Table B.1 Safety Analysis Categories, Questions, Tools, and Data Needs
| Analysis Category |
Safety Analysis Question |
What tools are available? |
Data Needs |
| Benchmarking |
- How many fatalities and serious injuries are occurring in my area?
- How does this compare to other areas or my State?
|
- Descriptive Statistics
- FARS data
|
- Total crashes
- Total fatalities and serious injuries
- High-level roadway data—roadway ownership, functional classification
- Agency geographic boundary information
|
| Identify Crash Trends and Contributing Factors |
- Who is involved in crashes?
- When are the crashes occurring?
- What are the major contributing factors to crashes?
|
- Descriptive Statistics
- Trend analysis
|
- Crash severity—fatality, injury type, property damage, only
- Crash incidence data—time of day, day, month, weather, etc.
- Crash type—road departure, intersection, head-on, angle, etc.
- Contributing factors—age, impairment, seatbelt usage, speed, etc.
|
| Identify and Evaluate Focus Crash Types |
- What are the most common crash types?
- What are the most common contributing factors?
- What are the characteristics of the overrepresentation?
|
- Descriptive Statistics
- GIS Mapping
- Scatterplot
- Overrepresentation
- Risk Ratio
|
- Crash severity—fatality, injury type, property damage, only
- Crash incidence data—time of day, day, month, weather, etc.
- Crash type—road departure, intersection, head-on, angle, etc.
- Contributing factors—age, impairment, seatbelt usage, speed, etc.
|
| Network Screening—Identify Sites for Safety Improvement |
- What locations (intersections or segments) show the most potential for safety improvements?
|
- AASHTO HSM Part B Network Screening—Includes descriptive and predictive methods
- AASHTOWare Safety AnalystTM
- GIS Heat Mapping
|
- Crash severity
- Crash location
- Roadway and roadside characteristics—intersection control, number of lanes, presence and type of shoulder, presence and type of median, posted speed, horizontal and vertical alignment, etc.
- Traffic volume data—intersection total entering traffic volume, roadway segment volume per million vehicle miles
- Calibrated safety performance functions, if predictive methods are used
|
| Systemic Analysis—Identify Safety Risk Factors |
- What are the common characteristics of locations with crashes?
- What are the countermeasures to address these characteristics?
- How should we prioritize systemwide implementation?
|
- FHWA Systemic Safety Project Selection Tool
|
- Crash severity
- Crash location
- Roadway and roadside characteristics—intersection control, number of lanes, presence and type of shoulder, presence and type of median, posted speed, horizontal and vertical alignment, etc.
- Traffic volume data—intersection total entering traffic volume, roadway segment volume per million vehicle miles
|
| Corridor and Intersection Planning Safety Analysis |
- What are the safety effects of alternative roadway or intersection cross sections?
|
- AASHTO HSM Part C Predictive Method and NCHRP 17-38 Spreadsheets
- Interactive Highway Safety Design Model (IHSDM)
- Crash Modification Factors (e.g., FHWA Crash Modification Factor Clearinghouse)
- Collision Diagrams
|
- Crash severity
- Crash location
- Roadway and roadside characteristics—intersection control, number of lanes, presence and type of shoulder, presence and type of median, posted speed, horizontal and vertical alignment, etc.
- Traffic volume data—intersection total entering traffic volume, roadway segment volume per million vehicle miles
- Calibrated safety performance functions if predictive methods are used
|
