide22

X = 7.8

X = 5.6

X = 3.1

X = 4.3

X = 5.1

X = 9.8

X = 5.5

X = 6.0

X = 4.5

X = 3.5

X = 3.0

X = 4.0

X = 7.5

Site No. 23

Site No. 24

MP 35.4

MP 36.2

MP 36.7

Note:

Window length = 0.3 mi

Increment length = 0.1 mi

Expected accidents = (acc/mi)

Limiting Value = 5 acc/mi

slide23

X = 5.6

X = 7.8

X = 9.8

X = 7.5

X = 6.0

X = 5.1

X = 5.5

Site No. 23

Site No. 24

MP 35.4

MP 36.2

MP 36.7

Note:

Window length = 0.3 mi

Increment length = 0.1 mi

Expected accidents = (acc/mi)

Limiting Value = 5 acc/mi

slide24

X = 5.6

X = 7.8

X = 9.8

X = 7.5

X = 6.0

X = 5.1

X = 5.5

Site No. 23

Site No. 24

MP 35.4

MP 36.2

MP 36.7

Note:

Window length = 0.3 mi

Increment length = 0.1 mi

Expected accidents = (acc/mi)

Limiting Value = 5 acc/mi

high proportions of specific accident type
High Proportions of Specific Accident Type
  • Objective:
    • Identify sites having higher than expected proportions of specific target accidents
    • Rank sites based on difference observed proportion and expected proportion of target accident
  • Methodology
    • Calculate observed proportion (TOT only)
    • Calculate the probability that observed proportion is greater than limiting proportion (i.e., avg for site & accident type)
    • Site flagged when probability is greater than some user-specified significance level
high proportions of specific accident type cont
High Proportions of Specific Accident Type (cont.)
  • Roadway segments
    • Similar to sliding window approach
    • Longer windows are needed to reduce variance (e.g., 1.0 mi)
    • More than one window pertaining to a site can be flagged
      • Site ranked based upon maximum difference between observed proportion and expected proportion
sudden increase in mean accident frequency
Sudden Increase in Mean Accident Frequency
  • Screening for safety deterioration
    • Calculate differences in mean yearly accident frequencies
    • For the time period with the largest difference:
      • If the percentage increase is greater than a user-specified limiting value
      • Then perform test of significance
  • Based on observed accidents
  • Based on total accidents
  • Flagged sites are not rank ordered
steady increase in mean accident frequency
Steady Increase in Mean Accident Frequency
  • Screening for safety deterioration
    • Fit regression model to data of accident frequency versus year
      • If value of slope is greater than a user-specified limiting slope
      • Then perform test of significance
  • Based on observed accidents
  • Based on total accidents
  • Flagged sites are not rank ordered
screening for corridors with promise
Screening for Corridors with Promise
  • Analysis of extended corridors (e.g., 10 mi or more)
    • Roadway segments, intersections, and ramps grouped together
  • Rank order corridors based upon:
    • Accidents/mi/yr
    • Accidents/million veh-mi/yr
  • Based on observed accidents
safetyanalyst modules31
SafetyAnalyst Modules

Module 1 – Network Screening

Module 2 – Diagnosis and Countermeasure Selection

Module 3 – Economic Appraisal and Priority Ranking

Module 4 – Countermeasure Evaluation

module 2 diagnosis and countermeasure selection
Module 2 – Diagnosis and Countermeasure Selection
  • Display collision diagram (links to third-party software)
  • Identify collision patterns
  • Conduct diagnostic investigations
  • Suggest countermeasures that address identified collision patterns
  • Select appropriate countermeasures
module 3 economic appraisal and priority ranking
Module 3 – Economic Appraisal and Priority Ranking
  • Perform economic analysis of alternative countermeasures for a specific site
  • Perform economic analysis of improvements across selected sites
  • Select mix of sites and countermeasures to get maximum benefits within a specified budget
  • Develop priority ranking of alternative improvements
objective
Objective
  • Determine safety effectiveness (percent reduction in crashes) for specific implemented countermeasures
  • Conduct before-after evaluation of crash frequencies using the Empirical Bayes (EB) approach
  • Conduct before-after evaluation of shifts in crash severity or crash type proportion
why the evaluation tool
Why the Evaluation Tool?
  • The goal of SafetyAnalyst is to help highway agencies determine how funds can be spent in the most cost-effective manner to improve safety.
  • The results of Module 4 can be used to update the accident modification factors (AMFs) that are used within Module 3 for economic appraisal and priority ranking of countermeasures to be implemented at sites.
when to use the evaluation tool
When to Use the Evaluation Tool
  • A countermeasure has been implemented at a number of sites
  • The agency wants to assess how effectively the countermeasure performed:
    • Did it improve the safety performance at a site?
    • Did it reduce a specific target accident type?
what information is needed
What Information Is Needed
  • Locations of improved sites
  • Countermeasure(s) to evaluate for each site
    • Year of implementation
    • Countermeasure name(s)
  • Site characteristics
  • ADTs (before and after improvement)
  • Yearly accident counts (before and after)
  • Safety Performance Functions (SPFs)
types of analyses conducted
Types of Analyses Conducted
  • The safety effectiveness of countermeasures is quantified through the use of before-after statistical evaluations.
  • Two types of before-after evaluations can be conducted:
    • Percent change in accident frequencies, due to the implemented countermeasure, is evaluated by an Empirical Bayes (EB) technique.
    • Shift in proportion of specific collision types is evaluated using the Wilcoxon signed rank test