Temporal fluctuations in driving demand: The effect of traffic complexity on subjective measures of workload and driving performance

Traffic density has been shown to be a factor of traffic complexity which influences driver workload. However, little research has systematically varied and examined how traffic density affects workload in dynamic traffic conditions. In this driving simulator study, the effects of two dynamically changing traffic complexity factors (Traffic Flow and Lane Change Presence) on workload were examined. These fluctuations in driving demand were then captured using a continuous subjective rating method and driving performance measures. The results indicate a linear upward trend in driver workload with increasing traffic flow, up to moderate traffic flow levels. The analysis also showed that driver workload increased when a lane change occurred in the drivers’ forward field of view, with further increases in workload when that lane change occurred in close proximity. Both of these main effects were captured via subjective assessment and with driving performance parameters such as speed variation, mean time headway and variation in lateral position. Understanding how these traffic behaviours dynamically influence driver workload is beneficial in estimating and managing driver workload. The present study suggests possible ways of defining the level of workload associated with surrounding traffic complexity, which could help contribute to the design of an adaptive workload estimator.     

An analysis of public posting in reducing speeding behavior on an urban highway

The effects of public posting on speeding behavior on an urban highway were assessed using a reversal design. During baseline the percentage of drivers speeding was measured with a concealed radar unit. During the daily posting condition a highway sign was installed which provided feedback on the percentage of drivers not speeding yesterday and the best record to date. This sign was then covered and reintroduced. Results indicated that the sign was effective in reducing speeding behavior. Furthermore, the effects were most pronounced in reducing the speeds of the faster drivers. Next, daily and weekly postings were compared with the sign alone without numerical feedback: results revealed that the weekly posting condition was as effective as the daily posting condition, but that the sign had no influence when numbers were not posted. Finally, the weekly posting procedure remained effective during a 6-month follow-up condition.     

Adaptation of the safe driving climate among friends scale in Chinese drivers and its associations with risky driving behaviours

The present study aimed to adapt the Safe Driving Climate among Friends Scale (SDCaF) to Chinese drivers and to examine its reliability and validity. Three hundred and sixty drivers aged from 18 to 24 years old were asked to complete the SDCaF and the Risky Driving Behaviour Scale. A confirmatory factor analysis (n = 360) was conducted to examine the factorial structure of the SDCaF. The validity of the scale was then evaluated by examining the associations between the SDCaF factors, risky driving behaviours and traffic violations. The CFA results showed that the model fit of the Chinese version of the scale (SDCaF-C) was acceptable. Second, the SDCaF-C factors were weakly or moderately correlated with speeding, self-assertiveness and rule violations. Third, significant gender differences were found for the variables of friend pressure and communication, with male drivers scoring higher than female drivers. Moreover, drivers who had traffic violations in the past year scored higher on friend pressure and lower on both communication and shared commitment to safe driving compared to those who had not had traffic violations. The findings supported the psychological properties of the SDCaF-C and highlighted the importance of concerning the effects of safe diving climate among friends on young drivers’ risky driving behaviours.     

Limiting speed,towards an intelligent speed adapter (ISA)

This study concerns the effects of a prototype intelligent speed adapter (ISA) on speeding in actual traffic. Twenty-four subjects were included in a test of effects of feedback on speed behaviour, mental workload and acceptance. Subjects drove an instrumented vehicle in normal traffic on various types of roads with different speed restrictions. Subjects completed the test route twice, half of the subjects received specific feedback in the second trial (experimental group), half of the subjects did not (control group). The groups differed in several ways, the most important being adaptation of their behaviour after feedback. Subjects in the experimental group behaved more according to traffic rules, in particular speed limits, than subjects in the control group. No significant differences in workload were found. Two types of feedback were tested to acceptance and were rated differently.     

