Data needs and limitations

1. Data needs and limitations Hossein Naraghi CE 590 Special Topics Safety February 2003 Time Spent: 8 hrs

2. 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

3. 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

4. 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

5. 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

6. 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

7. 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

8. 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

9. 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

10. 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

11. 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

12. 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

13. 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

14. 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

15. 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

16. 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)

17. 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

18. 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

19. 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

20. 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

21. 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

22. 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

23. 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

24. 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

25. 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