Ecological Interface Design and Head-Up Displays: The Contact-Analog Visualization Tradeoff.

OBJECTIVE: This study investigated how the visualization of an ecological interface affects its subjective and objective usefulness. Therefore, we compared a simple 2D visualization against a contact-analog 3D visualization. BACKGROUND: Recently, head-up displays (HUDs) have become contact-analog and visualizations have been enabled to be merged with the real environment. In this regard, ecological interface design visualizing boundaries of acceptable performance might be a perfect match. Because the real-world environment already provides such boundaries (e.g., lane markings), the interface might directly use them. However, visual illusions and undesired interference with the environment might influence the overall usability. METHOD: To allow for a comparison, 49 participants tested the same ecological interface in two configurations, contact-analog (3D) and two dimensional (2D). Both visualizations were shown in the car's head-up display (HUD). RESULTS: The driving simulator experiment reveals that 3D was rated as more demanding and more disturbing, but also more innovative and appealing. However, regarding driving performance, the 3D representation decreased the accuracy of speed control by 6% while significantly increasing lane stability by 20%. CONCLUSION: We conclude that, if we want environmental boundaries guiding our behavior, the indicator for the behavior should be visualized contact-analog. If we desire artificial boundaries (e.g., speed limits) to guide behavior, the behavioral indicator should be visualized in 2D. This is less prone to optical illusions and allows for a more precise control of behavior. APPLICATION: These findings provide guidance to human factors engineers, how contact-analog visualizations might be used optimally.

Task Interruption and Control Recovery Strategies After Take-Over Requests Emphasize Need for Measures of Situation Awareness.

OBJECTIVE: Our objective was to determine whether there is a need to go beyond measures of automation deactivation time to understand the transition to manual driving after take-over requests (TORs) using the example of office tasks as nondriving-related tasks (NDRTs). BACKGROUND: Office tasks are likely NDRTs during automated commutes to/from work. Complex tasks can influence how manual control and visual attention is recovered after TORs. METHOD: N = 51 participants in a driving simulator performed either one of two office tasks or no task (between subjects). We recorded reaction times in a high-urgency and low-urgency scenario (within subjects) and analyzed task interruption strategies. RESULTS: 90% of the participants who performed an NDRT deactivated the automation after 7 to 8 s. However, 90% of the same drivers looked at the side mirror for the first time only after 11 to 14 s. Drivers with office tasks either interrupted the tasks sequentially or in parallel. Strategies were not adapted to the take-over situation or the task but appeared to be due to individual preferences. CONCLUSION: Drivers engaged in NDRTs may neglect lower priority subtasks after a TOR, such as mirror checking. Therefore, there is a need to go beyond measures of automation deactivation time to understand the transition to manual driving. Using analyses of attentional dynamics during take-over situations may enhance the safety of future car-driver handover assistance systems. APPLICATION: If low driver availability is detected, TORs should only be used as a fallback option if sufficient time and adaptive driver support can be provided.

Prefer what you like? Evaluation and preference of cycling infrastructures in a bicycle simulator.

PROBLEM: Previous research on cyclists' route evaluations and preferences already identified influencing factors and relevant evaluation criteria, but studies mostly focused on selected aspects like safety or comfort. This study examined the evaluation of routes more comprehensively considering five evaluation criteria, and further aims to compare the evaluation with the preference of routes. For this, we used the experimental approach of a bicycle simulator. METHOD: Our participants cycled route segments that varied in certain route characteristics. Each segment was rated in total and on five criteria generated in a previous study, namely Mental Comfort, Interaction, Environment, Ease of Use, and Physical Comfort. At the end, all route segments were ranked according to their quality. RESULTS: Results showed that separated paths were rated the best, while busy footpaths and uphill segments were rated the worst. Interestingly, interacting with pedestrians was described to be more attention-demanding but not as mentally uncomfortable as interacting with motor traffic. The evaluation and preference of routes mostly went hand in hand but differed for the footpath, which was ranked better than it was rated. Results further indicated that gradient has such a strong impact on the physical comfort of a route that it even influenced the overall evaluation. DISCUSSION: Our findings suggest that the evaluation and preference of routes is influenced by the degree of separation, traffic volume, the type of the road user that the cyclists may need to interact with, but most importantly, it is influenced by the interaction of these three aspects. PRACTICAL IMPLICATIONS: The five criteria we used can reliably assess the evaluation and preference of routes. They help to differentiate the reason for negative evaluation of routes. This differentiation is crucial to improve cycling routes, as different causes for dissatisfaction among cyclists require different consequences.