Effects of weather and weather forecasts on driver behaviour

Winter-time slipperiness is a considerable source of elevated road accident risk, especially in northern countries such as Canada, Finland and Sweden. The national road administrations often offer a service to inform drivers of forthcoming weather and driving conditions in different regions. This study addressed the effects of adverse weather and traffic weather forecasts on driver behaviour in Finland. Drivers (n = 1437) answered a questionnaire on perceptions of weather, self-reported driving behaviour, pre-trip acquisition of weather information, and possible travel plan changes. The questionnaires were distributed and instantaneously collected in rural service stations in different weather and driving conditions. Data from traffic weather forecasts, automatic traffic counters and weather measurement stations concerning the same area (and road) were also collected. Acquisition of weather information for the trip was associated with low recent driving experience, increasing age, female gender, long trip in question and very poor (local) conditions perceived by the driver. Drivers who had acquired information had also made more changes to travel plans, but information acquisition did not have an effect on their on-road driving behaviour. However, they estimated prevailing risks higher than those who did not acquire weather information. Drivers generally considered the driving conditions better than the forecast, but significantly less so in darkness than in daylight or civil twilight. Leisure trips were clearly underrepresented during very poor driving conditions forecasts, suggesting that some trips are postponed as a result of adverse weather conditions or forecasts thereof. Drivers reported various kinds of compensatory behaviour during adverse conditions, including a 6–7 km/h target speed decrement. This corresponded to traffic flow speed measurements. The results suggest that the on-road driving behaviour is predominantly affected by the prevailing observable conditions, rather than traffic weather forecasts. It is suggested that if administrators wish to help drivers in adjusting their on-road behaviour in adverse weather conditions, the methods should be more local and technical by nature.     

Exploring the effects of the location of the lane-end sign and traffic volume on multistage lane-changing behaviors in work zone areas: A driving simulator-based study

The lane-changing behavior in work zone areas has special features than a regular lane change as the former is usually compulsively motivated involving complicated cognitive processes with drivers’ perception of work-zone control devices. Toward this end, this study conducted a driving simulator-based experiment to understand the effects of lane-end sign distance and traffic volume on driving behaviors. A conceptual model was also proposed to partition the whole lane-changing process into three stages, i.e. the perception, preparation and action stages, reflecting different cognitive and manipulative activities of drivers. In addition to the lane-end sign distance and traffic volume, gender and profession of drivers were adopted as covariates. In this experiment, a complete combination of lane-end sign distance and traffic volume served as treatments. The results verify the impacts of those factors on driving behaviors in and across different stages. For example, the location of the lane-end sign had a profound influence on drivers' perception of the imminent work-zone situation, but the influence continued to diminish in the following two stages. On the other hand, male or taxi drivers tended to act earlier than female or regular drivers respectively, for all the three stages. According to the analysis, several practical implications were also provided. In specific, the lane-end sign is recommended to be installed 500 m upstream to the lane dropping point of work zones. It is a pioneer study toward investigating multistage driving behaviors in work zone areas, which is expected to provide references and guidance for the design of traffic control devices and other driving simulator-based studies.     

An eye-tracking study of the effects of dimensions of speed limit traffic signs on a mountain highway on driverś perception

Signs control and regulate traffic, anticipating potential dangers, prescribing correct behaviors, and disambiguating likely conflicts in priority. In Brazil, traffic accidents on highways located in mountain rural areas are mainly related to the design of roads and speeding, rather than to the impact of traffic flow. Since drivers highly depend on their visual perceptions for adopting driving behaviors, this study analyzes driver perception during a trip and the response of this parameter to changes in the diameter of vertical speed limit signs in a driver simulator equipped with an eye-tracking system. The objective was to investigate whether an increase in the plate size would enhance driver perception and influence drivers’ compliance with speed limits. Fifty-five volunteers were asked to drive twice on a 10-km mountain route, after which one of the diameters, namely 75, 100, 120, and 150 cm, used according to several Brazilian and American standards, was randomly chosen. The results showed the size of the traffic signs did not affect dependent variables number of fixations, percentage of perceived signals, time of observation, perception distance, and non-compliance with the speed limit. The most significant result was the relationship between speed variability and guided round, since the driver’s performance was improved with the distance along the studied stretch. The outcomes can be useful for the development of strategies that manage speeding on roads by improving and implementing low-cost interventions in low-income countries.     

Are you a “bad driver” all the time? Insights from a weekly diary study on personality and dangerous driving behavior

Research concerning dangerous driving behavior has often favored studying inter-individual differences at the expense of intra-individual ones (especially when verifying its associations with personality factors). Using a 7 weeks diary approach, we aimed at exploring the intra-individual variation of dangerous driving behavior (Errors, Violations and Aggressive driving). Also, we verified if our outcomes could be predicted by both situational variables (weekly km, felt traffic pressure and traffic mood) and dispositional ones (Big-Five personality factors, age and gender). Our findings revealed that Violations, Verbal & Physical aggression and Vehicle aggression had similar intra- to inter-individual variation ratios, with approximately 45% of variance at the intra-individual level. In contrast, Errors had only about 30% of variance at the intra-individual level. Traffic mood was the only significant intra-individual predictor, negatively correlating with all outcomes. Excepting Agreeableness, all personality factors were related to at least one dangerous driving behavior (especially consistent for the association between Extraversion and Aggressive driving). Also, women reported lower levels than men on all outcomes but Errors. Overall, this study raises some questions about the assumed stability of driving behavior, while at the same time confirming several relational patterns between personality factors and dangerous driving.     

