Driver sensitivity to brake pulse duration and magnitude

Benefits estimation of regenerative braking versus service braking

A central question not yet examined in the literature is whether regenerative braking provides a kinematic deceleration safety advantage in time and distance over traditional service braking. This research explores three conditions of braking (traditional service braking, low level of regenerative braking, and high level of regenerative braking) to determine any safety advantages regenerative braking offers. Thirty participants took part in a simulator study with a between-subjects study design, allocating 10 participants per condition. The study drive took place in a simulator and involved three braking events. The results showed a significant difference between the means of the three conditions for average deceleration of the vehicle in the time interval between the driver releasing the accelerator and pressing the brake for all three events showing RB did provide the drivers with a braking advantage. When events 1 and 2 were combined, there was also significance with maximum brake force. Practitioner summary: This research looked to determine whether regenerative braking provides a deceleration safety advantage over traditional service braking. The results showed RB did provide the drivers with a braking advantage. The results also showed driver foot behaviour differed with the RB High condition.

Catch My Drift: Elevating Situation Awareness for Highly Automated Driving with an Explanatory Windshield Display User Interface

Broad access to automated cars (ACs) that can reliably and unconditionally drive in all environments is still some years away. Urban areas pose a particular challenge to ACs, since even perfectly reliable systems may be forced to execute sudden reactive driving maneuvers in hard-to-predict hazardous situations. This may negatively surprise the driver, possibly causing discomfort, anxiety or loss of trust, which might be a risk for the acceptance of the technology in general. To counter this, we suggest an explanatory windshield display interface with augmented reality (AR) elements to support driver situation awareness (SA). It provides the driver with information about the car’s perceptive capabilities and driving decisions. We created a prototype in a human-centered approach and implemented the interface in a mixed-reality driving simulation. We conducted a user study to assess its influence on driver SA. We collected objective SA scores and self-ratings, both of which yielded a significant improvement with our interface in good (medium effect) and in bad (large effect) visibility conditions. We conclude that explanatory AR interfaces could be a viable measure against unwarranted driver discomfort and loss of trust in critical urban situations by elevating SA.

Emergency braking is affected by the use of cruise control

OBJECTIVE

We compared the differences in the braking response to vehicle collision between an active human emergency braking (control condition) and cruise control (CC) or adaptive cruise control (ACC).

METHODS

In 11 male subjects, age 22 to 67 years, we measured the active emergency braking response during manual driving using the accelerator pedal (control condition) or in condition mimicking CC or ACC. In both conditions, we measured the brake reaction time (BRT), delay to produce the peak braking force (PBD), total emergency braking response (BRT + PBD), and peak braking force (PBF). Electromyograms of leg and thigh muscles were recorded during braking. The tonic vibratory response (TVR), Hoffman reflex (HR), and M-waves were recorded in leg muscles to explore the change in sensorimotor control.

RESULTS

No difference in PBF, TVR amplitude, HR latency, and H_max/M_max ratio were found between the control and CC/ACC conditions. On the other hand, BRT and PBD were significantly lengthened in the CC/ACC condition (240 ± 13 ms and 704 ± 70 ms, respectively) compared to control (183 ± 7 ms and 568 ± 36 ms, respectively). BRT increased with the age of participants and the driving experience shortened PBD and increased PBF.

CONCLUSIONS

In male subjects, driving in a CC/ACC condition significantly delays the active emergency braking response to vehicle collision. This could result from higher amplitude of leg motion in the CC/ACC condition and/or by the age-related changes in motor control. Car and truck drivers must take account of the significant increase in the braking distance in a CC/ACC condition.

Drivers anticipate lead-vehicle conflicts during automated longitudinal control: Sensory cues capture driver attention and promote appropriate and timely responses

Adaptive Cruise Control (ACC) has been shown to reduce the exposure to critical situations by maintaining a safe speed and headway. It has also been shown that drivers adapt their visual behavior in response to the driving task demand with ACC, anticipating an impending lead vehicle conflict by directing their eyes to the forward path before a situation becomes critical. The purpose of this paper is to identify the causes related to this anticipatory mechanism, by investigating drivers' visual behavior while driving with ACC when a potential critical situation is encountered, identified as a forward collision warning (FCW) onset (including false positive warnings). This paper discusses how sensory cues capture attention to the forward path in anticipation of the FCW onset. The analysis used the naturalistic database EuroFOT to examine visual behavior with respect to two manually-coded metrics, glance location and glance eccentricity, and then related the findings to vehicle data (such as speed, acceleration, and radar information). Three sensory cues (longitudinal deceleration, looming, and brake lights) were found to be relevant for capturing driver attention and increase glances to the forward path in anticipation of the threat; the deceleration cue seems to be dominant. The results also show that the FCW acts as an effective attention-orienting mechanism when no threat anticipation is present. These findings, relevant to the study of automation, provide additional information about drivers' response to potential lead-vehicle conflicts when longitudinal control is automated. Moreover, these results suggest that sensory cues are important for alerting drivers to an impending critical situation, allowing for a prompt reaction.

Tactile warning signals for in-vehicle systems

The last few years have seen growing interest in the design of tactile warning signals to direct driver attention to potentially dangerous road situations (e.g. an impending crash) so that they can initiate an avoidance maneuver in a timely manner. In this review, we highlight the potential uses of such warning signals for future collision warning systems and compare them with more traditional visual and auditory warnings. Basic tactile warning signals are capable of promoting driver alertness, which has been demonstrated to be beneficial for forward collision avoidance (when compared to a no warning baseline condition). However, beyond their basic alerting function, directional tactile warning signals are now increasingly being utilized to shift the attention of the driver toward locations of interest, and thus to further facilitate their speeded responses to potential collision events. Currently, many researchers are focusing their efforts on the development of meaningful (iconic) tactile warning signals. For instance, dynamic tactile warnings (varying in their intensity and/or location) can potentially be used to convey meaningful information to drivers. Finally, we highlight the future research that will be needed in order to explore how to present multiple directional warnings using dynamic tactile cues, thus forming an integrated collision avoidance system for future in-vehicle use.

Vibrotactile pedals: provision of haptic feedback to support economical driving

The use of haptic feedback is currently an underused modality in the driving environment, especially with respect to vehicle manufacturers. This exploratory study evaluates the effects of a vibrotactile (or haptic) accelerator pedal on car driving performance and perceived workload using a driving simulator. A stimulus was triggered when the driver exceeded a 50% throttle threshold, past which is deemed excessive for economical driving. Results showed significant decreases in mean acceleration values, and maximum and excess throttle use when the haptic pedal was active as compared to a baseline condition. As well as the positive changes to driver behaviour, subjective workload decreased when driving with the haptic pedal as compared to when drivers were simply asked to drive economically. The literature suggests that the haptic processing channel offers a largely untapped resource in the driving environment, and could provide information without overloading the other attentional resource pools used in driving.

PRACTITIONER SUMMARY

Overloaded or distracted drivers present a real safety danger to themselves and others. Providing driving-related feedback can improve performance but risks distracting them further; however, giving such information through the underused haptic processing channel can provide the driver with critical information without overloading the driver's visual channel.

Automated Driving: Human-Factors Issues and Design Solutions

The goal of this paper is to outline human-factors issues associated with automated driving, with a focus on car following. First, we review the challenges of having automated driving systems from a human-factors perspective. Next, we identify human-machine interaction needs for automated vehicles and propose some available solutions. Finally, we propose design requirements for Cooperative Adaptive Cruise Control.