Development and evaluation of passenger assistance system concepts to reduce passenger discomfort.

The front seat passenger is often neglected when developing support systems for cars. There exist few examples of systems that provide information or interaction possibilities specifically to those passengers. Previous research indicated that the passive role of the passenger can frequently lead to a feeling of discomfort, potentially caused by missing information and missing control with respect to the driving situation. This paper investigates if and how different aspects of cognitive processes as defined in a previously published model can be approached with a technical system to reduce discomfort in passengers. Five prototypical passenger assistance systems are created which provide missing information (for example about the attentiveness of the driver) or the possibility to have more influence as a passenger. In a static simulator study with N = 40 participants, these systems were investigated with respect to their influence on measures of discomfort. Participants experienced in a counterbalanced order car following and braking scenarios on the highway with different time headways (within-subjects), with and without one of the passenger assistance systems (between-subjects). Based on the subjective measures for each experienced situation, three systems were identified as particularly useful in reducing discomfort. These displayed the attentiveness of the driver, the safety distance to a vehicle in front or provided the possibility to signal the driver that the recent safety distance is too small. These best proposals significantly reduced passenger discomfort in the tested Following and Braking scenarios for different time headways. In the post inquiry, more than 64% of the passengers confirmed the helpfulness of the rated system in reducing their discomfort in each case and about 75% of the passengers reported an interest in using it in their vehicle. This demonstrates opportunities to improve the everyday driving experience beyond classical assistance systems by explicitly considering the needs of passengers.

Signal evaluation environment: a new method for the design of peripheral in-vehicle warning signals.

An evaluation method called the Signal Evaluation Environment (SEE) was developed for use in the early stages of the design process of peripheral warning signals while driving. Accident analyses have shown that with complex driving situations such as intersections, the visual scan strategies of the driver contribute to overlooking other road users who have the right of way. Salient peripheral warning signals could disrupt these strategies and direct drivers' attention towards these road users. To select effective warning signals, the SEE was developed as a laboratory task requiring visual-cognitive processes similar to those used at intersections. For validation of the SEE, four experiments were conducted using different stimulus characteristics (size, colour contrast, shape, flashing) that influence peripheral vision. The results confirm that the SEE is able to differentiate between the selected stimulus characteristics. The SEE is a useful initial tool for designing peripheral signals, allowing quick and efficient preselection of beneficial signals.

Situational influences on response time and maneuver choice: Development of time-critical scenarios.

