Empirical Bayes method in the study of traffic safety via heterogeneous negative multinomial model

In the study of traffic safety, expected crash frequencies across sites are generally estimated via the negative binomial model, assuming time invariant safety. Since the time invariant safety assumption may be invalid, Hauer (1997) proposed a modified empirical Bayes (EB) method. Despite the modification, no attempts have been made to examine the generalisable form of the marginal distribution resulting from the modified EB framework. Because the hyper-parameters needed to apply the modified EB method are not readily available, an assessment is lacking on how accurately the modified EB method estimates safety in the presence of the time variant safety and regression-to-the-mean (RTM) effects. This study derives the closed form marginal distribution, and reveals that the marginal distribution in the modified EB method is equivalent to the negative multinomial (NM) distribution, which is essentially the same as the likelihood function used in the random effects Poisson model. As a result, this study shows that the gamma posterior distribution from the multivariate Poisson-gamma mixture can be estimated using the NM model or the random effects Poisson model. This study also shows that the estimation errors from the modified EB method are systematically smaller than those from the comparison group method by simultaneously accounting for the RTM and time variant safety effects. Hence, the modified EB method via the NM model is a generalisable method for estimating safety in the presence of the time variant safety and the RTM effects.

An examination of the microscopic simulation models to identify traffic safety indicators

Evaluating the safety of different traffic facilities is a complex and crucial task. Microscopic simulation models have been widely used for traffic management but have been largely neglected in traffic safety studies. Micro simulation to study safety is more ethical and accessible than the traditional safety studies, which only assess historical crash data. However, current microscopic models are unable to mimic unsafe driver behavior, as they are based on presumptions of safe driver behavior. This highlights the need for a critical examination of the current microscopic models to determine which components and parameters have an effect on safety indicator reproduction. The question then arises whether these safety indicators are valid indicators of traffic safety. The safety indicators were therefore selected and tested for straight motorway segments in Brisbane, Australia. This test examined the capability of a micro-simulation model and presents a better understanding of micro-simulation models and how such models, in particular car following models can be enriched to present more accurate safety indicators.

Traffic safety culture : what can we learn from Australia?

-- The role of traffic safety culture in Australia -- A comparison of drink driving (a success story) and speeding (a work in progress) ―Countermeasure approaches ―Community attitudes, perceptions and behaviors -- Lessons from Australia for the further development of the traffic safety culture concept

A framework for conceptualising traffic safety culture

Traffic safety culture is a relatively new concept which has recently gained attention in the field of traffic safety. There is currently little known regarding the nature of the concept, nor how it should be defined. Preliminary definitions have tended to focus on specific road safety problems and the anticipated effect of a strong traffic safety culture. The literature to date has tended to emphasise how traffic safety culture might be created or shaped. However, without a better understanding of the nature and structure of traffic safety culture, discussions regarding changes to traffic safety culture are restricted. An examination of different conceptualisations and definitions of organisational safety culture provides a preliminary theoretical framework for traffic safety culture. Two high risk driving behaviours within the Australian context are compared to illustrate how key factors within this framework can be used to understand and improve road safety outcomes.

The influence of fleet safety climate on occupational driver behaviours

The concepts of traffic safety culture and climate hold considerable impact on road safety outcomes. Data sourced from four Australian organisations revealed a five factor structure that was consistent with previous research, which were: management commitment; work demands; relationships; appropriateness of rules; and communication. Correlation and regression analyses were conducted to identify which aspects of fleet safety climate were related to driver behaviours. The findings suggest that organisations may be able to reduce the likelihood of employees engaging in unsafe driving behaviours as a result of fatigue or distractions through increasing aspects of fleet safety climate, including: management commitment; level of trust; safety communication; appropriateness of work demands; and appropriateness of safety policies and procedures. To assist practitioners in enhancing fleet safety climate and managing occupational road risks, recommendations are made based on these findings, such as fostering a supportive environment of mutual responsibility.

