and the late warning condition. The results indicate that the timing of a warning is important in the design of collision warning systems. Front-to-rear-end crashes ...
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Effect of Warning Timing on Collision Avoidance Behavior in a Stationary Lead Vehicle Scenario Daniel V. McGehee, Timothy L. Brown, John D. Lee, and Terry B. Wilson Warning timing and how drivers with and without forward collision warning (FCW) systems react when distracted at the moment a stationary vehicle is revealed directly ahead were investigated. The study was conducted using the Iowa Driving Simulator (IDS). The IDS was equipped with an FCW system that provided auditory warnings based on two warning criteria. A total of 30 subjects were split across three conditions—a baseline of 10 subjects (no warning display), and two warning conditions (early and late) with 10 subjects each. The two warning conditions differed by the duration of an a priori driver reaction component (1.5 and 1.0 s) in the warning algorithm. Drivers’ collision avoidance performance in the two warning conditions was compared with that in the baseline condition. Results indicated that the early warning condition showed significantly shorter accelerator release reaction times, fewer crashes, and less severe crashes than both the baseline condition and the late warning condition. The results indicate that the timing of a warning is important in the design of collision warning systems.
Front-to-rear-end crashes involving two or more vehicles currently represent approximately one-fourth of all collisions. Specifically, the National Safety Council reported that there were approximately 11.3 million motor vehicle crashes in 1996 (1), of which 2.7 million were rear-end crashes (about 23.8 percent of the total). According to the General Estimates System and the Fatal Analysis Reporting System, in 1992 there were approximately 1.4 million policereported (PR) rear-end crashes. Rear-end collisions constituted approximately 23 percent of all PR crashes but only about 4.7 percent of all fatalities. While many injuries and fatalities are caused by rear-end crashes, such crashes also cause approximately 157 million vehicle-hours of delay annually, which is approximately one-third of all crash-caused delays. Rear-end collisions can be placed into two main categories: status of the lead vehicle when the collision occurs, and cause of the crash. In 69.7% of all rear-end crashes, the lead vehicle is stopped; in the remaining 30.3% of crashes, the lead vehicle is moving at the time of collision (2). Regardless of the status of the lead vehicle at the time of collision, driver inattention is a major cause of this type of crash. Knipling et al. (3) estimated that inattention accounts for 64% of all PR rear-end crashes and that inattention associated with following a preceding vehicle too closely represents the cause of 14% of rearD. V. McGehee, Human Factors and Vehicle Safety Research Program, University of Iowa Public Policy Center, 227 South Quad, Iowa City, IA 52242-1192. T. L. Brown, Human Factors Laboratory, NADS & Simulation Center, University of Iowa, 2401 Oakdale Blvd., Iowa City, IA 52242-5003. J. D. Lee, Cognitive Systems Laboratory, Department of Mechanical and Industrial Engineering, University of Iowa, Iowa City, IA 52242. T. B. Wilson, Sensor Technologies and Systems, Inc., 7655 East Redfield Road, Suite 10, Scottsdale, AZ 85260.
end crashes. Although all drivers experience some level of inattention while driving (e.g., talking to passengers, daydreaming, adjusting in-vehicle controls, and extra-vehicle distractions), inattention during critical situations may mean drivers will not be able to respond quickly enough to avoid a collision. These statistics taken together indicate that crash situations where the lead vehicle is stopped and the driver is not attending to the roadway are an important focus of study. Because rear-end crashes account for such a large percentage of automobile collisions, and because inattention is the most frequent cause of these crashes, there has been considerable research into the possibility of alerting inattentive drivers to potential collision situations (3–9). Several strategies exist to aid the driver in avoiding collisions. These strategies differ in terms of degree of intervention. They vary from alerts that suggest subtle speed adjustments to those that initiate automatic emergency braking. Warning the driver about imminent collisions is a promising method for mitigating rear-end collisions (4, 6, 7, 10–15). With this type of system, the driver is warned when a situation is detected that requires immediate response to avoid a collision. The algorithm that triggers the imminent warning is a critical element in providing meaningful alerts. The algorithm must provide ample warning in dangerous situations without being a nuisance to the driver. To achieve this, the algorithm must trigger the warning far enough in advance that the driver has time to react and avoid striking another vehicle, but not trigger the warning in situations that do not pose a hazard. The problem is that the earlier a warning is provided, the less certain it is that the situation will actually require the driver to act to avoid a collision. Thus, the earlier a warning occurs, the greater the chance that it may be interpreted as a nuisance alarm and therefore desensitize the driver to future system warnings (16). A warning strategy that can avoid nuisance alarms may provide significant benefit to drivers. Even a system that could provide a modest decrease in overall reaction time of 0.5 s could reduce rear-end crashes by 62% (15). It is clear that a careful implementation of an appropriate forward collision warning (FCW) strategy could reduce the number and severity of rear-end crashes. The primary objective of this study was to investigate whether drivers operating vehicles equipped with an FCW system would, when a stationary lead vehicle was revealed, exhibit enhanced frontto-rear-end collision avoidance behavior relative to those driving without such a system. A secondary objective of this study was to explore whether the timing of the warning affects driver reaction and performance. If an FCW warning system could provide drivers with information to help them avoid collisions, drivers operating a vehicle equipped with such a system would experience fewer
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front-to-rear-end crashes, faster reaction times, and slower impact speeds than those who did not have similarly equipped vehicles.