Findings concerning drivers' response times to sudden events vary considerably across studies due to different experimental setups and situational characteristics, such as expectancy of an event and urgency to react. While response times are widely reported in the literature, understanding of drivers' choice of maneuvers in time-critical situations is limited. Standardized test scenarios could enhance the comparability of studies and help in attaining a better understanding of driver behavior in these situations. In an effort to achieve these improvements, three driving simulator studies (N = 131) were conducted to investigate drivers' response time and maneuver choice under a range of situational conditions. Each study took place in a specific environmental setting (urban, rural, and highway) and incorporated one unexpected and 12 subsequent events (increased expectancy). Four different time-critical scenarios were used to evoke different driver responses. In three scenarios, obstacles suddenly entered the roadway (braking, steering, or both possible). A fourth scenario comprised the sudden braking of a leading vehicle (only braking possible). Half of the drivers performed a cognitive secondary task. To validate the findings, results from an additional field test (N = 14) were compared to the results from the simulated urban environment. As expected, response choice was influenced by scenario characteristics (available braking distance and room for evasive maneuvers). Braking maneuvers were more frequent in settings with lower speed limits (urban) while steering maneuvers were found at higher speed limits (highway). Responses to suddenly appearing obstacles were fastest in the urban setting at 540-680 ms; these responses were 200-300 ms slower in the rural and highway settings. Response times increased by 100-200 ms when drivers responded to braking leading vehicles rather than obstacles. Braking responses were 200-350 ms slower and steering responses were 90-200 ms slower when drivers responded to an unexpected event rather than subsequent events. The cognitive secondary task had no significant effect. The simulated environment and the field test produced comparable response behavior. The current study provides reference numbers that help to establish a set of standardized test scenarios for future studies. On basis of this study, nine scenarios are recommended for the context of time-critical crash avoidance maneuvers. Such standardized test scenarios could improve the comparability of future studies on response time and maneuver choice.

Asleep at the automated wheel-Sleepiness and fatigue during highly automated driving.

Due to the lack of active involvement in the driving situation and due to monotonous driving environments drivers with automation may be prone to become fatigued faster than manual drivers (e.g. Schömig et al., 2015). However, little is known about the progression of fatigue during automated driving and its effects on the ability to take back manual control after a take-over request. In this driving simulator study with Nö=ö60 drivers we used a three factorial 2ö×ö2ö×ö12 mixed design to analyze the progression (12ö×ö5ömin; within subjects) of driver fatigue in drivers with automation compared to manual drivers (between subjects). Driver fatigue was induced as either mainly sleep related or mainly task related fatigue (between subjects). Additionally, we investigated the drivers' reactions to a take-over request in a critical driving scenario to gain insights into the ability of fatigued drivers to regain manual control and situation awareness after automated driving. Drivers in the automated driving condition exhibited facial indicators of fatigue after 15 to 35ömin of driving. Manual drivers only showed similar indicators of fatigue if they suffered from a lack of sleep and then only after a longer period of driving (approx. 40ömin). Several drivers in the automated condition closed their eyes for extended periods of time. In the driving with automation condition mean automation deactivation times after a take-over request were slower for a certain percentage (about 30%) of the drivers with a lack of sleep (Mö=ö3.2; SDö=ö2.1ös) compared to the reaction times after a long drive (Mö=ö2.4; SDö=ö0.9ös). Drivers with automation also took longer than manual drivers to first glance at the speed display after a take-over request and were more likely to stay behind a braking lead vehicle instead of overtaking it. Drivers are unable to stay alert during extended periods of automated driving without non-driving related tasks. Fatigued drivers could pose a serious hazard in complex take-over situations where situation awareness is required to prepare for threats. Driver fatigue monitoring or controllable distraction through non-driving tasks could be necessary to ensure alertness and availability during highly automated driving.

How to warn drivers in various safety-critical situations - Different strategies, different reactions.

Technological advances allow supporting drivers in a multitude of occasions, ranging from comfort enhancement to collision avoidance, for example through driver warnings, which are especially crucial for traffic safety. This psychological driving simulator experiment investigated how to warn drivers visually in order to prevent accidents in various safety-critical situations. Collision frequencies, driving behavior and subjective evaluations of situation criticality, warning understandability and helpfulness of sixty drivers were measured in two trials of eight scenarios each (within-subjects factors). The warning type in the head-up display (HUD) varied (between-subjects) in its strategy (attention-/reaction-oriented) and specificity (generic/specific) over four warning groups and a control group without a warning. The results show that the scenarios differed in their situation criticality and drivers adapted their reactions accordingly, which underlines the importance of testing driver assistance systems in diverse scenarios. Besides some learning effects over the trials, all warned drivers showed faster and stronger brake reactions. Some warning concepts were understood better than others, but all were accepted. Generic warnings were effective, yet the warning strategy should adapt to situation requirements and/or driver behavior. A stop symbol as reaction generic warning is recommendable for diverse kinds of use cases, leading to fast and strong reactions. However, for rather moderate driver reactions an attention generic approach with a caution symbol might be more suitable. Further research should investigate multi-stage warnings with adaptive strategies for application to various situations including other modalities and false alarms.

