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Evaluation of vibrotactile feedback for forward collision warning on the steering wheel and seatbelt
International Journal of Industrial Ergonomics 42 (2012) 443e448
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International Journal of Industrial Ergonomics journal homepage: www.elsevier.com/locate/ergon
Evaluation of vibrotactile feedback for forward collision warning on the steering wheel and seatbelt Jaemin Chun a, Sung H. Han a, *, Gunhyuk Park b, Jongman Seo b, In lee b, Seungmoon Choi b a b
Department of Industrial & Management Engineering, Pohang University of Science and Technology (POSTECH), San 31, Hyoja, Pohang, South Korea Department of Computer Science and Engineering, Pohang University of Science and Technology (POSTECH), San 31, Hyoja, Pohang, South Korea
a r t i c l e i n f o
a b s t r a c t
Article history: Received 22 February 2012 Received in revised form 10 July 2012 Accepted 15 July 2012 Available online 4 August 2012
This study evaluated the efficacy of haptic feedback for Forward Collision Warning (FCW). Haptic FCW using vibrotactile feedback was delivered to the participants through a steering wheel or a seatbelt when the participants could possibly divert their visual attention from the road. In addition, we provided a no warning scenario as the control condition. A virtual driving simulator implementing the visually distracted driving situation and forward collision scenarios was developed. A visually distracted driving situation was simulated by having participants perform a text-entry task while they were following a preceding car. Participants in two age groups (30e40 years old and 50e60 years old) were recruited to define an age effect. The reaction time (RT) to the haptic FCW and the collision prevention rate (CPR) were used as performance measures while the participants’ perception on the usefulness of the haptic warnings and their overall satisfaction with the system were used as preference measures. The results show that participants had shorter RT and higher CPR with haptic warnings. The interaction between the haptic warning types and the age was significant to the CPR. The younger group showed lower CPR than the older group in the control condition, higher CPR with the haptic steering wheel, and similar CPR with the haptic seatbelt. Similar to the performance measures, the preference measure results demonstrate that the participants of both age groups felt the haptic FCWs were useful and satisfactory. We conclude that the haptic steering wheel and the haptic seatbelt could be effectively used as forward collision warnings. Relevance to industry: This study evaluates the effectiveness of haptic warning signals on a steering wheel and a seatbelt for FCW. The effect of the haptic warnings was evaluated by conducting an experiment using a driving simulator and the specifications of the warnings tested are laid out in this paper. The result of this study could be used for developing a haptic FCW by automobile manufacturers. Ó 2012 Elsevier B.V. All rights reserved.
Keywords: Automobile Vehicle Haptic Warning Forward Collision Warning (FCW)
1. Introduction A driving environment has become more complex with advanced electronic devices and drivers tend to lose their visual attention from the road while receiving information from those devices (Bendak and Al-Saleh, 2010; Lin et al., 2010). A comprehensive study on driver’s behavior reported that drivers conduct more than 30 additional tasks that require visual attention while driving (Klauer et al., 2010). Moreover, drivers engage in some of those tasks (such as adjusting the radio, looking at objects in/out of vehicle and talking on a cell phone) more than 1000 times a year. Those secondary tasks frequently come with other risky situations such as decreased driving performance, no hands on the steering wheel, lane departure and inattention to the road (Stutts et al., * Corresponding author. Tel.: þ82 54 279 2203; fax: þ82 54 279 2920. E-mail addresses: [email protected], [email protected] (S.H. Han). 0169-8141/$ e see front matter Ó 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.ergon.2012.07.004
2005). Especially when a driver is focusing on an object with a narrow visual angle, accident risks could increase (Tang et al., 2006). Thus, an effective warning could be helpful for attracting attention of distracted drivers when they are unable to detect possible collision situations. To this end, forward collision warnings in the form of a visual or auditory feedback were introduced in several studies (Lee et al., 1997; Lind, 2007; Perez et al., 2009). However, visual warnings have a risk of not being noticed by drivers when they are distracted (Ho et al., 2005) and the auditory warnings could be masked and not be delivered to the driver because of the ambient noise (Ryu et al., 2010). Moreover, a recent study revealed that a cross-modal effect called the “inattentional deafness” exists between the visual and auditory senses (Macdonard and Lavie, 2011). In their study, 79% of the participants in a high-visual-load condition failed to notice an auditory stimulus. As the driving task requires high visual workload (Shinar and Schieber, 1991), such “inattentional
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deafness” can affect drivers and reduce the effectiveness of auditory warnings. A haptic feedback, on the other hand, has several advantages over visual and auditory feedback. Because haptic feedback uses a different sensory channel, it does not increase the workload of the visual or auditory modalities which are already busy when driving. Haptic feedback also has additional benefits associated with cognitive processes compared to visual or auditory sensory channels. In most cases, haptic feedback is transferred through a direct contact and delivered directly from the haptic feedback generator to the driver. Such direct interaction enables information to be delivered only to the driver, who actually needs the warnings. In a number of recent studies (Carlander et al., 2007; Mohebbi et al., 2009; Scott and Gray, 2008), drivers showed better performance in terms of reaction time when a stimulus was given by tactile sensation rather than through visual or auditory sensory channels. Recently, collision warnings using haptic feedback have been introduced by industries and research institutions. Some automobile manufacturers have developed haptic warning systems on the steering wheel, seats and pedals. Studies were conducted to evaluate the effectiveness of haptic warning systems and to develop guidelines for applying haptic feedback as warning signals. Ho et al. (2006) examined the effectiveness of haptic feedback on a driver’s waist and back for FCW. Fitch (2008) assessed the ability of haptic warning to alert distracted drivers and Stanley (2006) estimated the steering performance and the level of annoyance with haptic feedback on the seat. Similarly, the effectiveness of a haptic Lane Departure Warning (LDW) with torque feedback on the steering wheel was evaluated (Griffiths and Gillespie, 2005). By integrating the evaluation results of such studies, the NHTSA (National Highway Traffic Safety Administration) rated the efficacy of various haptic warning displays (such as brake pulse, accelerator counterforce, accelerator vibration, steering wheel torque, steering wheel vibration, and seat shaker) for FCW (Campbell et al., 2007). For example, haptic FCWs on pedals (brake and accelerator) were rated as ‘Poor’ to ‘Fair’ because driver’s foot may not always be on those pedals. As such, steering wheel torque and vibration were rated as ‘poor’ and seat shaker was rated as ‘Fair’ to ‘Good’. However, it is difficult to generalize some of the ratings because they are derived from limited studies. More specifically, Campbell et al. (2007) rated the steering wheel vibration as ‘poor’ based on the studies of Tijerina et al. (1996, 2000). However, as mentioned in the studies of Tijerina et al. (1996, 2000), the vibrotactile feedback used in their studies (steering wheel vibrated for 0.5e2.0 s with square wave at 10 Hz and 1e1.5 Nm) was too weak to attract driver’s attention. In fact, the problem was the specification of the vibrotactile feedback, not the way it was delivered. We expected that more intense vibrotactile feedback can increase the efficacy of a steering wheel vibration as a warning. In addition, as the steering wheel is located in front of the drivers and since the drivers usually hold the steering wheel throughout driving, we expected that providing a haptic FCW on the steering wheel might be effective and natural for the drivers. Thus, we decided to redefine the efficacy of a steering wheel vibration. A new type of haptic warning system using a commercial seatbelt with a pre tensioner was also considered. In this study, experiments using human subjects were conducted to evaluate the efficacy of haptic feedback on the steering wheel and seatbelt for FCW. The participants drove a driving simulator while performing a text-entry task designed to distract them. FCW events were provided to the participants to see if the provided haptic FCWs were helpful while avoiding the collision risks. To assess the age effect, participants in two different age bands (30e40 years and 50e60 years) were considered.