Feedback interventions and driving speed: A parametric and comparative analysis

Five experiments were conducted to assess the effects of several variables on the efficacy of feedback in reducing driving speed. Experiment 1 systematically varied the criterion used to define speeding, and results showed that the use of a lenient criterion (20 km/hr over the speed limit), which allowed for the posting of high percentages of drivers not speeding, was more effective in reducing speeding than the use of a stringent criterion (10 km/hr over the speed limit). In Experiment 2 an analysis revealed that posting feedback reduced speeding on a limited access highway and the effects persisted to some degree up to 6 km. Experiments 3 and 4 compared the effectiveness of an unmanned parked police vehicle (Experiment 3) and a police air patrol speeding program (Experiment 4) with the feedback sign and determined whether the presence of either of these enforcement variables could potentiate the efficacy of the sign. The results of both experiments demonstrated that although the two enforcement programs initially produced larger effects than the feedback sign, the magnitude of their effect attenuated over time. Experiment 5 compared the effectiveness of a traditional enforcement program with a warning program which included handing out a flier providing feedback on the number and types of accidents occuring on the road during the past year. This experiment demonstrated that the warning program produced a marked reduction in speeding and the traditional enforcement program did not. Furthermore, the warning program and a feedback sign together produced an even greater reduction in speeding than either alone.     

Effects of public posting on driving speed in Icelandic traffic

We replicated a study by Van Houten, Nau, and Marini (1980) that had revealed reductions in vehicle speeding following the posting of percentages of drivers not speeding on a sign at roadside. Our subjects were drivers entering a residential area where the speed limit changed from 90 km/hr (55.9 mph) to 60 km/hr (37.3 mph). A total of 4,409 vehicle speeds were taken from two observation sessions per day for 20 consecutive weekdays. The intervention consisted of a single posting condition, in which a hypothetical daily percentage of drivers not speeding was posted on a feedback sign, followed by a double posting condition, in which a sign posting a best result was erected beyond the feedback sign. Results revealed a significant speed reduction from an average of 69.0 km/hr (42.9 mph) during baseline to 63.4 km/hr (39.4 mph) during single posting. Average speed during double posting was 62.9 km/hr (39.1 mph). The percentage of drivers exceeding 70 km/hr (43.5 mph) dropped from 41.0 during baseline to 20.5 during single posting. The significant speed reductions add to the generality of findings of similar studies in Canada and Israel and offer possible explanations for the failure of feedback posting to reduce speed in the U.S.     

The effect of context and drivers’ age on highway traffic signs comprehension

Background: Comprehension of traffic signs is crucial to safety. Objectives: To test the effects of the presentation condition (with or without driving context) on symbolic based road signs comprehension and comprehension time for young and older drivers. Method: 50 young drivers and 50 older drivers were presented with images of 28 Israeli road signs, both without context (with a white background) and in context (with the driving surrounding). Data were collected on the accuracy of signs meaning and on the time it took the participants to provide the meaning. Results: Younger drivers performed significantly better than older drivers on both accuracy and response time (RT). Older drivers’ average RT was approximately twice as long as younger drivers’ RT. However, the presentation mode (with or without context) did not affect sign comprehension of either group, but the presence of the context did increase the time it took the drivers to comprehend the sign’s meaning. In addition, correct response time was similar to opposite to sign’s meaning response time. Implications: Older drivers, can benefit from retraining in sign comprehension of current signage. The training should involve signs in their natural road environment to reduce comprehension time while actually driving. Moreover, signs that were understood as having an opposite meaning should be redesigned or be accompanied by text.     