The effect of traffic lane widths on the safety of cyclists in urban areas

This literature review examines the relationship between traffic lane widths on the safety of road users. It focuses on the impacts of lane widths on motor vehicle behaviour and cyclists’ safety. The review commenced with a search of available databases. Peer reviewed articles and road authority reports were reviewed, as well as current engineering guidelines. Research shows that traffic lane width influences drivers’ perceived difficulty of the task, risk perception and possibly speed choices. Total roadway width, and the presence of onroad cycling facilities, influence cyclists’ positioning on the road. Lateral displacement between bicycles and vehicles is smallest when a marked bicycle facility is present. Reduced motor vehicle speeds can significantly improve the safety of vulnerable road users, particularly pedestrians and cyclists. It has been shown that if road lane widths on urban roads were reduced, through various mechanisms, it could result in a safety environment for all road users.

Evaluation of the GHR car following model for traffic safety studies

Traffic safety studies mandate more than what existing micro-simulation models can offer as they postulate that every driver exhibits a safe behaviour. All the microscopic traffic simulation models are consisting of a car-following model and the Gazis–Herman–Rothery (GHR) car-following model is a widely used model. This paper highlights the limitations of the GHR car-following model capability to model longitudinal driving behaviour for safety study purposes. This study reviews and compares different version of the GHR model. To empower the GHR model on precise metrics reproduction a new set of car-following model parameters is offered to simulate unsafe vehicle conflicts. NGSIM vehicle trajectory data is used to evaluate the new model and short following headways and Time to Collision are employed to assess critical safety events within traffic flow. Risky events are extracted from available NGSIM data to evaluate the modified model against the generic versions of the GHR model. The results from simulation tests illustrate that the proposed model does predict the safety metrics better than the generic GHR model. Additionally it can potentially facilitate assessing and predicting traffic facilities’ safety using microscopic simulation. The new model can predict Near-miss rear-end crashes.

Traffic safety at road-rail level crossings using a driving simulator and traffic simulation

A number of Intelligent Transportation Systems (ITS) were used with an advanced driving simulator to assess its influence on driving behavior. Three types of ITS interventions namely, Video in-vehicle (ITS1), Audio in-vehicle (ITS2), and On-road flashing marker (ITS3) were tested. Then, the results from the driving simulator were used as inputs for a developed model using a traffic micro-simulation (Vissim 5.4) in order to assess the safety interventions. Using a driving simulator, 58 participants were required to drive through a number of active and passive crossings with and without an ITS device and in the presence or absence of an approaching train. The effect of driver behavior changing in terms of speed and compliance rate was greater at passive crossings than at active crossings. The difference in speed of drivers approaching ITS devices was very small which indicates that ITS helps drivers encounter the crossings in a safer way. Since the current traffic simulation was not able to replicate a dynamic speed change or a probability of stopping that varies based on different ITS safety devices, some modifications of the current traffic simulation were conducted. The results showed that exposure to ITS devices at active crossings did not influence the drivers’ behavior significantly according to the traffic performance indicators used, such as delay time, number of stops, speed, and stopped delay. On the other hand, the results of traffic simulation for passive crossings, where low traffic volumes and low train headway normally occur, showed that ITS devices improved overall traffic performance.

Disability due to road traffic crashes and the management of road safety in developing countries

Injury as a result of road traffic crashes is one of the most significant public health problems in developing countries. It intersects with disability as a development issue because a substantial proportion of people injured in road traffic crashes experience disability, both short term and long term. While there have been significant steps towards better management of road safety globally, especially in developing countries, the implications for road safety policy and practice of disability due road traffic crashes is not fully appreciated. In particular, qualitative information on the lived experience people with a long term disability as a result of a road traffic crash can inform better road safety policy and practice, as demonstrated in a case study from Thailand. The benefits of better policies and practices are likely to accrue to a wide range of road users, and to contribute to the achievement of sustainable development.