2. Driving simulator A virtual driving environment and a FCW situation were simulated in a driving simulation system equipped with hardware devices and a software program. As for the hardware part, a sitting buck of the actual size and the layout of a vehicle were built (Fig. 2). The sitting buck consisted of a steering wheel, accelerator, brake pedals (G25 Racing Wheel; Logitech, USA), driving seat, vibration actuators attached on the steering wheel, and a vibrotactile feedback seatbelt (Pre-safe Seatbelt; Hyundai Motor company, Korea) (Fig. 1). Here, participants were able to adjust the distance and angle of the sitting buck to their comfortable position. Driver’s forward and side visions were presented on three displays. To provide a more immersive driving environment, we also took a different focus distance of forward and side visions into consideration by displaying the forward vision on a 50-inch PDP TV and the side visions on two 23-inch LCD monitors. The angles and locations of the three displays were calibrated to provide seamless visual surroundings from the participant’s viewpoint (Fig. 1). For the secondary task to be performed by the participants, a 7-inch UMPC (Ultra Mobile Personal Computer) with a touch screen (S130, Kohjinsha) was provided (Fig. 1). As for the software program, we developed a program to simulate the virtual driving environment using an open-source game engine, Irrlicht (version 1.5). The virtual environment consisted of a 3.5 m wide one-way straight road, a driver’s car, and a car preceding the driver’s car. Each car had a footprint of 4.9 (L) 1.9 (W) m. Performance measures (RT and CPR) were automatically collected by the software program. Vibrotactile feedback was generated by six coin-type ERM (Eccentric Rotating Mass) vibration motors (Fig. 2). Three vibration motors were attached on each side (left and right) of the steering wheel. All six vibration motors generated identical amplitudemodulated sinusoidal vibrations. The base carrier sinusoidal signal had 100 Hz frequency and 0.025 mm amplitude when sending 4 V rectangular pulses to the vibration motors. Its envelope was turned on and off periodically with 0.4 s on-time and 0.1 s offtime. The specification of vibration was determined by pilot tests and the vibration provided during the actual test had sufficient intensity (above the detection threshold), allowing participants to detect warnings immediately (Morioka and Griffin, 2005). The haptic seatbelt was Hyundai Motor’s commercial “pre-safe seatbelt system.” When a possible collision situation was detected, vibrotactile feedback was generated by tightening itself for 0.5 s and then vibrated for 2.0 s with a frequency of 10 Hz. When tightened, a pressure of 30e35 N was also given on the driver’s shoulder and chest (Fig. 2).
Fig. 1. Displays of driving simulator and secondary task device.
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Fig. 2. Driving simulator and haptic FCWs.
A training session was provided to the participants so that they can become familiar with the driving simulator and haptic FCWs. When haptic FCW was provided, participants had to wear both ear plugs and headphones to block the sound cue that could have been produced from the vibration actuators. A white noise in a wide frequency band was played through the headphones to block the sound cue produced by vibration motors. 3. Methods 3.1. Participants Younger (30e40 years old) and older (50e60 years old) age groups were considered in this study. Each age group included 12 male participants with a driver’s license. The average age of the younger group was 39.3 (s.d. ¼ 7.3) while that of the older group was 56.0 (s.d. ¼ 5.3). The average length of driving experience was 14.2 years (s.d. ¼ 7.5) for the younger group and 19.1 years (s.d. ¼ 4.3) for the older group. 3.2. Experimental design The experiment employed a two-factor mixed design. The age group (younger and older) was a between-subjects factor while the haptic warning type (none, steering wheel and seatbelt) was a within-subjects factor. Combining the age group factor with the haptic warning type factor yielded six experimental conditions. Several performance and preference measures were collected as dependent variables. To measure performance, RT and the CPR were collected. In this study, we defined the RT as the elapsed time between the points of a preceding vehicle’s deceleration (with brake lights on) and the participant’s manipulation of the brake pedal. The CPR was computed by dividing the number of successful decelerations (without collision) by the total number of collision events. As for preference measures, participants were asked after the experiment to score the level of usefulness of the provided collision warning and their overall satisfaction. To give a clear warning signal to participants, we provided intense vibrotactile stimuli. Even if the haptic FCWs were successfully delivered to participants, they may have felt uncomfortable or annoyed by the haptic FCWs and thus considered them to be less useful. To this end, we asked the participants to rate the usefulness of the haptic FCWs after the experiment. The participants were also asked to consider any inconvenience or discomfort they may have felt from the warnings when evaluating the overall satisfaction. A large difference in individual satisfaction scores can indicate subjectivity in the acceptability of the haptic warning technology, regardless of its perceived usefulness. Since the haptic warning system was new to participants, we also asked the initial impression they got when they were first
exposed to the haptic warnings. In addition, to observe any interesting reactions or behaviors of the participants, the entire procedure of the experiment was videotaped. 3.3. Experimental task and procedure A dual task paradigm was used in the experiment. The primary task of the participants was to follow a vehicle in front of them, which was at a constant speed of 80 km/h. While they successfully followed the preceding car by maintaining less than 40 m distance between the two cars, the experimental program issued a text message on the screen, asking the participants to conduct a secondary task. To distract the participants, we chose a text-entry task as the secondary task (Fig. 1). The participants were asked to enter a seven-digit number presented on a touch screen using a numeric keypad which took about 10 s in the pilot test. When the participants were conducting the primary and the secondary tasks simultaneously, their visual attention switched back and forth constantly between the preceding vehicle and the display. Whenever the participants made an input error, we thought that the participants were not distracted by the secondary task while conducting the primary task and no FCW event was provided. While the participants successfully performed the secondary task, sudden forward collision events were created by the software program. The preceding car suddenly decelerated to a rate of 12 km/s2, so the participants had to slow down to avoid forward collision. These events were generated with a probability of 50%. Otherwise, the participants might have predicted the timing of the collision event easily. The forward collision event was repeated 20 times for each experimental condition. The haptic FCW was activated when TTC (Time to Collision) was below 4 s. In other words, haptic FCW was provided 4 s prior to an expected collision and continued until TTC reached back to 4 s. When a participant failed to decelerate and hit the preceding car, the experimental program simulated the impact of collision by shaking the images presented on the simulator displays. 4. Results An analysis of variance (ANOVA) was used to determine the statistical significance of the experimental factors (the age group and the type of haptic warning) and their interaction (a ¼ 0.05). Differences between significant factors were analyzed using the Student-NewmaneKeuls (SNK) test and simple effect tests were conducted for significant interactions. 4.1. Reaction time (RT) The average RT of the participants is shown in Fig. 3. The mean RT decreased from 1.75 s to 1.48 s with the haptic steering wheel
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Fig. 3. The reaction time (Bars in each subfigure marked with the same letter are not significantly different from each other; SNK test, a ¼ 0.05).