Practice makes better - Learning effects of driving with a multi-stage collision warning.

Advanced driver assistance systems like (forward) collision warnings can increase traffic safety. As safety-critical situations (especially in urban traffic) can be diverse, integrated adaptive systems (such as multi-stage warnings) need to be developed and examined in a variety of use cases over time instead of the more common approach of testing only one-time effectiveness in the most relevant use case. Thus, this driving simulator experiment investigated a multi-stage collision warning in partially repetitive trials (T) of various safety-critical situations (scenarios confronting drivers with hazards in form of pedestrians, obstacles or preceding vehicles). Its output adapted according to the drivers' behavior in two warning stages (W1 - warning for moderate deceleration in less critical situations; W2 - urgent warning for strong, fast braking in more critical situations). To analyze how much drivers benefit from the assistance when allowed practice with it, the driving behavior and subjective ratings of 24 participants were measured over four trials. They comprised a baseline without assistance (T1) and three further trials with assistance - a learning phase repeating the scenarios from T1 twice (T2 + T3) and a concluding transfer drive with new scenarios (T4). As expected, the situation criticality in the urgent warning (W2) scenarios was rated higher than in the warning (W1) scenarios. While the brake reaction time differed more between the W1 scenarios, the applied brake force differed more between the W2 scenarios. However, the scenario factor often interacted with the trial factor. Since in later warning stages reaction time reductions become finite, the reaction strength gains importance. Overall the drivers benefited from the assistance. Both warning stages led to faster brake reactions (of similar strength) in all three assisted trials compared to the baseline, which additionally improved successively over time (T1-T3, T1 vs. T4, T2 vs. T4). Moreover, the drivers applied the gained knowledge from the learning phase to various new situations (transfer: faster brake reactions in T4 compared to T1 or T2). The well accepted and positively rated (helpful and understandable) two-stage collision warning can thus be recommended as it facilitates accident mitigation by earlier decelerations. Practice with advanced driver assistance systems (even in driving simulators) should be endorsed to maximize their benefits for traffic safety and accident prevention.

Systematic review of observational studies on secondary task engagement while driving.

The last decade has seen a worldwide exponential increase in the use of mobile information systems, especially smartphones. This trend covers all areas of life, and also seems to include phone use while driving. In order to assess the scope of secondary task occupation, especially smartphone use while driving, observation studies from outside the car have been established as an efficient and valid method. A review of international studies using traffic observation was done finding 51 publications with a total of 117 observation studies with more than 1,800,000 single observations at more than 17,500 sites from nine different countries. The review describes the relevant aspects of the observation methods and gives an overview about the trends found in the data. As the methods differ widely over the years as well as between the countries and studies, an integration of the results is not possible. However, from all studies it is very clear that smartphone use has increased including not only phoning while driving but also, more important to traffic safety, using apps and texting on the smartphone. Additional observable secondary tasks were only rarely examined. Thus, further research using observational studies is strongly recommended. Suggestions are given with regard to the methodology which can contribute to get comparable and valid results across countries and studies.

When does alcohol hurt? A driving simulator study.