Using a multi-user driving simulator system to explore the patterns of vehicle fleet rear-end collisions occurrence under different foggy conditions and speed limits

Vehicle fleet rear-end collisions (FRECs) are an extremely fatal type of traffic collisions on freeway and they usually occur in foggy weather. This study aimed to explore the patterns of vehicle fleet rear-end collisions occurrence under different foggy conditions and speed limits on freeway. A multi-user driving simulator system was used to conduct the experiment and the driving behavior data were collected from eight participants. The experimental results showed that as the fog density increased, the length of vehicle fleet decreased significantly, and drivers tended to keep a more stable car-following distance. The fog weather and short vehicle gap prompted drivers to react faster and brake harder in respond to the leading vehicle’s brake. In spite of the compensational behaviors, more FRECs were observed under heavy fog condition. Lowering speed limit can significantly reduce the FRECs under foggy conditions. As the speed limits reduced, drivers’ brake response time and speed variance significantly reduced. The study also found that drivers’ brake response time was negatively correlated with their positions in the fleet. Drivers in the front positions of the fleet had a longer response time than drivers in the back positions and thus were more likely to encounter collisions. The study generated a better understanding of drivers’ behavioral pattern in a vehicle fleet and the patterns of vehicle fleet rear-end collisions occurrence. The findings also shed lights on the design of driver assistance system for complex driving situations such as freeway driving under adverse weather.     

Analysis of driver’s decision distance and merging distance in work zone area based on parametric survival models: With the aid of a driving simulator experiment

Work zones affect traffic safety and efficiency by changing the road condition and drivers’ maneuver. Therefore, it is important to fully understand drivers’ merging behavior in work zone related areas. In this study, a model framework composed of decision-distance analysis and merging-distance analysis was proposed, which could describe both decision-making and lane-changing process of merging behavior. A road environment with work zone was developed based on a driving simulator, and six scenarios composed of two levels of traffic volume and three different lane-end sign’s locations were designed. Forty-two licensed participants, including 21 females (10 professional drivers vs. 11 normal drivers) and 21 males (15 professional drivers vs. 6 normal drivers) finally completed the experiment. Based on the experimental data, parametric survival models were established to analyze the effects of traffic sign location, traffic situation and driver characteristics on drivers’ decision distance and merging distance. The results showed that: (i) the lane-end sign’s location affected the decision point of lane changing and further affected the merging distance. However, the effect was weakened when the sign was placed far away from the work zone; (ii) merging distance in high traffic volume condition was shorter than that in low traffic volume condition; (iii) work zone posed greater challenges for female drivers as they merged later than males, and females were reluctant to adjust their merging distance according to different gap conditions. The findings shed some light on the future improvement of traffic design and management in work zones.     

Relations between a laboratory-based sustained attention task and traffic violations in an Iranian sample of drivers

The role of cognitive abilities regarding driver behavior is crucially important in the occurrence of traffic violations and preventing tragic motor vehicle collisions. Sustained attention is one cognitive ability that may contribute to safe driving behavior. The present study investigated the relation between sustained attention and traffic violations. One hundred and one Iranian male drivers (age: M = 37.17, SD = 8.37) with at least 2 years driving experience voluntarily participated in the study. Participants were categorized into two groups based on the number of driving rule violations they committed over the last 2 years (n = 48 clean record, n = 53 violators). Sustained attention was measured by performance on the Conjunctive Continuous Performance Task (CCPT). Four CCPT performance measures were computed: (1) Mean reaction time for correct responses (M-RT); (2) standard deviation of reaction times for correct responses (SD-RT); (3) percent of omission errors (failure to respond to target stimulus); (4) percent of commission errors (identification of a non-target stimulus as target). Results showed after controlling for age and education, there was a significant group difference on M-RT, indicating that individuals with no traffic violations had faster reaction times as compared to those who had 1 or more traffic violations. No effect of group on any of the other outcomes was present after correcting for alpha inflation. When assessing the effect of age and education, education was significantly related to average reaction time and percent of omission errors. No significant effect of age was apparent. Findings suggest cognitive function, specifically sustained attention measured with a laboratory-based measure, may be associated with safe driving behavior.     

The effects of motion on in-vehicle touch screen system operation: A battle management system case study

The use of in-vehicle touch screen devices is currently common in both military and civilian vehicles; despite this, the effects of motion on touch screen device operation within vehicles remains largely unexplored. This article describes a study that examined, using driving simulation, the influences of motion on performance, workload and usability when using a touch screen in-vehicle battle management system. Acting in the role of battle management system operator, 20 participants undertook four simulated drives, two under high motion (representative of an unsealed road) and two under normal motion (representative of a sealed road), whilst performing various battle management tasks. In the high motion condition, lower accuracy and longer task completion times were found, along with greater levels of subjective and physiological workload and lower levels of perceived device usability, when compared to the normal motion condition. The findings indicate that, compared to normal motion, the high motion condition impaired key aspects of battle management system operation. In closing, the importance of considering motion and its effects during touch screen system design is discussed.     