Fig. 4. The collision prevention rate (Bars in each subfigure marked with the same letter are not significantly different from each other; SNK test, a ¼ 0.05).
and to 1.54 s with the haptic seatbelt. This effect was statistically significant for both haptic warning types (F2,44 ¼ 10.15, p < 0.001). In other words, the haptic FCWs led to a reduction in braking distance, which was 6.13 m less with the haptic steering wheel and 4.73 m less with the haptic seatbelt. The age factor also had a significant influence on the RT (F1,22 ¼ 4.30, p ¼ 0.049). Regardless of the warning type, the younger group (1.48 s) reacted 0.22 s faster than the older group (1.70 s). Note that the interaction effect between haptic FCW types and age was not significant.
a sudden deceleration of the preceding car, they stepped on the brake pedal after a collision. The haptic FCWs gave participants a better chance to detect a potential collision risk and to manipulate the brake pedal before a crash. The video analysis showed that the participants stepped on the brake pedal as soon as they received a haptic warning signal, which resulted in the decreased RT. A fast reaction to the haptic FCW is also associated with the characteristics of human perception. Generally, the reaction time to a haptic stimulus is known to be shorter than those to other sensory channels. Scott and Gray (2008) found that when a haptic feedback was used to warn about a rear-end collision, the reaction time was shorter than that of a visual or auditory signal. In the study by Burke et al. (2006), a multimodal warning signal (visualetactile and visualeauditory feedback) shortened the driver’s reaction time to a greater level when compared to a warning signal that used visual feedback only. Several studies also demonstrated that a haptic warning with directional information is very effective in terms of reducing the reaction time compared to other modalities (Carlander et al., 2007; Santangelo and Spence, 2007).
4.2. Collision prevention rate (CPR) The CPR was significantly affected by haptic warnings (F2,44 ¼ 16.58, p < 0.001) and by interaction between haptic FCW types and age (F2,44 ¼ 4.12, p < 0.023). The haptic steering wheel increased the CPR from 0.17 to 0.42, while the CPR reached 0.33 with the haptic seatbelt (Fig. 4). As shown in the simple effect analysis, with the haptic steering wheel, the younger group was able to avoid collisions much better than the older group (Fig. 5). However, no significant age difference was observed in the CPR with the haptic seatbelt. 4.3. Preference measures The effects of haptic FCW types on participant’s perceived usefulness and overall satisfaction were significant (F2,44 ¼ 47.93, p < 0.001 and F2,66 ¼ 28.07, p < 0.001, respectively). Regardless of the age group, both the perceived usefulness and the overall satisfaction increased when haptic FCWs were provided (Fig. 6). All age groups had similar preference measures (Table 1). 5. Discussion 5.1. Effect of haptic FCWs on RT The experiment clearly verified the improvement in the RT when haptic FCWs were provided (Fig. 3). When the participants were distracted by the secondary task and unable to detect
Fig. 5. The collision prevention rate (Points within the same ellipse are not significantly different; simple effects test, a ¼ 0.05).
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Fig. 6. The perceived usefulness and the overall satisfaction (Bars in each subfigure marked with the same letter are not significantly different from each other; SNK test, a ¼ 0.05).
5.2. Effect of age on RT In general, the simple reaction time to a stimulus shows little difference between the ages of 15e60 and displays moderate slowing after 60 (Keele, 1986). However, with a task that requires a high cognitive load, the reaction time increases with age (Luchies et al., 2002; Der and Deary, 2006). Because the participants in our study were asked to perform the complicated experimental tasks (monitoring the status of the preceding car, maintaining a constant speed and distance, entering numbers), the older group had a longer RT than the younger group. 5.3. Effect of haptic FCWs on CPR Similar to the results of the RT, the haptic FCWs helped the participants to avoid collision events more successfully (Fig. 4). The participants showed higher CPR with the haptic steering wheel than the haptic seatbelt. Through the video analysis, we identified a typical behavior that people engage in while manipulating the brake pedal and found the reason of CPR difference between the haptic FCWs. When a FCW event was provided, the participants bent their body forward and transferred their body weight to their feet in order to step on the brake pedal strongly. However, as the “pre-safe seatbelt system” pulled the participants torso by repeatedly tightening and loosening the seatbelt to produce the haptic warning, it could have limited the participants’ natural operation of the brake pedal and thus resulted in a decrement of CPR. Comments from some participants also reflected this side effect of the haptic seatbelt; 8 participants of the younger group felt the haptic seatbelt was uncomfortable (such as stiff and disturbing), while only one participant reported discomfort with the haptic steering wheel.
Overall satisfaction
Younger group
Older group
Younger group
Older group
6. Conclusion
31.67 82.08 77.50
50.83 85.21 80.17
34.58 80.25 74.00
56.25 82.67 83.08
Interestingly, in the absence of the haptic FCW, the CPR of the older group was significantly higher than the younger group (Fig. 5). The older drivers compensated for declining perception and Table 1 Preference measures.
