ltc, jack r. widmeyer transportation research conference, 11/04/2011, wen cheng
TRANSCRIPT
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A New Method to Identify Hot Spots in roadway Network
BYWen Cheng, Ph.D., PE Assistant Professor
Civil Engineering DepartmentCal Poly Pomona
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Presentation Outline• Hotspot Identification (HSID) background• Description of the new proposed HSID
method• Application of the new method• Summary and Conclusions
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Crashes in Real Life: Huge Burden
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Crashes in the U.S.• 42,116 fatalities (i.e., 115 persons
killed/day)• 1.51 fatalities/100M VMT• 14.79 fatalities/100K Population• 231 Billion Economic Cost• 41% alcohol-related fatalities• 29.7% Speed-related fatal crashes
Source: 2005 NHTSA
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Crashes in California
Source: 2005 CA Statistical Abstract
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How to address safety challenges• ISTEA legislation (1991) and TEA-21(1998)
required each state develop safety management systems.
• SAFETEA-LU (2005) establishes a new core Highway Safety Improvement Program– structured and funded to make significant
progress in reducing highway fatalities
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Safety Management System Basic Components
1• Identification of hot spots
2• Diagnosis of crash problems
3• Selection of countermeasures
4• Evaluation of countermeasures
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Current Practice of HSID • Rank a set of candidate locations in terms
of the registered accident counts or expected long-term accident counts
• General assumptions– accident process can be viewed as a
sequence of Bernoulli trials –Accident counts of the set of locations follow
negative binomial distribution
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State-of-the-art HSID Method: Bayesian
)(
)|()()|(
Kf
kKfkfKkf
Where:
f (k)= prior pdf of k’s of reference population (similar sites ), it follows gamma distribution whose parameters are obtained based on empirical data.
f (K|k)= pdf of accident counts on a specific site whose expected safety is k, it is Poisson distribution.
f (K)= pdf of a group of collected accident counts.
f ( k|K)= posterior pdf of λ of the site which has x counts.
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General Process of Diagnosis
1• Identification of dominant accident types of hot
spots
2• Data amplification by detailed on-site
investigation (maybe include conflict studies)
3• Identification of dominant factors and/or road
features
4• Determine the nature of the accident problem
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General Process of Countermeasure Selection
1• Determine the range of measures likely to influence the
dominant accident types and road features
2• Select countermeasures expected to reduce the number and
severity of accidents of the type dominant at the location
3
• Check that adopted countermeasures do not have undesirable consequences, either in safety terms or in traffic efficiency terms
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Problems of Current Safety Practice• The safety management components are
somewhat isolated• Much less safety resources are allocated to
the first step: HSID• Much more resources are invested in the
subsequent steps.• Result: the substantial resources invested in the
subsequent steps could be wasted on the sites that are wrongly identified in the first step
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The New HSID Method Proposed• Streamline the safety improvement process by
incorporating the crash type and crash severity into HSID step.
• Crash type recognition: facilitate the crash diagnosis process.
• Crash Severity recognition: facilitate the economic evaluation of countermeasure alternatives.
• All information is incorporated under Bayesian framework.
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Case Study: City of Corona• Crossroads Collision Database software• 298 Intersections: 141 signalized and 157
non-signalized • Crash period: 10 years (2000~2009). • A set of roadway factors: minor ADT, major
ADT, speed limit, etc.
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Method Evaluation• Crash data divided into 2 groups: Before period
(2000~2004), After (2005~2009)• Use top 10% locations as crash hotspots• Evaluation criteria: overall crash costs of future
period for all crashes and crash types.• Results: type-and-severity recognition method
shows advantages over the typical one in terms of both criteria.
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Discussion on Future Direction• Crash data from other cities or counties are
needed.• Data sample size (298) is relatively small.• Special statistical modeling techniques are
required to address issues associated with crash type and severity.