Data Collection and Case Analysis
The in-depth accident investigation process first requires investigators to make observations and gather information before going on to analyse the information to understand what happened and why. The methodology will therefore cover both the collection of data and case analyses. Data collection can involve a wide range of activities such as making notes, measurements, interviewing people, collecting injury details from hospitals, taking photographs and possibly making video recordings. Case analysis includes identifying and coding how and why events such as collisions between road users or injuries to road users occurred, and more specific analyses are involved, for example to calculate vehicle speeds. This document outlines the key methods investigators will need to follow to collect detailed data and photographs, and to go on to make the case analyses to reconstruct events and understand the causes of collisions and any injuries.
Teams will upload the data, photographs and analysis results into an on-line database system. Further information about the case completion process and the management of potentially sensitive data can be found in Item 12: Case Delivery.
Database Variables The database system will provide approximately 1500 variables (or fields) for data entry per case. However, it must be noted that only a sub-set of available fields will be relevant to any individual case (for example, variables defined for trucks will not be needed when there are only passenger cars involved in an accident). As an approximate guide, normally around 200 variables will need to be collected to describe the overall accident and road characteristics. In addition, around 200 to 300 variables will be completed for each vehicle involved. When it comes to the humans involved, a further around 100 to 200 variables are required. The more experienced team may need to consider entering information against further variables in order to record all observations and conclusions that have been made.
On-scene and Retrospective Working
There are two different ways of working to gather information for accident investigations: on-scene and retrospective. It is possible to investigate accidents using one or a combination of both ways of working.
On-scene work is carried out by accident investigators who arrive at the scene of the collision in time to record essential information before it is lost. On-scene working is the recommended way for teams to gather information to carry out the DaCoTA in-depth accident investigation methodology. Examples of information that an on-scene team will aim to gather quickly, include the rest position of vehicles, interviews with the road users and witnesses, light and weather conditions, and marks left on the road surface that may quickly fade. Previous work has shown the importance of arriving quickly after the incident has occurred, to gather the information required to understand what has happened and why. As a guide for the DaCoTA methodology, teams should arrive at the scene no more than 30 minutes after the time when the collision occurred. This requires teams to have a good system for being notified of accidents quickly and consistently. Depending on the size and type of road network to be covered, it may be necessary for teams to travel or work closely with their local emergency services in order to arrive in a safe and timely way. On-scene teams will, where possible, gather all necessary information during one scene visit. However it may sometimes be necessary, for practical reasons, to supplement investigations with less urgent activities on a retrospective basis. It is also recognised that less experienced or less well established teams may not be able to work on-scene.
Retrospective work includes any investigation activities carried out after the scene has been cleared of the people and vehicles involved. Examples of retrospective working include examining vehicles at a garage / recovery yard, interviewing people over the telephone or by using a postal questionnaire, and visiting the road location hours or days after the collision occurred. Retrospective work can be a more practical way to gather evidence that is not likely to move or change over time, and there are experienced and successful research projects that use only retrospective methods. Additionally, this method is a valuable way to supplement on-scene activities. It is also recognised that less experienced or less well established teams may only be able to work retrospectively.