No warning Steering wheel Seatbelt
5.5. Effects of haptic FCWs and age on preference measures Regardless of the age group, the participants gave higher evaluations to the haptic FCWs than to the non-haptic condition (Fig. 6). Since the participants performed better with the haptic FCWs, their preferences for the non-haptic condition could have been dropped radically after experiencing haptic FCWs. More specifically, the younger group gave lower scores to the non-haptic condition than the older group (Table 1). Considering the difference in driving habits between age groups, such as older drivers being more careful when driving, the younger drivers could have perceived haptic FCWs to be more effective than the older people. The similar scores of the usefulness and the overall satisfaction (Table 1) indicate that although some participants may felt discomfort with haptic FCWs (such as the rough feeling they got from the vibration actuator), their negative effects were not significant for either age group. User observation and short interview showed that the participants felt surprised and strange at first regarding the haptic FCW. However, after a few trials, they became familiar with the stimulus and their level of discomfort greatly decreased. Nevertheless, to provide a better tactile vibration, the design specification of the vibration feedback can be modified. For instance, by combining a higher vibration frequency and amplitude, smoother but sufficiently strong enough (stronger than the detection threshold) vibration feedback can be generated.
5.4. Effect of age on CPR
Warning type
motor skills with greater driving experience and a tendency to drive slower (Green, 2009). Similarly, in our experiment, the participants of the older group drove too slowly and failed to trigger the FCW events. These habits resulted in a higher CPR of the older group than the younger group. As shown in Fig. 5, when the haptic steering wheel was used, the younger group had a higher CPR than the older group, which is similar to the result of the RT (Fig. 3). On the other hand, even though the RT of haptic FCWs (1.37 s for the haptic steering wheel and 1.38 s for the haptic seatbelt) was almost the same in the younger group, the CPR of the haptic seatbelt was lower than that of the haptic steering wheel. We found the reason of the low CPR with the haptic seatbelt from the younger participants’ comments. Nearly half of them felt an intense discomfort (such as stiffness or inconvenience, surprise or confusion) with the haptic seatbelt and such discomfort could have interrupted the cognitive process of warning detection.
Usefulness
We evaluated the effect of vibrotactile feedback on the steering wheel and the seatbelt for FCW. Haptic FCWs significantly
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decreased the RT and increased the CPR. The participants showed a better performance with the haptic steering wheel than the haptic seatbelt. The performance of the younger group was generally higher than that of the older group. The younger group took a greater advantage of haptic feedback due to their superior motor skills and sensitivity to haptic sensation. The preference measures, similar to the performance measures, showed that the participants considered the haptic FCWs to be useful and were satisfied with them. Moreover, the participants quickly understood the meaning of the haptic FCWs and soon became familiar with them. Based on the results of this study, we conclude that the vibrotactile feedback on the steering wheel and the seatbelt can be effectively used as FCW. Nevertheless, further research is necessary to make generalization about the effectiveness of the proposed haptic warning system. With further research, robust specifications of vibrotactile feedback could be found for aged and female drivers by considering their cognitive and affective characteristics. Moreover, to provide a timely collision warning, driver behavior and driving strategy need to be analyzed. Acknowledgment This work was supported by Mid-career Researcher Program through the National Research Foundation of Korea (NRF) grant funded by the Ministry of Education, Science and Technology (MEST) (No. 2010-0000364). References Bendak, S., Al-Saleh, K., 2010. The role of roadside advertising signs in distracting drivers. International Journal of Industrial Ergonomics 40 (3), 233e236. Burke, J.L., Prewett, M.S., Elliot, L.R., 2006. Comparing the effects of visual-auditory and visual-tactile feedback on user performance: a meta-analysis. In: Proceedings of the 8th International Conference on Multimodal Interfaces, pp. 108e117. New York, NY, USA. Campbell, J.L., Richard, C.M., Brown, J.L., McCallum, M., 2007. Crash Warning System Interfaces: Human Factors Insights and Lessons Learned. National Highway Traffic Safety Administration (NHTSA). Carlander, O., Eriksson, L., Oskarsson, P.A., 2007. Handling uni- and multimodal threat cueing with simultaneous radio calls in a combat vehicle setting. Lecture Notes on Computer Science (UAHCI’07) 4555, 293e302. Der, G., Deary, I.J., 2006. Age and sex differences in reaction time in adulthood: results from the United Kingdom Health and Lifestyle Survey. Psychology and Aging 21 (1), 62e73. Fitch, G.M., 2008. Driver Comprehension of Integrated Collision Avoidance System Alerts Presented through a Haptic Driver Seat. Ph. D. dissertation. Industrial and Systems Engineering, Virginia Polytechnic Institute and State University. Green, M., 2009. Driver Reaction Time [Online] Available: http://www.visualexpert. com/Resources/reactiontime.html.
