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Highway Traffic and Safety Analyses Lecture 21: Identifying Safety Deficiencies and Countermeasures Purdue University School of Civil Engineering West Lafayette Reading Assignment GUIDELINES FOR ROADWAY SAFETY IMPROVEMENTS, October 2006, link .

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Highway Traffic and Safety Analyses

Lecture 21: Identifying Safety Deficiencies and Countermeasures

Purdue University

School of Civil Engineering

West Lafayette

reading assignment
Reading Assignment

GUIDELINES FOR ROADWAY SAFETY IMPROVEMENTS, October 2006, link.

Chapter 5: SAFETY REVIEW OF HIGH CRASH LOCATIONS, Pages 27-46

identifying safety deficiencies and countermeasures
Identifying Safety Deficiencies and Countermeasures
  • Safety audits
  • Analysis of hazardous locations
    • Collision and condition diagrams
    • On-site observation
  • Crash reduction factors ?
  • Motorist feedback ?
road safety audits
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
road safety audits5
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.

road safety audits6
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.

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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?

road safety audits8
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.
road safety audit
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
analysis of hazardous locations
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
collision diagram
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.)
collision diagram http www dot state mn us trafficeng otepubl tem chap 11 2000 pdf
Collision Diagramhttp://www.dot.state.mn.us/trafficeng/otepubl/tem/Chap-11-2000.pdf
example collision diagram www city niagarafalls on ca images draft1a pdf
Example Collision Diagramwww.city.niagarafalls.on.ca/images/draft1a.pdf
on site observations
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
on site observation
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
condition diagram
Condition Diagram

A condition diagram should include:

  • Curbs
  • 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.)
crash reduction factors
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
travelers feedback
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