1. School of Civil Engineering
Highway Traffic and Safety Analyses
Lecture 21: Identifying Safety Deficiencies and Countermeasures
Purdue University
School of Civil Engineering
West Lafayette

2. Reading Assignment
GUIDELINES FOR ROADWAY SAFETY IMPROVEMENTS, October 2006, link.
Chapter 5: SAFETY REVIEW OF HIGH CRASH LOCATIONS, Pages 27-46

3. Identifying Safety Deficiencies and Countermeasures
Safety audits
Analysis of hazardous locations
Collision and condition diagrams
On-site observation
Crash reduction factors ?
Motorist feedback ?

4. Road Safety Audits What is Road Safety Audit?
Formal examination of an existing or future road or traffic project by an independent team of trained specialists to identify road safety deficiencies.
Summary of the ITE report on RSA

5. Stages of safety audits = Stages of a road project
Road Safety Audits
Stages of safety audits = Stages of a road project
Feasibility Study -- scope of a project, route choice, selection of design standard, impact on the existing road network, route continuity, provision of interchanges or intersections, access control, number of lanes, route terminals, stage development, and more.
Preliminary Design -- horizontal and vertical alignment, sightlines, intersection layouts, land and shoulder width, pavement side slope and superelevation, overtaking lanes, provision for parked and stationary vehicles, provision for cyclists and pedestrians, effects of departures from standards and guidelines, safety during construction.

6. Road Safety Audits
Detailed Design -- line markings, signing, delineation, lighting, intersection details, clearances to roadside objects, provision for road user groups with special requirements (for instance, pedestrians, cyclists, people with disabilities, trucks and buses), temporary traffic management and control during construction, drainage, poles and other roadside objects, landscaping, slopes and guard fencing.
Pre-opening -- the audit team would walk or drive through a project to check on the quality of completed safety features. They would inspect many of the same items as were considered during the design process, and they would try to be at the project during different conditions--day and night, wet and dry, etc.
In-service -- identifies weaknesses in the functioning of safety features while the road is open to motorists.

7. Example Road Safety Audit Form
N/A
Yes No
Comments
STAGE 2: DRAFT DESIGN
2.2 DESIGN ISSUES (GENERAL)
1 Geometry of Horizontal and Vertical Alignment
1A Does the horizontal and vertical design combination of the road provide a suitable alignment for drivers?
1B Do the combinations of horizontal and vertical design elements conform to design practice? (i.e. there shouldn’t be undesirable combinations of horizontal and vertical design)
1C Is the design free of cues that would cause a driver to misread the road characteristics? (e.g. visual illusions, confusing delineation of lines of trees, poles, etc.)
1D Does the alignment selected ensure speed consistency?
1E Are overtaking / climbing criteria met?
2 Typical Cross Sections
2A Are the lane widths, shoulders, medians and other cross section features in accordance with standard design and adequate for the function of the road?
2B Is the width of traffic lanes and roadway suitable in relation to:
- alignment? - traffic? - vehicle dimensions? - speed environment? - combinations of speed and traffic volume?

8. Road Safety Audits Process
The audit team should include specialists of highway safety engineering.
The findings and audit advice should be documented and formally reported.
The reasons for rejecting any element of advice should be explained.
Provisions for arbitration should be made.
Independence of audit must be maintained, and there should be an awareness of possible litigation if there are subsequent failures.

9. Road Safety Audit RSA tends to improve nominal safety
RSA improves objective safety only if the design and traffic control standards are correct and experts are right
Highway administration accepts RSA if RSA is believed to reduce the risk of litigation

10. Analysis of Hazardous Locations
Prepare a collision diagram
Identify predominant crash patterns
Visit the site
Prepare a condition diagram
Look for safety deficiencies
Propose countermeasures
Sight distance, volume, speed, and other studies may be needed

11. Collision Diagram A collision diagram includes:
Drawing of intersection
Identification of diagram
Identification of streets
and crash information:
Direction of travel
Date of accident
Time
Road conditions
Weather conditions
Any unusual conditions (flood, storm, intoxication, etc.)

12. Collision Diagram

13. Collision Diagram http://www. dot. state. mn

14. Example Collision Diagram www. city. niagarafalls. on
Example Collision Diagram

15. On-site Observations
Seeing the road from drivers’ perspective can be revealing
Watching traffic can be revealing (traffic conflicts, traffic violations, erratic behavior)
A manual of road safety audits can be useful

16. On-site Observation
Visit during conditions with the high crash frequency (rush hour, night, winter?)
Make a condition diagram
Drive the road
Walk the road
Watch the traffic
Videotape from the drivers’ position (in motion)
Videotape from the raised elevation (stationary camera)
Make still pictures of the road for documentation
Make report, drawings, audio recording
Look for design and traffic control deficiencies

17. Condition Diagram A condition diagram should include: Curbs Bridges
Roadway limits
Property lines
Sidewalks
Driveways
View obstructions on corners
Physical obstructions on roadway
Ditches
Bridges
Traffic signals
Signs
Pavement marking
Streetlights
Grades
Road surface
Type of adjacent property
Irregularities (potholes, dips, etc.)

18. Condition Diagram

19. On-Site Observation Report

20. Location Analysis Form

21. Crash Reduction Factors ?
Crash reduction factors give the expected percent reduction of crashes after a specific improvement
Do not use crash reduction factors to get an idea of safety improvements
Most of the crash reduction factors have been derived after a particular road deficiency has been corrected
They may overstate the safety effect if a road or control change is not needed

22. Travelers’ Feedback ? People’s complaints represent subjective safety
They impact decisions about safety projects (political pressure)
They may include valuable information about road safety deficiencies
The link between subjective safety and objective safety is not fully understood
Caution should be exercised