Griffiths, P.G., Gillespie, R.B., 2005. Sharing control between humans and automation using haptic interface: primary and secondary task performance benefits. Human Factors 47 (3), 574e590. Ho, C., Reed, N., Spence, C., 2006. Assessing the effectiveness of “intuitive” vibrotactile warning signals in preventing front-to-rear-end collisions in a driving simulator. Accident Analysis and Prevention 38 (5), 988e996. Ho, C., Spence, C., Tan, H., 2005. Warning signals go multisensory. In: Proceedings of the 11th Annual Conference on HumaneComputer Interaction, pp. 22e27. Keele, S.W., 1986. Motor control. In: Boff, J.K., Kaufman, L., Thomas, J.P. (Eds.), Handbook of Human Perception and Performance, vol. 2. Wiley, New York. Klauer, S.G., Guo, F., Sudweeks, J., Dingus, T.A., 2010. An Analysis of Driver Inattention Using a Case-crossover Approach on 100-car Data. National Highway Traffic Safety Administration (NHTSA). Lee, J., McGehee, D.V., Dingus, T.A., Wilson, T., 1997. Collision Avoidance Behavior of Unalerted Drivers Using a Front-to-rear-end Collision Warning Display on the Iowa Driving Simulator. Technical report, Transportation Research Record, National Research Council. Lin, C., Wu, H., Chien, T., 2010. Effects of e-map format and sub-windows on driving performance and glance behavior when using an in-vehicle navigation system. International Journal of Industrial Ergonomics 40 (3), 330e336. Lind, H., 2007. An Efficient Visual Forward Collision Warning Display for Vehicles. SAE World Congress, Detroit, USA. Luchies, C.W., Schiffman, J., Richards, L.G., Thompson, M.R., Bazuin, D., DeYoung, A.J., 2002. Effects of age, step direction, and reaction condition on the ability to step quickly. The Journals of Gerontology: Series A 57 (4), 246e249. Macdonard, J.S.P., Lavie, N., 2011. Visual perceptual load induces inattentional deafness. Attention, Perception, & Psychophysics 73 (6), 1780e1789. Mohebbi, R., Gray, R., Tan, H.Z., 2009. Driver reaction time to tactile and auditory rear-end collision warnings while talking on a cell phone. Human Factors 51 (1), 102e110. Morioka, M., Griffin, M.J., 2005. Thresholds for the perception of hand-transmitted vibration: dependence on contact area and contact location. Somatosensory & Motor Research 22 (4), 281e297. Perez, M., Kiefer, R., Haskins, A., Hankey, J., 2009. Evaluation of forward collision warning system visual alert candidates and SAE J2400. SAE International Journal of Passenger Cars e Mechanical Systems 2 (1), 750e764. Ryu, J., Chun, J., Park, G., Choi, S., Han, S.H., 2010. Vibrotactile feedback for information delivery in the vehicle. IEEE Transactions on Haptics 1 (2), 138e149. Santangelo, V., Spence, C., 2007. Assessing the automaticity of the exogenous orienting of tactile attention. Perception 36 (10), 1497e1505. Scott, J.J., Gray, R., 2008. A comparison of tactile, visual, and auditory warnings for rear-end collision prevention in simulated driving. Human Factors 50 (2), 264e275. Shinar, D., Schieber, F., 1991. Visual requirements for safety and mobility of older drivers. Human Factors 33 (5), 507e519. Stanley, L.M., 2006. Haptic and auditory cues for lane departure warnings. Proceedings of the Human Factors and Ergonomics Society Annual Meeting 50 (22), 2405e2408. Stutts, J., Feaganes, J., Reinfurt, D., Rodgman, E., Hamlett, C., Gish, K., Staplin, L., 2005. Driver’s exposure to distractions in their natural driving environment. Accident Analysis and Prevention 37 (6), 1093e1101. Tang, K.H., Tsai, L.C., Lee, Y.H., 2006. A human factors study on a modified stop lamp for motorcycles. International Journal of Industrial Ergonomics 36 (6), 533e540. Tijerina, L., Jackson, J., Pomerleau, D., Romano, R., Petersen, A., 1996. Driving simulator tests of lane departure collision avoidance system. In: Proceedings of ITS America Sixth Annual Meeting, pp. 636e648. Houston, TX. Tijerina, L., Johnston, S., Parmer, E., Pham, H.A., Winterbottom, M.D., 2000. Preliminary Studies in Haptic Displays for Rear-end Collision Avoidance System and Adaptive Cruise Control System Applications. National Highway Traffic Safety Administration (NHTSA).
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International Journal of Industrial Ergonomics journal homepage: www.elsevier.com/locate/ergon
Evaluation of vibrotactile feedback for forward collision warning on the steering wheel and seatbelt Jaemin Chun a, Sung H. Han a, *, Gunhyuk Park b, Jongman Seo b, In lee b, Seungmoon Choi b a b
Department of Industrial & Management Engineering, Pohang University of Science and Technology (POSTECH), San 31, Hyoja, Pohang, South Korea Department of Computer Science and Engineering, Pohang University of Science and Technology (POSTECH), San 31, Hyoja, Pohang, South Korea
a r t i c l e i n f o
a b s t r a c t
Article history: Received 22 February 2012 Received in revised form 10 July 2012 Accepted 15 July 2012 Available online 4 August 2012
This study evaluated the efficacy of haptic feedback for Forward Collision Warning (FCW). Haptic FCW using vibrotactile feedback was delivered to the participants through a steering wheel or a seatbelt when the participants could possibly divert their visual attention from the road. In addition, we provided a no warning scenario as the control condition. A virtual driving simulator implementing the visually distracted driving situation and forward collision scenarios was developed. A visually distracted driving situation was simulated by having participants perform a text-entry task while they were following a preceding car. Participants in two age groups (30e40 years old and 50e60 years old) were recruited to define an age effect. The reaction time (RT) to the haptic FCW and the collision prevention rate (CPR) were used as performance measures while the participants’ perception on the usefulness of the haptic warnings and their overall satisfaction with the system were used as preference measures. The results show that participants had shorter RT and higher CPR with haptic warnings. The interaction between the haptic warning types and the age was significant to the CPR. The younger group showed lower CPR than the older group in the control condition, higher CPR with the haptic steering wheel, and similar CPR with the haptic seatbelt. Similar to the performance measures, the preference measure results demonstrate that the participants of both age groups felt the haptic FCWs were useful and satisfactory. We conclude that the haptic steering wheel and the haptic seatbelt could be effectively used as forward collision warnings. Relevance to industry: This study evaluates the effectiveness of haptic warning signals on a steering wheel and a seatbelt for FCW. The effect of the haptic warnings was evaluated by conducting an experiment using a driving simulator and the specifications of the warnings tested are laid out in this paper. The result of this study could be used for developing a haptic FCW by automobile manufacturers. Ó 2012 Elsevier B.V. All rights reserved.