World-wide, alcohol is still a major cause of traffic accidents. The dose-related accident risk function has been found in a large number of risk studies. A plethora of laboratory studies has examined the effect of alcohol with regard to different information processing capabilities of drivers. Summarizing the results, alcohol effects occur at lower blood alcohol concentrations (BAC) the more complex the tasks get. However, in contrast, typical alcohol-related crashes are frequently single vehicle crashes but not so often crashes in complex situations like at intersections. It may be that the subjective assessment of the traffic situation and the adaptation of behavior under the influence of alcohol plays a major role in accident causation. In order to examine this hypothesis, two driving simulator studies were conducted at a target BAC of 0.5g/l comparing two (alcohol vs. placebo; n=48, Experiment 1) and three (sober, placebo and alcohol; n=63, Experiment 2) groups of subjects in two critical scenarios. The first scenario was a seemingly easy traffic situation and was supposed to lead to a relaxed driving behavior under alcohol. The second scenario involved a complex intersection situation where especially drivers under the influence of alcohol should try to concentrate and compensate their experienced alcohol effects. In all scenarios, a critical object appeared suddenly and the driver had to react fast in order to prevent a (simulated) accident. Overall, the results support the hypothesis. Accidents were more frequent for alcohol drivers as compared to placebo/sober drivers in the easy scenario, but not the complex one. The initial speed of the driver when entering the scenario seems to play a major role in the accident causation. Drivers under the influence of alcohol seem to lower their speed in complex scenarios, possibly to thus counteract alcohol effects. In seemingly easy scenarios this does not seem necessary for them and the arousing effect of alcohol may contribute to driving faster. The results are summarized in a model of alcohol-related crashes. Further in-depth analyses of real crashes would be an interesting next step to further corroborate this model.

Effect of chronic opioid therapy on actual driving performance in non-cancer pain patients.

RATIONALE: Chronic non-cancer pain (CNCP) is a major health problem. Patients are increasingly treated with chronic opioid therapy (COT). Several laboratory studies have demonstrated that long-term use of opioids does not generally impair driving related skills. But there is still a lack of studies investigating on-the-road driving performance in actual traffic. OBJECTIVES: The present study assessed the impact of COT on road-tracking and car-following performance in CNCP patients. METHODS: Twenty CNCP patients, long-term treated with stable doses of opioid analgesics, and 19 healthy controls conducted standardized on-the-road driving tests in normal traffic. Performance of controls with a blood alcohol concentration (BAC) of 0.5 g/L was used as a reference to define clinically relevant changes in driving performance. RESULTS: Standard Deviation of Lateral Position (SDLP), a measure of road-tracking control, was 2.57 cm greater in CNCP patients than in sober controls. This difference failed to reach statistical significance in a superiority test. Equivalence testing indicated that the 95% CI around the mean SDLP change was equivalent to the SDLP change seen in controls with a BAC of 0.5 g/L and did not include zero. When corrected for age differences between groups the 95% CI widened to include both the alcohol reference criterion and zero. No difference was found in car-following performance. CONCLUSIONS: Driving performance of CNCP patients did not significantly differ from that of controls due to large inter-individual variations. Hence in clinical practice determination of fitness to drive of CNCP patients who receive opioid treatments should be based on an individual assessment.

Do German drivers use their smartphones safely?-Not really!

Research in the laboratory as well as in naturalistic driving studies has shown that texting while driving seems to be the most dangerous driver distraction. However, there is still some discussion about the extent to which drivers adapt their behavior to the traffic situation. Accordingly, they might use their phones only in easy driving situations but refrain from doing so when driving becomes more demanding. For Germany, no reliable data on these topics could be found although overall smartphone use has also increased exponentially in this country. As observational studies have proven to be an effective means to gather these data, such a study was done observing 11,837 drivers in three big German cities (Braunschweig, Hannover, Berlin) during daytime. An alarmingly high rate of texting while driving was found (4.5%) as compared to other international studies. This was even more frequent than the use of handheld (2.2%) and hands-free (1.7%) phones combined. Thus, there seems to be a special problem in Germany with texting which should be further examined as this activity is highly distracting. Finally, there was some indication that drivers adapt their secondary task activities to the requirements of the driving task (e.g. somewhat less texting when moving than when stationary at a red traffic light). However, these adaptations were not very strong. Thus, drivers seem to underestimate the dangers due to distraction. This could be a starting point for countermeasures which increase this awareness of danger.

How the presence of passengers influences the risk of a collision with another vehicle.