METHODS Subjects Thirty subjects aged 18 to 24 split by gender participated in the study. All subjects were required to possess a valid driver’s license and to drive at least 4,830 km (3,000 mi) per year. They were paid $20 for their participation. Research participants were prescreened over the telephone for susceptibility to motion sickness or previous simulator experience (only drivers with no simulator experience were inducted into the study). Because the number of subjects chosen for the study was insufficient to examine performance differences by age and experience (as in previous simulator studies), it was decided that only young subjects (18 to 24 years old) would be included.
Experimental Design Subjects were divided into a 3 × 1 factorial design; collision warning conditions included the baseline, early warning, and late warning conditions. All variables were between-subject and balanced by gender.
Collision Warning Conditions The primary warning display was an auditory car horn icon. A secondary head-down headway display was mounted over the tachometer within the peripheral view of the driver, but this was not considered to be a factor in the warning because of the distracter task, which intentionally distracted the driver’s visual attention away from the roadway ahead. A baseline condition was used to determine whether the two collision warning types (early and late) affected drivers’ responses to scenarios representative of common rear-end crashes.
IOWA DRIVING SIMULATOR The Iowa Driving Simulator (IDS) uses computational dynamics, parallel computing, and image generation to create a highly realistic motion-based ground–vehicle simulator. A Harris Power-PC-based host computer was used to run the software required for the simulation. Textured graphics were projected onto a panoramic screen in front of and to the rear of the driver. In this configuration, three Barco multisynch projectors were used to project a 190°-by-40° forward field-of-view image, and one to project a 60° rear-view image. The visual scene was rendered with an Evans and Sutherland ESIG 2000 image generator. A large-payload, six-degrees-of-freedom motion base produced the motion cues experienced during typical driving. A fully instrumented Saturn cab was used.
Multiplexed Video Four multiplexed views of the driving situation were recorded on videotape for later analysis, as shown in Figure 1.
FIGURE 1
Multiplexed video view.
The view in the upper left quadrant (1) was taken from the driver’s interior rearview mirror and shows the driver’s face and all eye and head movements. Steering position was overlaid in degrees (positive numbers indicated the wheel turning right and negative numbers a turn to the left). The view in the upper right quadrant (2) was a forward view of the driving environment projected onto the forward screen. Driver speed in miles per hour was overlaid along with an indication of the initiation of the auditory warning. The view in the lower left quadrant (3) was of the driver’s feet, taken from under the dash. This view was designed to record the movement of the driver’s foot on and off the accelerator and brake pedal. Both feet were in view at all times. Brake pedal and accelerator pedal input (measured in percent depression) was overlaid. The view in the lower right quadrant (4) was of the visual display with an overlay indicating when the truck swerve occurred, the headway from the vehicle ahead in seconds, and the video frame number.
Warning Algorithm A stopping distance algorithm was used in this study, which initiated a warning based on measured variables. These were range, range-rate (relative speed), and deceleration of the lead vehicle. The algorithm has three free parameters (assumed following-vehicle deceleration, warning time delay, and permissible range) that govern the timing and make the warnings more or less conservative. The two deceleration terms—the deceleration of the host vehicle and the deceleration of the lead vehicle—can be considered modifiers of their respective velocity terms. The stopping distance algorithm used was as follows: WD =
V f2 V l2 − + Td Vf + R 2 αf 2 αl
where WD = warning distance compared with sensor range to the lead vehicle, Vf = following (participant) vehicle absolute speed (measured), αf = following (participant) vehicle deceleration (assigned), Vl = lead vehicle absolute speed (measured), αl = lead vehicle deceleration (measured), Td = warning time delay (assigned), and R = permissible range (assigned).
