Today, various measures are used to estimate the severity of a traffic conflict. However, these measures are all limited to estimating the crash risk and do not include any estimates of the possible consequences of a potential crash. In accident analysis the estimated severity of the event is related to the outcome of the crash, such as injury levels. This article proposes a new method for estimating the severity of safety critical events based on both an estimate of crash risk and an estimate of possible consequence that, in addition to a measure of safety margins, takes vehicle mass as well as the relative speed of the involved road users into consideration. The article compares the estimated severity of 61 conflicts and 9 accidents of the proposed method with the traffic conflict technique.

The results from the severity estimates of our proposed method show a significant difference in the severity levels of events involving vehicles with similar mass compared to critical events involving vehicles with dissimilar mass and events involving pedestrians. The proposed method gives the possibility to compare different conflicts, with regard to severity, with each other regardless of what type of conflict it is, e.g. intersection or rural road, or what kind of road users that are involved.

In addition, an event classification, i.e. serious or very serious event, based on the severity estimate of the proposed method, shows promising results indicating that the severities are estimated in a homogenous way. The article concludes that our proposed method of estimating the severity of critical event seems to be able to reflect the dangerousness in a more realistic way than the traffic conflict technique and should facilitate the development of traffic safety analysis methods.

This study uses continuously logged driving data from 166 private cars to derive the level of jerks caused by the drivers during everyday driving. The number of critical jerks found in the data is analysed and compared with the self-reported accident involvement of the drivers. The results show that the expected number of accidents for a driver increases with the number of critical jerks caused by the driver. Jerk analyses make it possible to identify safety critical driving behaviour or “accident prone” drivers. They also facilitate the development of safety measures such as active safety systems or advanced driver assistance systems, ADAS, which could be adapted for specific groups of drivers or specific risky driving behaviour.

Naturalistic driving studies permit the study of driving behaviour during every day driving. Such studies have a long duration and rare events such as near-crashes and even crashes do occur during the period of the study. This fact gives an opportunity to study events that are otherwise difficult to find. However, the vast amount of data recorded within these naturalistic driving studies demands a huge amount of manual work to identify hazardous situations. This paper concerns the development and validation of a new method, based on critical jerk, to identify safety critical braking events during car driving. The method was compared with one of today's most used method, which is based on the longitudinal acceleration measure. Both methods were applied on near-crash data from the 100-car naturalistic driving study previously carried out by the Virginia Tech Transportation Institute (VTTI). The data included 637 near-crashes. The results from the analyses showed that the critical jerk method performed approximately 1.6 times higher overall success rate than the method based on the longitudinal acceleration measure. In addition, a positive correlation was found between driver's safety critical braking event and crash involvement. The conclusion is that the critical jerk method is capable of detecting safety critical braking events and may also be used for assessing high risk drivers.

A new method for detecting jerks in safety critical events, based on the characteristics of the braking caused by the driver in time critical situations, has been developed and evaluated in a small pilot test and also applied on a naturalistic driving study. A portable event data recorder, capable of measuring and recording acceleration profiles for a predetermined time period before and after the safety critical situation, has also been developed to ensure high data quality used to evaluate the proposed method. Thus, an analysis of the acceleration profile is possible during the entire braking event. The study involves analyses of acceleration profiles and different characteristics of the rate of change of the acceleration profiles, i.e. jerks, such as negative jerk, used in previous studies, and a peak-to-peak value of the jerk. The finding is that the proposed method provides a more distinct difference between critical and potentially critical events and thus may be an appropriate method used to detect safety critical events.