The risk of a collision with another vehicle due to the presence of passengers is analysed in detail in a large sample of accidents from Mittelfranken, Germany, from the years 1984 to 1997. Using a responsibility analysis, the overall effect of the presence of passengers and the influence of modifying variables is examined. While a general protective effect of the presence of passengers is found, this is reduced in young drivers, during darkness, in slow traffic and at crossroads, especially when disregarding the right of way and passing a car. These findings are interpreted as a general positive effect of the presence of passengers who influence the driver's behaviour towards more cautious and thus safer driving behaviour. However, passengers may also distract drivers' attention in an amount which cannot be compensated for in all situations and by all drivers by cautious driving. Besides educational measure, a potential solution to this problem may be driver assistance systems which give an adapted kind of support when passengers are present.

Perfect timing: urgency, not driving situations, influence the best timing to activate warnings.

OBJECTIVE: The aim of the study was to investigate the influence of different driving scenarios (urban, rural, highway) on the timing required by drivers from a two-stage warning system, based on car-to-car communication. BACKGROUND: Car-to-car communication systems are designed to inform drivers of potential hazards at an early stage, before they are visible to them. Here, questions arise as to how drivers acknowledge early warnings and when they should be informed (first stage) and warned (second stage). Hence, optimum timing for presenting the information was tested. METHOD: A psychophysical method was used to establish the optimum timing in three driving scenarios at different speed limits (urban: 50 km/h, rural: 100 km/h, highway: 130 km/h). A total of 24 participants (11 female, 13 male; M = 29.1 years, SD = 11.6 years) participated in the study. RESULTS: The results showed that the optimum timing did not differ among the three scenarios.The first and second stages should ultimately be presented at different timings at each speed limit (first stage: 26.5 s, second stage: 12.1 s before a potential hazard). CONCLUSION: The results showed that well-selected timing for activating information and warning is crucial for the acceptance of these systems. Appropriate timing for presenting the information and warning can be derived for these systems. APPLICATION: The findings will be integrated in further development of assistance systems based on car-to-x technology within the Car2X-Safety project of the Niedersächsisches Forschungszentrum Fahrzeugtechnik in Germany.This study was also supported by Chalmers University of Technology in Sweden.

How to present collision warnings at intersections?--a comparison of different approaches.

Analyses of intersection accidents have shown that in most cases drivers overlook or see other road users with the right of way too late that they cannot react in time. Appropriate visual warning signals which support drivers in their attention allocation and driving behavior could be useful to improve drivers' reaction. In a driving simulator study, two warning strategies varying in their timing: (1) top-down warning while approaching a critical intersection and (2) bottom-up warning directly before the critical incident were investigated in a T-intersection situation. For the bottom-up warning, two warning signal designs were compared. 48 subjects (M=27.3 years, SD=7.4 years) participated in the study. Driving data as well as subjective evaluation of the three warning signals (one early and two late warning signals) were analyzed. The early warning signal which was given while approaching the intersection showed a positive effect. Here, most collisions could be avoided due to drivers' adaptation of their driving behavior toward safer driving. They waited longer at the intersection before turning and finally turned with a lower velocity. In addition, drivers evaluated the early warning signal as very "useful". With regard to the late warnings a much smaller effect was found. From these results, requirements can be derived for the design of effective warning strategies when driving at critical intersections.

Improving the driver-automation interaction: an approach using automation uncertainty.

OBJECTIVE: The aim of this study was to evaluate whether communicating automation uncertainty improves the driver-automation interaction. BACKGROUND: A false system understanding of infallibility may provoke automation misuse and can lead to severe consequences in case of automation failure. The presentation of automation uncertainty may prevent this false system understanding and, as was shown by previous studies, may have numerous benefits. Few studies, however, have clearly shown the potential of communicating uncertainty information in driving. The current study fills this gap. METHOD: We conducted a driving simulator experiment, varying the presented uncertainty information between participants (no uncertainty information vs. uncertainty information) and the automation reliability (high vs.low) within participants. Participants interacted with a highly automated driving system while engaging in secondary tasks and were required to cooperate with the automation to drive safely. RESULTS: Quantile regressions and multilevel modeling showed that the presentation of uncertainty information increases the time to collision in the case of automation failure. Furthermore, the data indicated improved situation awareness and better knowledge of fallibility for the experimental group. Consequently, the automation with the uncertainty symbol received higher trust ratings and increased acceptance. CONCLUSION: The presentation of automation uncertaintythrough a symbol improves overall driver-automation cooperation. APPLICATION: Most automated systems in driving could benefit from displaying reliability information. This display might improve the acceptance of fallible systems and further enhances driver-automation cooperation.

