CE 552 Week 13

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CE 552 Week 13

• Identifying problems and solutions The safety
  audit (materials, chapter 9)
• Responses/countermeasures/Crash reduction
  factors/AMFs (materials, chapter 10)

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• Improve safety
• Interdisciplinary teams
• Existing or new roadway
• Planning
• Construction
• Design
• ID problem elements
• ID opportunities

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• Team quals
• Crash investigation
• Traffic engineering
• Road design
• Enforcement
• Maintenance
• EMS
• Human factors
• Background info
• Plans, volumes, crash data

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Development of countermeasures
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Principles of countermeasure development

• The process of countermeasure development should
  aim to
• Determine a Range of measures likely to influence
  the dominant crash types and road features
• Select countermeasures based on professional
  judgment and experience that can expected to
  reduce the number or severity of dominant crashes

From Ogden, Chapter 7
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Principles of countermeasure development
(continued)

• Check to see if adopted countermeasures have any
  undesirable consequences in
• Safety terms
• e. g. lead to an increase in number or severity
  of another crash type
• Traffic efficiency
• Environmental terms
• Be cost-effective
• Maximize the benefits from HRL program
• Be efficient
• Produce benefits which outweigh costs

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Principles of countermeasure development
(continued)

• A safe road is one that recognizes the realities
  and limitations of human decision making
• The management of road safety must ensure the
  road environment not place demands upon the
  driver that are beyond the drivers ability to
  manage, or which are outside normal road user
  expectations
• What are the characteristics of a safe road?

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Characteristics of a safe road

• A safe road is defined as one which is designed
  and managed so that it
• Warns the driver of unusual features
• Informs the driver of conditions to be
  encountered
• Guide the driver through unusual sections
• Control the drivers passage through conflict
  points and road links
• Forgives a drivers inappropriate behavior

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Intersections

• The main design principles for intersections are
• Minimize the number of conflict points and thus
  the opportunity for crashes
• T-intersections and roundabouts have fewer
  conflict points than 4-way intersections
• Give precedence to major movements through
• Alignment
• Delineation
• Traffic control
• Separate conflicts in space or time

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Intersections (continued)

• Control the angle of conflict
• Crossing streams of traffic should intersect at a
  right angle or close to it
• Merging streams should intersect at small angles
  to ensure low relative speed
• Define and minimize conflict areas
• Define vehicle paths
• Ensure adequate sight distances
• Control approach speed using
• Alignment
• Lane width
• Traffic control
• Speed limits

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Intersections (continued)

• Provide clear indications of right-of-way
  requirements
• Minimize roadside hazards
• Provide access to use intersection for
• Vehicular traffic
• Special provisions for heavy vehicle and public
  transportation vehicles
• Non-vehicular traffic
• Pedestrians and other vulnerable road users
• Simplify the driving task
• Minimize road user delay
• Roundabouts usually include to some degree all
• of the above principles

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Mid-block locations

• The principles for design and operation of
  non-intersection locations include
• Consistent standards of horizontal and vertical
  alignments
• Develop roadway cross sections to suit road
  function and traffic volumes
• Delineate roadway and vehicle paths
• Standards of access control from abutting land
  use
• Ensure that roadside environment is clear or
  forgiving

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Mid-block locations (continued)

• Overlaying all of the above principles is a vital
  need to consider particular needs of all road
  user groups
• Careful consideration of these needs will ensure
  the quality of final treatment
• Pedestrians have special needs that should be
  separately considered when investigating safety
  problems and developing countermeasures
• Special requirements of heavy vehicles
• Negotiating low-radius turn
• Traveling through horizontal curves with adverse
  super-elevation
• Other user groups needs

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Countermeasure selection

• Matching solutions to problems
• The key to selection of countermeasures is to
  concentrate on the particular crash types which
  identified in diagnosis phase
• The final choice will be based upon judgment and
  experience
• Utilizing countermeasures which have been
  successful in similar situations elsewhere

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Criteria for countermeasure development

• There are number of criteria for countermeasure
  selection
• Technical feasibility
• Can countermeasure provide an answer?
• Does it have technical basis for success?
• Economic efficiency
• Is countermeasure likely to be cost effective?
• Will it produce benefits to outweigh its costs?
• Affordability
• Can it be accommodated through program budget?
• Should a cheaper solution be adopted?

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Criteria for countermeasure development
(continued)

• Acceptability
• Does the countermeasure target the problem?
• Will it easily understandable by community?
• Practicality
• Is there likely to be a problem of
  non-compliance?
• Can the measure work without unreasonable
  enforcement effort?
• Political and institutional acceptability
• Is the countermeasure likely to attract political
  support?
• Will that be supported by the organization
  responsible for its installation and on-going
  management?

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Criteria for countermeasure development
(continued)

• Legal compatibility
• Is the countermeasure a legal device?
• Will users breaking any law by using it in the
  way intended?
• Compatibility
• Is the countermeasures compatible with other
  strategies which have been applied in similar
  situations?
• It can be seen that adapting countermeasures to
  particular problem is a complex process.
• Development of countermeasures requires
  understandable technical and institutional
  framework to provide the guideline principles and
  motivation for action

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From Garber
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From Khisty
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1990 NHTSA/FHWA effective safety measures
Whats new since then that you know about?
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Crash Reduction Factors

• Aka Accident Modification Factors or Functions

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Do you know another way to do this? See
combining crash reduction factors
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Access Control
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Alignment

• Curved sections have 1.5-4.0 times the crash rate
  of tangent sections

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Cross sections
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Intersections
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Pedestrians
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Crash Reduction Factors for CountermeasuresIssue
Briefs and Desktop Reference
Maurice Masliah, Ph.D. Senior Researcher iTRANS
Consulting [phone] ext 5295
mmasliah_at_itransconsulting.com
Prepared by iTRANS Consulting
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Updated Issue Briefs
Intersections
Traffic Signals
April 2004
September 2007
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New Issue Briefs
Pedestrian
Roadway Departure
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New Product Desktop Reference
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What is a CRF?

