data needs and limitations hossein naraghi ce 590 special topics safety february 2003 time spent: 8...
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Data needs and limitations
Hossein NaraghiCE 590 Special Topics
SafetyFebruary 2003
Time Spent: 8 hrs
Data needs and limitations
Availability of reliable data is the main factor for scientific analysis of crash data
For the purpose of scientific analysis of crash data and development of countermeasures
• What data are needed• How data generated• Crash database management
Information requirements Collection and interpretation of
accurate and comprehensive data enable road safety management Better understanding of operational
problems Accurate diagnosis of crash problems Develop remedial measures Evaluate the effectiveness of road
safety programs
Information requirements Although the need for data is universally
recognized, there is little consistency in collected data Comparative study of eleven European
countries found that• Only two variables (date & hour) were collected in
all eleven countries• 7 percent of items were recorded in three countries• 70 percent recorded in only one country
There is no nationwide crash data reporting system in US
• Little consistency within states for recorded data elements
Information requirements There are significant variation in data,
even in the field of safety engineering, which analysts find useful in analysis of crashes One particular inconsistency is use of
information relating to accident type UK claims that their system is adequate
without it! Some UK local authorities who use detailed
accident type data, claim that it is a vital tool to their crash investigation process
Information requirements We are in early stage of professional
development of road safety engineering in general and crash investigation in particular
More comparative research between different countries is necessary to determine What data are really needed What tools are most effective What data management and analysis process are
efficient What countermeasures are most cost-effective
Users and use of information There are many potential users of crash
data, and their needs are not identical and in many cases in conflict Road safety engineers
• Develop remedial measures Police
• Charging a person at fault in crash• Enforcement activities
• Location of speed cameras• Breath testing stations
Users and use of information (continue) Insurers
• Seeking facts before settling claims Lawyers
• Compensation for injuries Road safety educators
• To ensure that their efforts well targeted Safety administrators
• Report statistical information on road crashes Researchers
• Access good reliable database Vehicle manufacturers
• Assess the safety of their products
Information requirements
To develop an effective road safety management system, information needed not only on road crashes, but on other pertinent factors as well A suggested integrated database include
• A crash file• Time, environment and circumstances of crash
• A driver file• Personal identification, license type and status, violations,
crashes and safety education
• A vehicle file• Type and vehicle inspection
Information requirements (continued)
• A roadway file• Road characteristics, classification, traffic volumes, etc
• A commercial vehicle file• Configuration, body type, hazardous materials and
operator
• A citation/conviction file• Identifies violation, violator and adjudication action
and results
• An emergency medical service file• Information about emergency care and victim
outcome
• Provisions for file linkages
Crash data capture Crash Data
Crash location Crash time Who was involved
• People, vehicles, animals and roadside objects Result of the crash
• Fatal, injury, PDO Environmental condition How did crash occur
Crash data capture (continued) Police crash report
Source of the most crash databases is a police report form
Technology New technologies for data capture are as
follow:• GPS• GIS• scannable crash report forms and laptop computers
in police cars
Crash data elements In general three types of data are required for the
purpose of hazardous road location investigation Crash data Road data Traffic data
• Traffic volume• Daily, hourly, seasonal
• Composition• Cars, trucks, buses, motorcycles, bicycles
• Pedestrians• Volume, age group represented
• Vehicle speed• Mean, 85 percentile
• Parking type• Yes/no, type
Crash data coding Crash data obtained from police crash
report forms is coded for the purpose of efficient computer storage and retrieval
Data coder has to use information to determine four very important pieces of information Location of crash Whether occurred at intersection Accident type Crash severity
location Precise knowledge of the location of the crash
is one of the key pieces of information required by the road safety engineers
The coders task is to translate that information onto a referencing system
There are two basic options A coded road network
• Where each node intersection is numbered• Accident at nodes are coded according to the relevant node
number, while those between nodes are coded with reference to the adjacent nodes
A grid reference system, based upon a national geographic grid
Crash severity and casualty class
Severity is important because it often use to rank crashes
Crash severity and casualty class is an important area, but there is often a degree of subjectivity
In most US states, the five point scale often referred to as KABCO K person with fatal injury A person with incapacitating injury B person with non-incapacitating evident injury C person with possible injury O no injury (property damage only)
Crash severity and casualty class (continued)
A fatal crash is defined as one in which death occurs within a given period of time as a result of injuries sustained in the crash
Suicides are generally excluded A coroner may determine that a person in
the crash died before the crash occurred Through a heart attack
• Crash would not be coded as fatal since it was not the cause of death
Crash database management
Prime characteristics of a crash database management system Competent crash reports
• Supported by training and supervision A report form adopted to user’s need Attention to detail in the preparation of reports Accurate data entry and processing Free-flowing output to interested parties Feedback of user comments to induce system
improvements
Crash database management (continued)
Database can be used to produce routine periodic reports such as Lists of crash by locations
• Monitor to detect emerging problem sites Lists of high crash locations
• Monitor to develop priorities for treatment Detailed summaries of crashes that occurred at
high crash locations• Use to prepare collision diagram
Detailed summaries of variables coded from the crash report forms
Crash database management (continued)
• Accident type, vehicle type, time of day, alcohol related, pedestrians crashes, etc. use for countermeasure developments
Summaries of crash types susceptible to enforcement
• Speeding, alcohol related, use by police in planning enforcement strategies
Summary reports• Preparation of official statistics
Summaries of crashes involving particular hazardous features
• Roadside objects, railway crossing, useful for planning proactive or preventive programs
Supplementary data sources
While police crash report is the basic source of crash data, there are some other sources which may be useful and applicable in certain circumstances Local knowledge
• Local government staff• Emergency service personnel• Local safety groups• Local businesses
Interview of road users• People involved in a crash at a site of interest, which are source
of useful information for traffic officials in development of countermeasures
In-depth studies of particular group of crashes• Single vehicle fatal crashes, to gain better understanding of the
nature of those crashes
Supplementary data sources (continued)
Traffic conflict surveys • May be used when the collection of crash data is not
practical or period of evaluation is too short to collect sufficient samples
• Field observation• Video recording of conflicts
• Information gained in this way is valuable in • getting a sound understanding of the traffic operation• Find interactions between traffic streams at the site
• As a proxy measure of safety• Assumption must be made about relationship between proxy
measure (conflict) and crash rates
Site investigations are necessary component of a countermeasure development program
Data limitations Systematic reporting bias
Database not truly reflective of crash situation Random bias
Under-reporting can result in distorted picture of road crash situation
• Numerically• Nature of the crashes• Not recording particular factor, means it was not
present• Factor was present, but police officer did not think
that it is not important
Data limitations (continued) Coding errors Location errors Discontinuities
Data from one time period can not be compared to another time period
Delays Takes too long to have data available for
analysis, so countermeasures development is responding to historical crashes which may be out of date
Data limitations (continued) Hidden problems
It is assumed that database is good indicator of road safety problems
There might some masked problems• Pedestrians avoid using an area because perceived
safety problem This kind of problems need to be tackled
through a road safety audit or identified through community consultation
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