Road traffic accidents are a serious burden to the health systems of many countries especially in South Africa. Research aimed at reducing traffic related accidents is of importance as traffic crashes are rated as the second leading cause of fatalities in South Africa and ninth in the world. Despite the extensive efforts into research and development of new technology, driver fatigue still remains a cause of vehicle accidents worldwide. Fatigue plays a role in up to 20% of vehicle accidents with many being serious or fatal. Numerous coping behaviours are employed by drivers to counteract the negative effects of fatigue. The most common coping behaviours include taking short naps, talking to passengers, listening to the radio, opening windows and drinking stimulants. Driving breaks have long been identified as an effective countermeasure against fatigue. Most research done in driving breaks has investigated the duration of the breaks, activity undertaken during the break and the frequency of the breaks taken outside the vehicle. However limited literature is available on the effectiveness of breaks in counteracting the effects of fatigue. The objective of the current study was aimed at assessing whether short duration breaks are an effective countermeasure against fatigue. Physiological, neurophysiological, subjective and performance measures were used as indicators for fatigue. Additional focus of the research was determining whether breaks were more or less effective at counteracting the effects of fatigue at different times of day. Twelve participants were recruited for the study, six males and six females. The participants were required to perform a driving task on a simulator for 90 minutes. The study consisted of four independent conditions, namely driving during the day with breaks, driving during the day without breaks, driving during the night with breaks and driving during the night without breaks. The without breaks conditions were similar except that they occurred at different times of the day, one session at night and the other session during day time, as was the case for the conditions with breaks. The driving task used in the current study was a low fidelity simulator tracking task. The participants were required to follow a centre line displayed on a tracking path as accurately as possible. The measurements that were recorded in this study included physiological, performance, subjective and neurophysiological. Physiological measures included heart rate and heart rate variability (frequency domain) and core body temperature. The ascending threshold of the critical flicker fusion frequency was the only neurophysiological measurement included in the current investigation. Performance was quantified by mean deviation from a centre line participants were meant to track. Two rating scales were used: Karolinska sleepiness scale and the Wits sleepiness scale were used for the measurement of subjective sleepiness. Heart rate, heart rate variability and mean deviation were measured continuously throughout the 90 minute driving task. Critical flicker fusion frequency, temperature and the subjective scales were measured before and after the 90 minute driving task. The results indicated that the short duration breaks during day time had a positive effect on driving performance; however the breaks at night had a negative effect on driving performance. Heart rate was higher during the day compared to night time and the heart rate variability high frequency spectrum values were lower during the day condition, to show the activation of the sympathetic nervous system which is characteristic of day time. The night conditions had lower heart rate values and higher heart rate variability high frequency values, which show the activation of the parasympathetic nervous system which is dominant during periods of fatigue and night time. Subjective sleepiness levels were also higher at night compared to day time.

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The next generation of intelligent vehicles will evolve from being able to drive autonomously to ones that communicate with other vehicles and execute joint behaviors. Before allowing these vehicles on public roads, we must guarantee that they will not cause accidents. We will apply formal methods to ensure the degree of safety that cannot be assured with simulation or closed-track testing. However, there are challenges that need to be addressed when applying formal verification techniques to cooperative driving systems. This thesis focuses on the techniques that address the following challenges: 1. Automotive applications interact with the physical world in different ways; 2. Cooperative driving systems are time-critical; 3. The problem of state explosion when we apply formal verification to systems with more participants. First, we describe the multiple stack architecture. It combines several stacks, each of which addresses a particular way of interaction with the physical world. The layered structure in each stack makes it possible for engineers to implement cooperative driving applications without being bogged down by the details of low-level devices. Having functions arranged in a layered fashion helps us divide the verification of the whole system into smaller subproblems of independent module verification. Secondly, we present a framework for modeling the protocol systems that uses GPS clocks for synchronization. We introduce the timing stack, which separates a process into two parts: the part modeled as an finite-state machine that controls state transitions and messages exchanges, and the part that determines the exact moment that a timed event should occur. The availability of accurate clocks at different locations allows processes to execute actions simultaneously, reducing interleaving that often arises in systems that use multiple timers to control timed events. With accurate clocks, we create a lock protocol that resolves conflicting merge requests for driver-assisted merging. Thirdly, we introduce stratified probabilistic verification that mitigates state explosion. It greatly improves the probability bound obtained in the original probabilistic verification algorithm. Unlike most techniques that aim at reducing state space, it is a directed state traversal, prioritizing the states that are more likely to be encountered during system execution. When state traversal stops upon depleting the memory, the unexplored states are the ones that are less likely to be reached. We construct a linear program whose solution is the upper bound for the probability of reaching those unexplored states. The stratified algorithm is particularly useful when considering a protocol system that depends on several imperfect components that may fail with small but hard-to-quantify probabilities. In that case, we adopt a compositional approach to verify a collection of components, assuming that the components have inexact probability guarantees. Finally, we present our design of driver-assisted merging. Its design is reasonably simplified by using the multiple stack architecture and GPS clocks. We use a stratified algorithm to show that merging system fails less than once every 5 × 10¹³ merge attempts.