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WD was continuously calculated and compared with the measured headway between the host and lead vehicles. If the headway was less than the warning distance, a warning was initiated. The deceleration terms assume a constant deceleration by the driver. The deceleration term was selected to be equal to the maximum possible deceleration of the participant vehicle. For the purpose of the stationary lead vehicle study, the second term was zero (Vl = 0). The parameters used are as follows: Vf αf Td R
= = = =
participant vehicle speed (measured), 0.75 g (7.35 m/s2), 1.0 s (late) and 1.5 s (early), and 2 m.
For a nominal speed of 29 m/s (65 mph) the warning distances are 88 m for the late warning condition and 103 m for the early warning condition. The stopping distance algorithm functions to bring the host vehicle to a stop at a distance of R (2 m) behind the lead vehicle when the driver has a reaction time of Td (1.0 s late, 1.5 s early) and decelerates at α f (7.35 m/s2).
Procedure When participants arrived at the simulation facility, they were given an information summary and informed consent form and were briefed on operation of the simulator vehicle. To reduce anticipation of rearend crashes, they were told that they would participate in a study to assess the fidelity of the simulator. They were instructed to pay particular attention to the feel of the steering, accelerator pedal, brakes, interaction with the other vehicle controls, and the realism of the traffic. Participants were then escorted to the simulator dome and briefed by the ride-along observer about how to assess the fidelity of the simulator. Participants then drove a 5-min practice drive. Participants in the collision warning condition were introduced to the collision warning system before driving and performed two “looming” maneuvers on a practice lead vehicle so they could see how it functioned. These participants were asked whether they felt that the collision warnings came on too soon or too late for each of the two looming events. Subjects in the baseline condition were asked to drive as close to the practice lead vehicle as was comfortable, and then to back off. Each subject performed this maneuver twice. Following the practice drive, participants continued driving on the rural two-lane highway until they came to a freeway entrance and merged onto a multilane freeway. After about 5 mi, subjects came to an on-ramp, where a vehicle merged in front of the participant’s vehicle. This scenario forced the subject driver to react to another scenario vehicle and activated the collision warning display. After this interaction, the driver continued on the multilane freeway. Several miles later, the participant encountered another lead vehicle (a truck in this case). The simulator scenario then “coupled” the subject vehicle with the truck at a 3.2-s headway. Once the vehicles were coupled, a digitized voice came over the vehicle’s speakers and asked the driver to “press the button above the rear-view mirror until the red light comes on.” Since it was important that all participants be distracted (e.g., looking away from the forward roadway) during the critical event, drivers who did not look away from the forward roadway were removed from the data analysis. Three drivers ultimately did not fit this a priori criterion and were replaced. Three hundred ms after the driver pressed the button above the rearview mirror, the truck swerved to the center lane and exposed a stopped passenger vehicle in the right lane. Corresponding to the
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swerve of the truck, the collision warning display was triggered using one of the two warning times, which cycled quickly to the auditory horn warning. A shadowing vehicle was also positioned to the left of the subject so that an easy lane change was not possible. Drivers had to avoid the shadowing vehicle if they attempted to change lanes. The baseline condition provided no information to drivers on safe or unsafe headway or dangerous relative velocities regarding the lead vehicle in a stationary lead vehicle scenario. Subjects had to depend on their own judgment in reacting to lead vehicles throughout the drive.
Dependent Measures The statistical analysis concentrated on driver reaction to the final event. The following data were collected for each subject in both the baseline and warning display experimental conditions.
Impact with the Lead Vehicle An impact was defined as any instance when a participant’s vehicle struck any portion of the lead vehicle.
Speed on Impact If the participant vehicle collided with the stationary vehicle, the impact speed was recorded to assess the severity of each crash.
Time-to-Collision Time-to-collision (TTC) was measured at the following: 1. Initial accelerator release, defined as the exact point at which the driver began to release the accelerator pedal as a result of reacting to the uncovering of the stationary vehicle. The upward motion of the foot must have been continuous such that the next move was completely off of the accelerator pedal. 2. Final accelerator release, defined as the point at which the driver had less than 10% force on the accelerator pedal as a result of releasing it. This point was chosen in addition to the initial accelerator release because it was more defined, whereas initial accelerator release was subject to some interpretation and varied depending on how fast the driver was releasing the accelerator pedal. 3. Initial braking, defined as the point at which the subject’s foot was over the brake pedal and moving downward to initiate braking. 4. Brake application, defined as the point at which the driver had put at least 10% braking force on the brake pedal. This point was chosen in addition to the initial braking point because it was more easily defined. 5. Initial steering, defined as the participant initiating a steering input of at least 6° at a rate of at least 15°/s. 6. Maximum steering, defined as the maximum steering input recorded during the reaction sequence.
