Chapter 8 - Crash Data Sets and Analysis

Abstract

This chapter discusses data useful for traffic safety analysis, and typical methods for analyzing such data. Two types of data are often used in traffic safety analysis: traffic safety data and supplement data. Traffic safety data can be classified into three types: police crash data, medical crash data, and safety survey data. Traffic safety data alone may not provide a correct view of the traffic safety situation and sometimes might disguise or even distort it. To understand the traffic safety situation more completely, information other than that found in the traffic safety data may be required. Understanding of how traffic safety is affected by various factors, such as geometric features of roads, traffic control types, and traffic volume, is critical for making informed decisions regarding safety improvements, and these factors are not typically found in the traffic safety data. Data analysis for traffic safety studies refers to the use of data from one or more data sources to describe a traffic safety situation and to understand factors contributing to occurrences and outcomes of crashes using numbers. Data analysis is neither simply extracting and summarizing numbers from the data nor simply creating tables and figures using the data. Data analysis is telling a story embedded in the data and is interpreting the data reliably, validly, and responsibly.