Adverse weather is considered as one of the important factors contributing to injuries and severe crashes. During rainy conditions, it can reduce travel visibility, increase stopping distance, and create the opportunity hydroplaning. This study quantified the relative crash risk on Oregon 217 southbound direction under rainy conditions by using a match-paired approach, applied one-year traffic data, crash data and NEXRAD Level II radar weather data. There are 26 crashes occurred in match-paired weather conditions for Oregon 217 in year 2007. The results of this study indicate that a higher crash risk and a higher property-damage-only crash risk occurred during rainy days. The crash risk level varies by the location of the highway, at milepost 2.55 station SW Allen Blvd has the highest driving risks under rainy conditions.

Thesis (MScEng (Mechanical and Mechatronic Engineering))--University of Stellenbosch, 2007. / Vehicles are expected to deliver adequate power for the engine size and vehicle class. They must also deliver good response to the driver’s desired action as well as deliver the lowest possible fuel consumption in all possible conditions and comply with emissions regulations. The combination of these factors is termed good driveability. Evaluating driveability is time and cost intensive and is most commonly evaluated from a subjective driver prospective. Advanced control systems allow for more accurate control of the vehicles response to the drivers demands. The objective of this document was to develop a quantitative driveability evaluation model for engine management calibration. The important aspects of engine management control for driveability, as well as how they are manipulated to deliver acceptable driveability were identified. Test procedures were developed to measure and quantify all these important factors. The test procedures can be evaluated for their different sections or for a complete driveability evaluation method. An optimised driveability evaluation method was developed to reduce the driveability evaluation time. Verification of the driveability evaluation model did provide different results for a different engine management calibration.

published_or_final_version / Sociology / Master / Master of Philosophy

Only circumscribed aspects of highway aggression have been investigated. The upsurge of abuse and violence transpiring between motorists necessitated a more definitive depiction of the actual events, participants, and relevant contextual features. A questionnaire administered to 120 motorists, aged 18 to 68, solicited a recountal of incidents occurring within 12 months and a description of their most recent encounter. Based on severity of experience, subjects were relegated to distal threat, direct threat, and nonvictim groups. Although most events involved unreported distal threats lasting less than three minutes, men and non-college graduates were more often directly threatened, while non-victims were predominantly women and college graduates. Perpetrators were primarily unknown Caucasian males who generally aggressed in populated areas during afternoon hours.

