Data needs and limitations Hossein Naraghi CE 590 Special Topics Safety February 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