Safety Impacts of Pavement Edge Dropoffs

1
Safety Impacts of Pavement Edge Drop-offs
2
AAA Foundation for Traffic Safety

• Established in 1947
• 501 (c)(3) Not-For-Profit
• Research affiliate of AAA/CAA
• North American Focus

3
Mission

• Identify traffic safety problems
• Foster research that seeks solutions
• Disseminate information and educational materials

4
Funded through the generosity of and its
members
5
Published September 2006 Prepared by Iowa State
University Center for Transportation Research
Education and Midwest Research Institute Availab
le online at www.aaafoundation.org
6
Project Advisory Panel

• Technical Experts and key stakeholders from
• State DOTs
• Federal Highway Administration
• University Transportation Researchers
• Insurance Institute for Highway Safety
• AAA
• Other transportation safety researchers and
  advocates

7
What is Pavement Edge Drop-off?

• Difference in height between paved road surface
  and shoulder or adjacent surface
• Caused by
• Inadequate maintenance
• Erosion
• Broken pavement
• Resurfacing road but not shoulder

8
The Problem

• If a vehicle leaves the road, edge drop-off makes
  it difficult to drive back on, increases crash
  risk
• Crashes related to pavement edge drop-off are a
  major source of tort liability claims filed
  against highway agencies
• Need research-based guidance to prevent drop-off
  and crashes

9
Purpose of Study

• To evaluate current highway agency guidelines and
  practices for monitoring and addressing pavement
  edge drop-off
• To assess the prevalence and depth of drop-offs
• To investigate frequency and severity of
  drop-off-related crashes
• To develop recommendations for reducing drop-off
  and decreasing risk to drivers

10
The Study

• Comprehensive review of published guidance for
  road construction and maintenance
• Survey of state guidelines and practices for
  identifying and addressing drop-off
• Measurement of drop-off on paved rural roads with
  unpaved shoulders in 2 states
• Inspection of Police Accident Reports for crashes
  possibly related to drop-off
• Statistical analysis of crash rates and drop-off
  presence in 2 states
• Review of driver education and training materials

11
Review of Existing Guidance

• Findings
• There is no national standard for drop-off
  prevention or mitigation
• There is not agreement on what drop-off depth and
  shape is dangerous
• Existing guidance is not based on crash data
• Wide variation in maintenance practices

12
Survey of States and Provinces

• Surveyed 14 U.S. states and 2 Canadian provinces,
  finding
• Shoulder paving and width varies by state and
  road type
• Most provide signage and/or barricades if there
  is drop-off during construction
• Most sample drop-off regularly
• Max acceptable drop-off varies from 1.5 to 3.0
  inches

13
Frequency and Depth of Drop-off

• Measured drop-off along sample of 2 mile
  segments of 2-lane paved rural roads in 2 states

14
Frequency and Depth of Drop-off

• Findings
• 0.1 of drop-off measurements 5.0 inches deep
• 4.0 inches
• 1-3 of drop-off 3.0 inches
• 12-19 of drop-off 2.0 inches
• Note that both states consider 2-inch drop-off
  unacceptable

15
Drop-off Related Crashes

• Examined sample of Police Accident Reports from 4
  states for evidence that drop-off contributed to
  the crash
• Restricted to crashes on paved rural roads with
  unpaved shoulders
• Methodology developed for related Federal Highway
  Administration study
• Analyzed sequence of events, narrative, and
  diagram of crash
• Separate regression analysis of crash density and
  drop-off prevalence on segments where drop-off
  was measured

16
Drop-off Related Crashes

• Findings
• Drop-off may contribute to approximately 2 of
  crashes on paved rural roads with unpaved
  shoulders
• Crashes possibly related to drop-off are more
  severe than other crashes on similar roads more
  than twice as likely to be fatal
• Density of crashes on segments increases with
  drop-off prevalence

17
Review of Driver Training Materials

• Reviewed state drivers manuals and driver
  education textbooks
• Project panel developed recommended educational
  message to instruct motorists on returning to the
  road safely after driving over a drop-off
• AAA Foundation used panel recommendation to
  develop Over the Edge and Back educational
  brochure

18
Project Panel Recommendations

• State and local transportation agencies should
  provide training to maintenance and construction
  staff
• Agencies should require routine inspection of
  shoulder conditions and prompt remediation of any
  pavement edge drop-off over a certain threshold
  depth
• Threshold depth should be 2.0 inches at most

19
Project Panel Recommendations

• Agencies should adopt paved shoulder policy
  requiring paved shoulders with minimum width of 2
  feet, or wider if conditions warrant
• Agencies should include a 30 35 beveled edge
  (e.g., FHWA Safety Edge) on all roadway
  resurfacing projects

20
Project Panel Recommendations

• States should analyze crash data to assess
  contribution of drop-off to crashes on their
  roads
• Data improvement may be necessary in some states
• More research is needed on motorist understanding
  of roadway-condition related signage
• State driver manuals should include advice on
  hazards of drop-off and techniques for safely
  re-entering the road

21

• For more information,
• please go to
• www.aaafoundation.org

22
The AAA Foundation for Traffic Safety is a
501(c)(3) public charity located in Washington,
DC that is dedicated to saving lives and reducing
injuries. It is supported by donations from
AAA/CAA Clubs, AAA/CAA members, and other
organizations associated with AAA/CAA.