The proposed study examined the role of anxiety and risk-taking in driving performance in adolescents. In addition to examining the sample as a whole, gender differences were assessed given earlier reports from our laboratory and others indicating that males and females differ with respect to risky behaviors to driving performance and anxiety. Adolescents' subjective and physiological responses to a driving simulator task were assessed. Anxiety was measured via self report and salivary cortisol. Participants provided a baseline saliva sample and 3 post-task samples for cortisol analysis. Subjective anxiety scores were obtained at both baseline and following the driving stressor. Information concerning impulsivity, as well as other psychological constructs was also collected at baseline. Unlike the pilot study, there were no relationships (with or without respect to gender) between salivary cortisol and both self-reported anxiety (state and trait) or impulsively measures for this sample. These results suggest that this group of adolescents may not have been anxious about the driving task. This discrepancy may stem from error introduced by the smaller sample size obtained from the initial findings or to other factors remaining outside the parameters of the current study. The task did, however, induce a slight hypothalamic pituitary adrenal (HPA) axis response indicating some physiological arousal. Males had significantly higher cortisol levels at baseline than females and at time point 3 while approaching significance at time points 2 and 4. Females possessed significantly higher trait anxiety than males and all post task cortisol levels were positively correlated to age while time points 2 and 4 (with time point 3 approaching significance, p=0.09) were inversely correlated with Self Depreciation scores. Additionally, females had Persecutory Ideas scores that were also negatively correlated with cortisol at time points 3 and 4. For both the entire sample and males only, the correlation between post-task cortisol and driving performance was positive and approached significance (p=0.07 and p=0.08, respectively), suggesting that some HPA activation may be facilitative for successful driving task performance. Correlations between driving performance and psychological constructs were explored and discussed with and without respect to gender.

Stereotype threat refers to the pressure that individuals feel when they are at risk of confirming a demeaning stereotype about themselves. Research has found that stereotype threat impairs performance on cognitive-based tasks by inducing mental interference (e.g., Schmader & Johns, 2003). This thesis hypothesised that this finding would generalise to driving and that drivers who are better able to inhibit cognitive interference (i.e., with better inhibitory ability) would be less susceptible to the disruptive effect of stereotype threat than drivers who are less able (i.e., with poorer inhibitory ability). A series of three experiments conducted in a driving simulator tested the predictions using the gender stereotype of driving skills and investigated the interpretation of the results. The experiments revealed that stereotype threat exerted both a facilitative and debilitative influence on driving performance, as indicated by different performance measures. The facilitative effect diminished when drivers experienced increased mental demands or when they were assessed by an unexpected performance measure, while the debilitative effect was more likely observed among drivers who received negative feedback than drivers who received positive feedback. Moreover, the results supported the prediction that inhibitory ability would moderate the detrimental impact of stereotype threat as the performance of drivers with poorer inhibitory ability was impeded more than that of drivers with better inhibitory ability. Regarding the processes underlying the present findings, the experiments provided suggestive evidence that stereotype threat elicits cognitive interference and simultaneously motivates drivers to concentrate on particular performance areas in an attempt to refute the stereotype. In combination, these processes appear to be at least partly responsible for the performance deficits and boosts observed.

Low speed urban streets are designed to provide both access and mobility, and accommodate multiple road users, such as bicyclists and pedestrians. However, speeds on these facilities often exceed the intended operating speeds as well as their design speeds. Several studies have indicated that the design speed concept, as implemented in the roadway design process in the United States, does not guarantee a consistent alignment that promotes uniform operating speeds less than design speeds. To overcome these apparent shortfalls of the design speed approach, a promising design approach is a performance-based design procedure with the incorporation of operating speeds. Under this procedure, the geometric parameters of the roadways are selected based on their influences on the desired operating speeds. However, this approach requires a clear understanding of the relationships between operating speeds and various road environments. Although numerous studies have developed operating speed models, most of these previous studies have concentrated on high speed rural two-lane highways. In contrast, highway designers and planners have very little information regarding the influence of low speed urban street environments on drivers' speeds. This dissertation investigated the relationship between drivers' speed choices and their associated low speed urban roadway environments by analyzing second-by-second in-vehicle GPS data from over 200 randomly selected vehicles in the Atlanta, Georgia area. The author developed operating speed models for low speed urban street segments based on roadway alignment, cross-section characteristics, roadside features, and adjacent land uses. The author found the number of lanes per direction of travel had the most significant influence on drivers' speeds on urban streets. Other significant variables include on-street parking, sidewalk presence, roadside object density and offset, T-intersection and driveway density, raised curb, and adjacent land use. The results of this research effort can help highway designers and planners better understand expected operating speeds when they design and evaluate low speed urban roadways.