Learning the Lane Change Task: comparing different training regimes in semi-paced and continuous secondary tasks.

For road safety it is paramount that distraction by in-vehicle systems is limited. To reach this aim the Lane Change Task (LCT; Mattes, 2003) was developed. It is used as a test procedure to measure distraction due to secondary tasks in driving. The LCT is implemented as an ISO standard (ISO 26022: 2010) with the aim to provide an objective criterion for designing human-machine interactions (HMI) in a way which is not detrimental to driving. As different baseline performance in the LCT could not be sufficiently explained in recent studies, comparisons of different training regimes were conducted in order to examine training influences on LCT performance. Discriminable performance improvements in LCT were found depending on the secondary task used. A training regime of at least ten runs of LCT in single-task mode is recommended for effective training. This training should be supplemented by a training of the secondary tasks examined. An additional exploration of a dual-task situation is recommended.

What does the driver look at? The influence of intersection characteristics on attention allocation and driving behavior.

One of the main contributing factors with intersection accidents is lack of information due to attention allocation. In many cases, drivers fail to yield right of way to other traffic participants. One reason is that drivers have inappropriate expectations about a traffic situation. They allocate their attention primarily to certain areas of the intersection but neglect others. In a driving simulator study, the influence of intersection complexity on drivers' expectations and their driving behavior was examined. In two T-intersections, the complexity was varied by the traffic density (low and high) using either one or two important objects: vehicles (left) with or without pedestrians (right). Additionally, the reaction to two critical incidents in close proximity of the intersections was examined. Gaze behavior, vehicle reactions, and subjective data were recorded. 40 subjects (26 male, 14 female, M=31.0 years, SD=11.9 years) participated in the study. Interestingly, the least complex intersections showed the most accidents which was interpreted as the result of inadequate attention allocation. It was shown that both the drivers' attention allocation and vehicle velocity when turning off were responsible for this effect. The results contribute to a better understanding of the role of drivers' expectation and attention allocation in the causation of intersection accidents.

Driving with a partially autonomous forward collision warning system: how do drivers react?

OBJECTIVE: The effects of a forward collision warning (FCW) and braking system (FCW+) were examined in a driving simulator study analyzing driving and gaze behavior and the engagement in a secondary task. BACKGROUND: In-depth accident analyses indicate that a lack of appropriate expectations for possible critical situations and visual distraction may be the major causes of rear-end crashes. Studies with FCW systems have shown that a warning alone was not enough for a driver to be able to avoid the accident. Thus,an additional braking intervention by such systems could be necessary. METHOD: In a driving simulator experiment, 30 drivers took part in a car-following scenario in an urban area. It was assumed that different lead car behaviors and environmental aspects would lead to different drivers' expectations of the future traffic situation. Driving with and without FCW+ was introduced as a between-subjects factor. RESULTS: Driving with FCW+ resulted in significantly fewer accidents in critical situations. This result was achieved by the system's earlier reaction time as compared with that of drivers. The analysis of the gaze behavior showed that driving with the system did not lead to a stronger involvement in secondary tasks. CONCLUSION: The study supports the hypotheses about the importance of missing expectations for the occurrence of accidents. These accidents can be prevented by an FCW+ that brakes autonomously. APPLICATION: The results indicate that an autonomous braking intervention should be implemented in FCW systems to increase the effectiveness of these assistance systems.