Policing of road safety in Oman: Perceptions and beliefs of traffic police officers

With increasing motorisation, road safety has become a major concern within Oman. Internationally, traffic policing plays a major role in improving road safety. Within Oman, the Royal Oman Police's (ROP) Directorate General of Traffic is responsible for policing traffic laws. Many common enforcement approaches originate from culturally different jurisdictions. The ROP is a relatively young policing force and may have different operational practices. Prior to applying practices from other jurisdictions it is important to understand the beliefs and expectations within the Directorate General of Traffic. Further, there is a need for individuals to understand their role and what is expected of them. Therefore, it is important to explore the agreement between levels of the ROP to determine how strategies and expectations transfer within the organisation. Interviews were conducted with 19 police officers from various levels of the ROP. A number of themes and findings emerged. Individuals at the upper level of the traffic police had a clear knowledge of the role of the ROP, believed that traffic police know what is expected of them, are well trained in their role and can have a very positive influence on road safety. These beliefs were less certain lower within the organisations with traffic officers having little knowledge of the role of the ROP or what was expected of them, felt undertrained, and believed their peers have little positive impact on road safety. There is a need to address barriers within the ROP in order to positively impact road safety.

Schools' guide : How to select providers of road safety education programs for senior school students

Road safety education is not just about safe driving. Best practice road safety education seeks to improve knowledge and change attitudes relating to being safe, and making sure others are safe on the road. Typical topics might include: • Strengthening attitudes toward safe road use behaviours and avoiding risks • Supporting behaviours to ensure others are safe • Promoting knowledge of traffic rules.

The role of traffic violations in police-reported bicycle crashes in Queensland

Media articles have promoted the view that cyclists are risktakers who disregard traffic regulations, but little is known about the contribution of cyclist risk-taking behaviours to crashes. This study examines the role of traffic violations in the 6774 police-reported bicycle crashes in Queensland between January 2000 and December 2008. Of the 6328 crashes involving bicycles and motor vehicles, cyclists were deemed to be at fault in 44.4% of the incidents. When motorists were determined to be at-fault, ‘failure to yield’ violations accounted for three of the four most reported contributing factors. In crashes where the cyclist was at fault, attention and inexperience were the most frequent contributing factors. There were 67 collisions between bicycles and pedestrians, with the cyclist at fault in 65.7%. During the data period, 302 single-bicycle crashes were reported. The most frequent contributing factors were avoidance actions to miss another road user and inattention or negligence.

Impact of traffic oscillations on freeway crash occurrences

Traffic oscillations are typical features of congested traffic flow that are characterized by recurring decelerations followed by accelerations (stop-and-go driving). The negative environmental impacts of these oscillations are widely accepted, but their impact on traffic safety has been debated. This paper describes the impact of freeway traffic oscillations on traffic safety. This study employs a matched case-control design using high-resolution traffic and crash data from a freeway segment. Traffic conditions prior to each crash were taken as cases, while traffic conditions during the same periods on days without crashes were taken as controls. These were also matched by presence of congestion, geometry and weather. A total of 82 cases and about 80,000 candidate controls were extracted from more than three years of data from 2004 to 2007. Conditional logistic regression models were developed based on the case-control samples. To verify consistency in the results, 20 different sets of controls were randomly extracted from the candidate pool for varying control-case ratios. The results reveal that the standard deviation of speed (thus, oscillations) is a significant variable, with an average odds ratio of about 1.08. This implies that the likelihood of a (rear-end) crash increases by about 8% with an additional unit increase in the standard deviation of speed. The average traffic states prior to crashes were less significant than the speed variations in congestion.

Car following model improvement for traffic safety metrics reproduction

Car Following models have a critical role in all microscopic traffic simulation models. Current microscopic simulation models are unable to mimic the unsafe behaviour of drivers as most are based on presumptions about the safe behaviour of drivers. Gipps model is a widely used car following model embedded in different micro-simulation models. This paper examines the Gipps car following model to investigate ways of improving the model for safety studies application. The paper puts forward some suggestions to modify the Gipps model to improve its capabilities to simulate unsafe vehicle movements (vehicles with safety indicators below critical thresholds). The result of the paper is one step forward to facilitate assessing and predicting safety at motorways using microscopic simulation. NGSIM as a rich source of vehicle trajectory data for a motorway is used to extract its relatively risky events. Short following headways and Time To Collision are used to assess critical safety event within traffic flow. The result shows that the modified proposed car following to a certain extent predicts the unsafe trajectories with smaller error values than the generic Gipps model.