Keywords: Automobile Vehicle Haptic Warning Forward Collision Warning (FCW)
1. Introduction A driving environment has become more complex with advanced electronic devices and drivers tend to lose their visual attention from the road while receiving information from those devices (Bendak and Al-Saleh, 2010; Lin et al., 2010). A comprehensive study on driver’s behavior reported that drivers conduct more than 30 additional tasks that require visual attention while driving (Klauer et al., 2010). Moreover, drivers engage in some of those tasks (such as adjusting the radio, looking at objects in/out of vehicle and talking on a cell phone) more than 1000 times a year. Those secondary tasks frequently come with other risky situations such as decreased driving performance, no hands on the steering wheel, lane departure and inattention to the road (Stutts et al., * Corresponding author. Tel.: þ82 54 279 2203; fax: þ82 54 279 2920. E-mail addresses: [email protected], [email protected] (S.H. Han). 0169-8141/$ e see front matter Ó 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.ergon.2012.07.004
2005). Especially when a driver is focusing on an object with a narrow visual angle, accident risks could increase (Tang et al., 2006). Thus, an effective warning could be helpful for attracting attention of distracted drivers when they are unable to detect possible collision situations. To this end, forward collision warnings in the form of a visual or auditory feedback were introduced in several studies (Lee et al., 1997; Lind, 2007; Perez et al., 2009). However, visual warnings have a risk of not being noticed by drivers when they are distracted (Ho et al., 2005) and the auditory warnings could be masked and not be delivered to the driver because of the ambient noise (Ryu et al., 2010). Moreover, a recent study revealed that a cross-modal effect called the “inattentional deafness” exists between the visual and auditory senses (Macdonard and Lavie, 2011). In their study, 79% of the participants in a high-visual-load condition failed to notice an auditory stimulus. As the driving task requires high visual workload (Shinar and Schieber, 1991), such “inattentional
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deafness” can affect drivers and reduce the effectiveness of auditory warnings. A haptic feedback, on the other hand, has several advantages over visual and auditory feedback. Because haptic feedback uses a different sensory channel, it does not increase the workload of the visual or auditory modalities which are already busy when driving. Haptic feedback also has additional benefits associated with cognitive processes compared to visual or auditory sensory channels. In most cases, haptic feedback is transferred through a direct contact and delivered directly from the haptic feedback generator to the driver. Such direct interaction enables information to be delivered only to the driver, who actually needs the warnings. In a number of recent studies (Carlander et al., 2007; Mohebbi et al., 2009; Scott and Gray, 2008), drivers showed better performance in terms of reaction time when a stimulus was given by tactile sensation rather than through visual or auditory sensory channels. Recently, collision warnings using haptic feedback have been introduced by industries and research institutions. Some automobile manufacturers have developed haptic warning systems on the steering wheel, seats and pedals. Studies were conducted to evaluate the effectiveness of haptic warning systems and to develop guidelines for applying haptic feedback as warning signals. Ho et al. (2006) examined the effectiveness of haptic feedback on a driver’s waist and back for FCW. Fitch (2008) assessed the ability of haptic warning to alert distracted drivers and Stanley (2006) estimated the steering performance and the level of annoyance with haptic feedback on the seat. Similarly, the effectiveness of a haptic Lane Departure Warning (LDW) with torque feedback on the steering wheel was evaluated (Griffiths and Gillespie, 2005). By integrating the evaluation results of such studies, the NHTSA (National Highway Traffic Safety Administration) rated the efficacy of various haptic warning displays (such as brake pulse, accelerator counterforce, accelerator vibration, steering wheel torque, steering wheel vibration, and seat shaker) for FCW (Campbell et al., 2007). For example, haptic FCWs on pedals (brake and accelerator) were rated as ‘Poor’ to ‘Fair’ because driver’s foot may not always be on those pedals. As such, steering wheel torque and vibration were rated as ‘poor’ and seat shaker was rated as ‘Fair’ to ‘Good’. However, it is difficult to generalize some of the ratings because they are derived from limited studies. More specifically, Campbell et al. (2007) rated the steering wheel vibration as ‘poor’ based on the studies of Tijerina et al. (1996, 2000). However, as mentioned in the studies of Tijerina et al. (1996, 2000), the vibrotactile feedback used in their studies (steering wheel vibrated for 0.5e2.0 s with square wave at 10 Hz and 1e1.5 Nm) was too weak to attract driver’s attention. In fact, the problem was the specification of the vibrotactile feedback, not the way it was delivered. We expected that more intense vibrotactile feedback can increase the efficacy of a steering wheel vibration as a warning. In addition, as the steering wheel is located in front of the drivers and since the drivers usually hold the steering wheel throughout driving, we expected that providing a haptic FCW on the steering wheel might be effective and natural for the drivers. Thus, we decided to redefine the efficacy of a steering wheel vibration. A new type of haptic warning system using a commercial seatbelt with a pre tensioner was also considered. In this study, experiments using human subjects were conducted to evaluate the efficacy of haptic feedback on the steering wheel and seatbelt for FCW. The participants drove a driving simulator while performing a text-entry task designed to distract them. FCW events were provided to the participants to see if the provided haptic FCWs were helpful while avoiding the collision risks. To assess the age effect, participants in two different age bands (30e40 years and 50e60 years) were considered.
2. Driving simulator A virtual driving environment and a FCW situation were simulated in a driving simulation system equipped with hardware devices and a software program. As for the hardware part, a sitting buck of the actual size and the layout of a vehicle were built (Fig. 2). The sitting buck consisted of a steering wheel, accelerator, brake pedals (G25 Racing Wheel; Logitech, USA), driving seat, vibration actuators attached on the steering wheel, and a vibrotactile feedback seatbelt (Pre-safe Seatbelt; Hyundai Motor company, Korea) (Fig. 1). Here, participants were able to adjust the distance and angle of the sitting buck to their comfortable position. Driver’s forward and side visions were presented on three displays. To provide a more immersive driving environment, we also took a different focus distance of forward and side visions into consideration by displaying the forward vision on a 50-inch PDP TV and the side visions on two 23-inch LCD monitors. The angles and locations of the three displays were calibrated to provide seamless visual surroundings from the participant’s viewpoint (Fig. 1). For the secondary task to be performed by the participants, a 7-inch UMPC (Ultra Mobile Personal Computer) with a touch screen (S130, Kohjinsha) was provided (Fig. 1). As for the software program, we developed a program to simulate the virtual driving environment using an open-source game engine, Irrlicht (version 1.5). The virtual environment consisted of a 3.5 m wide one-way straight road, a driver’s car, and a car preceding the driver’s car. Each car had a footprint of 4.9 (L) 1.9 (W) m. Performance measures (RT and CPR) were automatically collected by the software program. Vibrotactile feedback was generated by six coin-type ERM (Eccentric Rotating Mass) vibration motors (Fig. 2). Three vibration motors were attached on each side (left and right) of the steering wheel. All six vibration motors generated identical amplitudemodulated sinusoidal vibrations. The base carrier sinusoidal signal had 100 Hz frequency and 0.025 mm amplitude when sending 4 V rectangular pulses to the vibration motors. Its envelope was turned on and off periodically with 0.4 s on-time and 0.1 s offtime. The specification of vibration was determined by pilot tests and the vibration provided during the actual test had sufficient intensity (above the detection threshold), allowing participants to detect warnings immediately (Morioka and Griffin, 2005). The haptic seatbelt was Hyundai Motor’s commercial “pre-safe seatbelt system.” When a possible collision situation was detected, vibrotactile feedback was generated by tightening itself for 0.5 s and then vibrated for 2.0 s with a frequency of 10 Hz. When tightened, a pressure of 30e35 N was also given on the driver’s shoulder and chest (Fig. 2).
Fig. 1. Displays of driving simulator and secondary task device.
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Fig. 2. Driving simulator and haptic FCWs.
