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Bagdadi O.,Swedish Road and Transport Research Institute
Accident Analysis and Prevention | Year: 2013

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. © 2012 Elsevier Ltd.

Abate M.,Swedish Road and Transport Research Institute
Journal of Transport Economics and Policy | Year: 2014

Recent performance indicators in the European road freight transport sector show there is an excess capacity. To shed light on this, this paper studies two aspects of capacity utilisation in trucking: the extent of empty running and the load factor. Using a joint econometric modelling framework, the paper shows that they can be explained as a function of haul, carrier, and truck characteristics. For estimation, a unique dataset from the Danish heavy vehicle trip diary was used. The results indicate distance and being a for-hire carrier have a positive effect on capacity utilisation, whereas the effect of truck size is non-linear.

Forward S.E.,Swedish Road and Transport Research Institute
Transportation Research Part F: Traffic Psychology and Behaviour | Year: 2010

To disregard the speed limit is the most frequently reported violation. High speed has been related to road traffic accidents and is the main reason for people being killed or seriously injured. There is evidence to suggest that speeding is related to beliefs which minimize the perception of risk. The aim of the following study was therefore to determine what motivates drivers to speed. An extended version of the Theory of Planned Behaviour was used to examine the role of attitudes, subjective norms, perceived behavioural control and descriptive norms. The participants were randomly selected from the general public. The results demonstrated the value of TPB in the prediction of speeding on a rural road and that positive beliefs had a stronger link to intention than negative ones. It was also able to demonstrate the significant effect of descriptive norm and distinguish between two different groups of intenders; one low in ambivalence and one high. The latter group is relatively unknown and future research is required to explore their needs and motives in some more depth. Finally, the role of gender was assessed and the results showed that driving experience and age were important factors explaining women's lower intention to violate. Furthermore, the model was able to predict male and female intentions equally well and the unique effect of the various constructs within the TPB was also very similar. The findings from this study call for more tailored interventions. © 2010 Elsevier Ltd. All rights reserved.

Janhall S.,Swedish Road and Transport Research Institute
Atmospheric Environment | Year: 2015

Urban vegetation affects air quality through influencing pollutant deposition and dispersion. Both processes are described by many existing models and experiments, on-site and in wind tunnels, focussing e.g. on urban street canyons and crossings or vegetation barriers adjacent to traffic sources. There is an urgent need for well-structured experimental data, including detailed empirical descriptions of parameters that are not the explicit focus of the study.This review revealed that design and choice of urban vegetation is crucial when using vegetation as an ecosystem service for air quality improvements. The reduced mixing in trafficked street canyons on adding large trees increases local air pollution levels, while low vegetation close to sources can improve air quality by increasing deposition. Filtration vegetation barriers have to be dense enough to offer large deposition surface area and porous enough to allow penetration, instead of deflection of the air stream above the barrier. The choice between tall or short and dense or sparse vegetation determines the effect on air pollution from different sources and different particle sizes. © 2015 The Author.

Bagdadi O.,Swedish Road and Transport Research Institute
Transportation Research Part F: Traffic Psychology and Behaviour | Year: 2013

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. © 2012 Elsevier Ltd. All rights reserved.

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