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