A training session was provided to the participants so that they can become familiar with the driving simulator and haptic FCWs. When haptic FCW was provided, participants had to wear both ear plugs and headphones to block the sound cue that could have been produced from the vibration actuators. A white noise in a wide frequency band was played through the headphones to block the sound cue produced by vibration motors. 3. Methods 3.1. Participants Younger (30e40 years old) and older (50e60 years old) age groups were considered in this study. Each age group included 12 male participants with a driver’s license. The average age of the younger group was 39.3 (s.d. ¼ 7.3) while that of the older group was 56.0 (s.d. ¼ 5.3). The average length of driving experience was 14.2 years (s.d. ¼ 7.5) for the younger group and 19.1 years (s.d. ¼ 4.3) for the older group. 3.2. Experimental design The experiment employed a two-factor mixed design. The age group (younger and older) was a between-subjects factor while the haptic warning type (none, steering wheel and seatbelt) was a within-subjects factor. Combining the age group factor with the haptic warning type factor yielded six experimental conditions. Several performance and preference measures were collected as dependent variables. To measure performance, RT and the CPR were collected. In this study, we defined the RT as the elapsed time between the points of a preceding vehicle’s deceleration (with brake lights on) and the participant’s manipulation of the brake pedal. The CPR was computed by dividing the number of successful decelerations (without collision) by the total number of collision events. As for preference measures, participants were asked after the experiment to score the level of usefulness of the provided collision warning and their overall satisfaction. To give a clear warning signal to participants, we provided intense vibrotactile stimuli. Even if the haptic FCWs were successfully delivered to participants, they may have felt uncomfortable or annoyed by the haptic FCWs and thus considered them to be less useful. To this end, we asked the participants to rate the usefulness of the haptic FCWs after the experiment. The participants were also asked to consider any inconvenience or discomfort they may have felt from the warnings when evaluating the overall satisfaction. A large difference in individual satisfaction scores can indicate subjectivity in the acceptability of the haptic warning technology, regardless of its perceived usefulness. Since the haptic warning system was new to participants, we also asked the initial impression they got when they were first
exposed to the haptic warnings. In addition, to observe any interesting reactions or behaviors of the participants, the entire procedure of the experiment was videotaped. 3.3. Experimental task and procedure A dual task paradigm was used in the experiment. The primary task of the participants was to follow a vehicle in front of them, which was at a constant speed of 80 km/h. While they successfully followed the preceding car by maintaining less than 40 m distance between the two cars, the experimental program issued a text message on the screen, asking the participants to conduct a secondary task. To distract the participants, we chose a text-entry task as the secondary task (Fig. 1). The participants were asked to enter a seven-digit number presented on a touch screen using a numeric keypad which took about 10 s in the pilot test. When the participants were conducting the primary and the secondary tasks simultaneously, their visual attention switched back and forth constantly between the preceding vehicle and the display. Whenever the participants made an input error, we thought that the participants were not distracted by the secondary task while conducting the primary task and no FCW event was provided. While the participants successfully performed the secondary task, sudden forward collision events were created by the software program. The preceding car suddenly decelerated to a rate of 12 km/s2, so the participants had to slow down to avoid forward collision. These events were generated with a probability of 50%. Otherwise, the participants might have predicted the timing of the collision event easily. The forward collision event was repeated 20 times for each experimental condition. The haptic FCW was activated when TTC (Time to Collision) was below 4 s. In other words, haptic FCW was provided 4 s prior to an expected collision and continued until TTC reached back to 4 s. When a participant failed to decelerate and hit the preceding car, the experimental program simulated the impact of collision by shaking the images presented on the simulator displays. 4. Results An analysis of variance (ANOVA) was used to determine the statistical significance of the experimental factors (the age group and the type of haptic warning) and their interaction (a ¼ 0.05). Differences between significant factors were analyzed using the Student-NewmaneKeuls (SNK) test and simple effect tests were conducted for significant interactions. 4.1. Reaction time (RT) The average RT of the participants is shown in Fig. 3. The mean RT decreased from 1.75 s to 1.48 s with the haptic steering wheel
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Fig. 3. The reaction time (Bars in each subfigure marked with the same letter are not significantly different from each other; SNK test, a ¼ 0.05).
Fig. 4. The collision prevention rate (Bars in each subfigure marked with the same letter are not significantly different from each other; SNK test, a ¼ 0.05).
and to 1.54 s with the haptic seatbelt. This effect was statistically significant for both haptic warning types (F2,44 ¼ 10.15, p < 0.001). In other words, the haptic FCWs led to a reduction in braking distance, which was 6.13 m less with the haptic steering wheel and 4.73 m less with the haptic seatbelt. The age factor also had a significant influence on the RT (F1,22 ¼ 4.30, p ¼ 0.049). Regardless of the warning type, the younger group (1.48 s) reacted 0.22 s faster than the older group (1.70 s). Note that the interaction effect between haptic FCW types and age was not significant.
a sudden deceleration of the preceding car, they stepped on the brake pedal after a collision. The haptic FCWs gave participants a better chance to detect a potential collision risk and to manipulate the brake pedal before a crash. The video analysis showed that the participants stepped on the brake pedal as soon as they received a haptic warning signal, which resulted in the decreased RT. A fast reaction to the haptic FCW is also associated with the characteristics of human perception. Generally, the reaction time to a haptic stimulus is known to be shorter than those to other sensory channels. Scott and Gray (2008) found that when a haptic feedback was used to warn about a rear-end collision, the reaction time was shorter than that of a visual or auditory signal. In the study by Burke et al. (2006), a multimodal warning signal (visualetactile and visualeauditory feedback) shortened the driver’s reaction time to a greater level when compared to a warning signal that used visual feedback only. Several studies also demonstrated that a haptic warning with directional information is very effective in terms of reducing the reaction time compared to other modalities (Carlander et al., 2007; Santangelo and Spence, 2007).
4.2. Collision prevention rate (CPR) The CPR was significantly affected by haptic warnings (F2,44 ¼ 16.58, p < 0.001) and by interaction between haptic FCW types and age (F2,44 ¼ 4.12, p < 0.023). The haptic steering wheel increased the CPR from 0.17 to 0.42, while the CPR reached 0.33 with the haptic seatbelt (Fig. 4). As shown in the simple effect analysis, with the haptic steering wheel, the younger group was able to avoid collisions much better than the older group (Fig. 5). However, no significant age difference was observed in the CPR with the haptic seatbelt. 4.3. Preference measures The effects of haptic FCW types on participant’s perceived usefulness and overall satisfaction were significant (F2,44 ¼ 47.93, p < 0.001 and F2,66 ¼ 28.07, p < 0.001, respectively). Regardless of the age group, both the perceived usefulness and the overall satisfaction increased when haptic FCWs were provided (Fig. 6). All age groups had similar preference measures (Table 1). 5. Discussion 5.1. Effect of haptic FCWs on RT The experiment clearly verified the improvement in the RT when haptic FCWs were provided (Fig. 3). When the participants were distracted by the secondary task and unable to detect
Fig. 5. The collision prevention rate (Points within the same ellipse are not significantly different; simple effects test, a ¼ 0.05).
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Fig. 6. The perceived usefulness and the overall satisfaction (Bars in each subfigure marked with the same letter are not significantly different from each other; SNK test, a ¼ 0.05).