• Crash Reduction Factor

• Percentage crash reduction that might be expected
  after implementing a countermeasure
• CRF of 25 means a 25 reduction in crashes
• CRF of -20 means a 20 increase in crashes

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Issue Briefs Purpose

• One CRF for each countermeasure
• The best available CRF
• (accuracy and precision checks)
• Additional information relevant to the CRF
• (traffic control, area type, etc.)

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Desktop Reference Purpose

• Multiple CRFs for the same countermeasure (where
  available)
• CRF functions
• Additional information such as study type, number
  of observations, CRF range (high - low)

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Product PurposeIowa DOT

• Tom Welch
• State Transportation Safety Engineer
• Iowa Dept of Transportation

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Roadway Departure Issue Brief

• Purpose
• CRFs
• How to Use

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Roadway Departure CRF Example

• CRF 38(10)17

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CRF Example
Expected crashes without treatment
Expected crashes with treatment
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CRF Example

• CRF 38(10)17
• Bold type means a rigorous methodology was used
  to estimate the CRF, and the standard error is
  relatively small
• (10 ) is the standard error for this CRF
• 17 is the reference number
• details at the end of the Issue Brief

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CRF Confidence Interval

• Estimation of confidence interval 38(10)17
• ? 2 standard errors from the CRF
• 18 (38 - 2 X 10) and 58 (38 2 X 10)
• Expected safety effect of the countermeasure
  between 18 and 58

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Example ApplicationDouglas County

• Keary B. Lord
• Assistant Director/
• Traffic Operations Division Manager

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Accuracy

• Accuracy is the proximity of the estimate of the
  CRF to the true value
• Two types of bias affect accuracy
• 1. Regression to the mean bias
• 2. Traffic volume bias

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Precision

• Precision is the degree to which repeated
  estimates of the CRF are similar to each other
• Measure of precision standard error of CRF

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Reliability

• Reliability is defined here as the combination of
  precision and accuracy
• CRFs that pass the reliability test are shown in
  bold font

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Reliability Selection Criteria and Thresholds
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Number of CRFs and Bold CRFs

• Very few published CRFs are considered
  reliable!

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CRF Proper Use and Limitations Colorado DOT

• TBD Bryan Allery/Jake Kononov
• Colorado Dept of Transportation

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Highway Safety Improvement Program (HSIP)

• Implementation

• Planning

• Evaluation

(3) A comparison of accident numbers, rates, and
severity observed after the implementation of a
highway safety improvement project with the
accident numbers, rates, and severity expected if
the improvement had not been made.
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HSIP CRFs

• Evaluation legislation specifies the information
  needed to produce CRFs
• Our review of HSIPs has not found any states
  which tie their evaluation work with CRF
  generation
• Potential to link tasks currently being conducted
  with improving knowledge of effectiveness of
  countermeasures

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Strategic Highway Safety Plan (SHSP)

• CRFs should be part of the process of selecting
  countermeasures
• Intersections as an emphasis area within a SHSP
• Task team identifies left-turn crashes at
  intersections as an overrepresented crash type
• What are appropriate countermeasures?

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Strategic Highway Safety Plan (SHSP)

• Review of Intersection Issue Brief for left-turn
  crash CRFs
• Provide protected left turn phase 16(2)19
• Install left-turn lane (physical channelization)
  249
• Install cameras to detect red-light running
  45(6)27
• Identify intersection locations and conduct a
  cost-benefit analysis

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Future Direction Whats Next?

• Accident Modification Factors and Functions
  (rather than CRFs)
• Increase in number of studies that evaluate
  safety effects of countermeasures
• More stringent criteria in adoption of AMFs
• New tools

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What is an AMF?

• Accident Modification Factor

• Multiplier representing the expected change in
  crashes
• CRF of 25 equals an AMF of 0.75
• CRF of -20 equals an AMF of 1.20

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Accident Modification Functions

• Today, CRFs / AMFs for most countermeasures are
  noted as constants
• However, CRFs / AMFs are really functions of
  environmental variables
• Traffic volume
• Traffic mix (trucks, pedestrians, bicyclists)
• Road geometry
• Operational conditions

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More Stringent Inclusion Criteria

• Highway Safety Manual inclusion process
• Accuracy and precision of AMFs
• Standard error of 0.1 or less indicates AMF that
  is sufficiently accurate, precise, and stable
• Companion AMFs with standard errors of 0.2 - 0.3
  are also included
• indicating the potential safety effects of the
  treatment on other facilities, or other crash
  types and severities

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Future Direction

• Periodical Update of Issue Briefs and Desktop
  Reference
• Search new information
• current research projects http//rip.trb.org/
• government-funded documents published
  http//www.ntis.gov/search/index.asp?
• bibliographic database http//ntlsearch.bts.gov/tr
  is/index.do

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New Tools and New AMFs

• Low Cost Safety Improvements Pooled Funds Study
• Highway Safety Manual (HSM)
• SafetyAnalyst
• Interactive Highway Safety Design Model (IHSDM)

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Many more like this in the reference