Evaluation of an integrated lighting-warning system on motorists’ yielding at unsignalized crosswalks during nighttime

Drivers’ yielding behavior to pedestrians during nighttime was assessed in seven different conditions of crosswalk lighting: (a) baseline condition with standard road lighting; (b) enhanced LED lighting that increased lighting level from 70 to 120 lx; (c) flashing orange beacons on top of the backlit pedestrian crossing sign; (d) in-curb LED strips on the curbsides of the zebra crossing with steady light emission; (e) in-curb LED strips with flashing light emission; (d) all previous devices activated with in-curb LED strips in steady mode; (e) all previous devices activated with in-curb LED strips in flashing mode. For every condition 100 trials were recorded with a staged pedestrian that initiated a standardized crossing when a vehicle was approaching. The frequency of drivers’ yielding was computed for each condition. A significant increase for yielding compliance was recorded from standard road lighting to enhanced dedicated lighting (19–38.21%), and from enhanced dedicated lighting to the seventh condition with the flashing beacons and the flashing in-curb LED strips activated (38.21–63.56%). The results showed that the integrated lighting-warning system for pedestrian crossings was effective in increasing motorists’ yielding to pedestrians during nighttime.     

The factors of female taxi drivers’ speeding offenses in Taiwan

Females choosing taxi driving as a career is rare, therefore, investigating such samples is often difficult. Speeding is one of the most common driving violations, however, there has been no research looking into female taxi drivers’ speeding issue. This study explores the factors of female taxi drivers’ speeding offenses in Taiwan. Data is based on a national survey and includes 235 professional female taxi drivers. The results indicate that female taxi drivers work approximately 27.37 days per month, at a mean of 9.76 h per day. Of the female taxi drivers represented in this study, 22.8% reported at least one speeding offense over a one-year period. The results of a logistic regression model reveal that the determinant factors associated with female taxi drivers’ speeding offenses are significantly related to age, educational level and mileage driven. However, job experience, business operating style, and vehicle engine size are not associated with committing speeding offenses. Practical implications for traffic safety of female taxi drivers are also discussed.     

Professional and non-professional drivers’ stress reactions and risky driving

The aim of the present study was to investigate stress reactions, speeding, number of penalties and accident involvement among different driver groups (taxi drivers, minibus drivers, heavy vehicle drivers, and non-professional drivers). A total number of 234 male drivers participated in the study. The participants were asked to complete the Driver Stress Inventory (DSI) together with a demographic information form. Five dimensions of the DSI were measured; aggression, dislike of driving, hazard monitoring, fatigue proneness, and thrill-seeking. After controlling the effects of age and annual mileage, the results of the ANCOVAs revealed differences between different driver groups in terms of both risky driving behaviours and stress reactions in traffic. Regression analyses indicated that aggression, dislike of driving, and hazard monitoring dimensions of the DSI were related to accident involvement after controlling for the effects of age, annual mileage and driver group. Dislike of driving and thrill-seeking dimensions of the DSI were related to speeding on in-city roads.     

驾驶员选择性注意过程中的规则图式启动效应

本研究将驾驶无意视盲范式与交通违规事件识别任务相结合, 通过两个实验分别探究任务性质(有提示、无提示)和规则图式训练(训练、未训练)对驾驶员识别交通信号和违规事件的影响。结果发现, 交通规则提示能够提高有经验的驾驶员识别交通信号的正确率(实验1); 对于新手驾驶员, 则需要结合规则图式训练才能起到相同效果(实验2)。研究表明驾驶员选择性注意过程中存在规则图式启动效应, 图式训练能够弥补新手驾驶员经验的不足。     

Road-sign utility as judged by drivers with different amounts of driving experience

This study starts from the hypothesis that sign perception depends on the motivational valences of signs. Two groups of drivers with different amounts of driving experience rated Swedish road signs on dimensions assumed to indicate perceived sign utility. The ratings were performed against a scenario that included traffic officials' intentions to simplify the sign system. One dimension was amount of reduction in frequency of occurrence; subjects indicated percentages of reduction they believed to be reasonable. A second dimension was appropriateness of complete elimination of a sign from the traffic environment; subjects rated the degree to which elimination was reasonable. Subjective frequency of sign occurrence was rated last. Construct validation procedures showed strong correlations between reduction and elimination ratings only for the higher-experience group. Contrary to expectation, both groups showed the same high level of positive attitudes toward all signs. As expected, frequency was a judgmental base for utility, though weakly, except for permissive signs. It was more extensively related to utility for the higher-experience group, particularly for percentage ratings. Curvilinear relationships obtained between frequency and utility for permissive and road guidance signs.