5.2. Effect of age on RT In general, the simple reaction time to a stimulus shows little difference between the ages of 15e60 and displays moderate slowing after 60 (Keele, 1986). However, with a task that requires a high cognitive load, the reaction time increases with age (Luchies et al., 2002; Der and Deary, 2006). Because the participants in our study were asked to perform the complicated experimental tasks (monitoring the status of the preceding car, maintaining a constant speed and distance, entering numbers), the older group had a longer RT than the younger group. 5.3. Effect of haptic FCWs on CPR Similar to the results of the RT, the haptic FCWs helped the participants to avoid collision events more successfully (Fig. 4). The participants showed higher CPR with the haptic steering wheel than the haptic seatbelt. Through the video analysis, we identified a typical behavior that people engage in while manipulating the brake pedal and found the reason of CPR difference between the haptic FCWs. When a FCW event was provided, the participants bent their body forward and transferred their body weight to their feet in order to step on the brake pedal strongly. However, as the “pre-safe seatbelt system” pulled the participants torso by repeatedly tightening and loosening the seatbelt to produce the haptic warning, it could have limited the participants’ natural operation of the brake pedal and thus resulted in a decrement of CPR. Comments from some participants also reflected this side effect of the haptic seatbelt; 8 participants of the younger group felt the haptic seatbelt was uncomfortable (such as stiff and disturbing), while only one participant reported discomfort with the haptic steering wheel.
Overall satisfaction
Younger group
Older group
Younger group
Older group
6. Conclusion
31.67 82.08 77.50
50.83 85.21 80.17
34.58 80.25 74.00
56.25 82.67 83.08
Interestingly, in the absence of the haptic FCW, the CPR of the older group was significantly higher than the younger group (Fig. 5). The older drivers compensated for declining perception and Table 1 Preference measures.
No warning Steering wheel Seatbelt
5.5. Effects of haptic FCWs and age on preference measures Regardless of the age group, the participants gave higher evaluations to the haptic FCWs than to the non-haptic condition (Fig. 6). Since the participants performed better with the haptic FCWs, their preferences for the non-haptic condition could have been dropped radically after experiencing haptic FCWs. More specifically, the younger group gave lower scores to the non-haptic condition than the older group (Table 1). Considering the difference in driving habits between age groups, such as older drivers being more careful when driving, the younger drivers could have perceived haptic FCWs to be more effective than the older people. The similar scores of the usefulness and the overall satisfaction (Table 1) indicate that although some participants may felt discomfort with haptic FCWs (such as the rough feeling they got from the vibration actuator), their negative effects were not significant for either age group. User observation and short interview showed that the participants felt surprised and strange at first regarding the haptic FCW. However, after a few trials, they became familiar with the stimulus and their level of discomfort greatly decreased. Nevertheless, to provide a better tactile vibration, the design specification of the vibration feedback can be modified. For instance, by combining a higher vibration frequency and amplitude, smoother but sufficiently strong enough (stronger than the detection threshold) vibration feedback can be generated.
5.4. Effect of age on CPR
Warning type
motor skills with greater driving experience and a tendency to drive slower (Green, 2009). Similarly, in our experiment, the participants of the older group drove too slowly and failed to trigger the FCW events. These habits resulted in a higher CPR of the older group than the younger group. As shown in Fig. 5, when the haptic steering wheel was used, the younger group had a higher CPR than the older group, which is similar to the result of the RT (Fig. 3). On the other hand, even though the RT of haptic FCWs (1.37 s for the haptic steering wheel and 1.38 s for the haptic seatbelt) was almost the same in the younger group, the CPR of the haptic seatbelt was lower than that of the haptic steering wheel. We found the reason of the low CPR with the haptic seatbelt from the younger participants’ comments. Nearly half of them felt an intense discomfort (such as stiffness or inconvenience, surprise or confusion) with the haptic seatbelt and such discomfort could have interrupted the cognitive process of warning detection.
Usefulness
We evaluated the effect of vibrotactile feedback on the steering wheel and the seatbelt for FCW. Haptic FCWs significantly
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decreased the RT and increased the CPR. The participants showed a better performance with the haptic steering wheel than the haptic seatbelt. The performance of the younger group was generally higher than that of the older group. The younger group took a greater advantage of haptic feedback due to their superior motor skills and sensitivity to haptic sensation. The preference measures, similar to the performance measures, showed that the participants considered the haptic FCWs to be useful and were satisfied with them. Moreover, the participants quickly understood the meaning of the haptic FCWs and soon became familiar with them. Based on the results of this study, we conclude that the vibrotactile feedback on the steering wheel and the seatbelt can be effectively used as FCW. Nevertheless, further research is necessary to make generalization about the effectiveness of the proposed haptic warning system. With further research, robust specifications of vibrotactile feedback could be found for aged and female drivers by considering their cognitive and affective characteristics. Moreover, to provide a timely collision warning, driver behavior and driving strategy need to be analyzed. Acknowledgment This work was supported by Mid-career Researcher Program through the National Research Foundation of Korea (NRF) grant funded by the Ministry of Education, Science and Technology (MEST) (No. 2010-0000364). References Bendak, S., Al-Saleh, K., 2010. The role of roadside advertising signs in distracting drivers. International Journal of Industrial Ergonomics 40 (3), 233e236. Burke, J.L., Prewett, M.S., Elliot, L.R., 2006. Comparing the effects of visual-auditory and visual-tactile feedback on user performance: a meta-analysis. In: Proceedings of the 8th International Conference on Multimodal Interfaces, pp. 108e117. New York, NY, USA. Campbell, J.L., Richard, C.M., Brown, J.L., McCallum, M., 2007. Crash Warning System Interfaces: Human Factors Insights and Lessons Learned. National Highway Traffic Safety Administration (NHTSA). Carlander, O., Eriksson, L., Oskarsson, P.A., 2007. Handling uni- and multimodal threat cueing with simultaneous radio calls in a combat vehicle setting. Lecture Notes on Computer Science (UAHCI’07) 4555, 293e302. Der, G., Deary, I.J., 2006. Age and sex differences in reaction time in adulthood: results from the United Kingdom Health and Lifestyle Survey. Psychology and Aging 21 (1), 62e73. Fitch, G.M., 2008. Driver Comprehension of Integrated Collision Avoidance System Alerts Presented through a Haptic Driver Seat. Ph. D. dissertation. Industrial and Systems Engineering, Virginia Polytechnic Institute and State University. Green, M., 2009. Driver Reaction Time [Online] Available: http://www.visualexpert. com/Resources/reactiontime.html.
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