Transition Time Between Accelerator Release and Brake Input Two times exist, the initial accelerator release to initial braking input and the final accelerator release to braking input. Accelerator-to-full-
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brake transition time was defined as the time between when the foot began to release the accelerator and when it began to touch the brake.
Transportation Research Record 1803
Normal Driving
Mean Response Time Initial driver action was defined as the first action the subject performed after the incurring vehicle initiated movement. Subjects could either begin to release the accelerator pedal or begin to steer as part of this measure. This allowed greater accuracy in the measurement of when the subject recognized the threat and performed an initial crash avoidance action.
Identify Hazard
Decide Action
Maximum Brake Pressure Input Brake pressure is a measure of brake line fluid pressure. Maximum brake pressure provides a good estimate of the force a subject has exerted on the brake pedal.
Maximum Steering Input Maximum steering input was measured using the greatest steering wheel deviation to either the left or the right. Steering wheel deviation was measured in degrees, with zero being the midpoint and 480° being the maximum magnitude of steering wheel deviation in either direction.
Maximum Lateral Acceleration Maximum lateral acceleration is a measure of the severity of a steering maneuver. The simulator dynamics model used for this experiment allowed minimal lateral control by steering when the brakes were “locked.” This feature was incorporated to simulate the behavior of an actual vehicle with locked brakes. Because the maximum value of lateral acceleration correlated highly with steering manipulation, the analysis of maximum lateral acceleration would result in a pattern similar to that of steering input (i.e., maximum steering input). Evaluation of Driver Response Assessing driver response can be a difficult task. The analyst must go through the video frame by frame and examine the entire reaction numerous times to ensure that all stages of the driver’s perceptionreaction/action sequence are understood. The driver reaction sequence is a complex interaction that generally begins when drivers identify a hazard. They must then predict the action of the threatening vehicle, decide on an action, and finally, execute a maneuver (steering or braking, or both). Secondarily, drivers may adjust their maneuvers on the basis of their perception of how the threat changes—either identifying a subsequent threat or adjusting their decisions and actions on the basis of changes in the threatening car’s behavior. A brief model is shown in Figure 2 that describes the driver reaction sequence the data analyst must examine.
Execute Maneuver
Resume Normal Driving
FIGURE 2 Model of driver reaction sequence.
formed to determine whether the driver warning system provided a benefit over the baseline in terms of initial accelerator pedal release, accelerator to brake pedal transition time, brake application time, crash frequency, and overall reaction time. Success or lack of success in avoiding the crash was also examined for each condition.
RESULTS AND DISCUSSION In reporting results, an alpha significance level of .05 will be applied to all analyses of variance and simple effect analyses using the Tukey test (17 ) for post hoc comparisons. This sets a 95% confidence that the hypothesis is correct for the particular test. Actual significance levels are shown in parentheses. There were three primary significant variables in the experiment: mean overall driver response latency, TTC at initial accelerator release, and number of crashes by warning time.
Mean Driver Response Time When the initial driver response time was examined (Figure 3), a significant effect was found for the early warning condition ( p = .0452) where drivers responded faster than the baseline group. Initial driver response was defined as the first action the driver took in response to the stopped vehicle (in the form of braking or steering). Drivers in the early warning condition responded in 1.93 s, in 2.23 s in the late warning condition, and in 2.53 s in the baseline. These results suggest that drivers were able to respond more quickly with the early warning display relative to the baseline.
Data Analysis
TTC at Accelerator Release
The overall reaction sequence was decomposed for the last event. Inferential statistics analysis (e.g., analysis of variance) was per-
Initial accelerator release is generally the first stage of the reaction sequence and is indicative of the overall urgency of the driver’s
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3.5
3 2.53 1.93
2 1.5 1 0.5
2.5
1.5 1 0.5 0
Baseline
Early Warning
FIGURE 5
Mean driver reaction time.
TTC at Final Accelerator Release The results indicated that the final accelerator release point (the neutral position of the accelerator pedal) is also significant (p = .0114). The TTC values were 2.88 s for the early warning condition, 2.52 s for the late warning condition, and 2.38 s for the baseline condition. The significant difference between early warning condition and the baseline condition indicates that participants were able to release the accelerator pedal with a greater safety margin in the early warning condition than in the baseline condition (see Figure 5). Speed and Number of Impacts with the Stationary Vehicle Examination of the number of impacts with the stationary vehicle indicates that one crash occurred in the early warning condition, five
3.5
Late Warning
TTC at final accelerator release.
6
3.18 2.72
2.56
Early Warning
crashes for the late warning, and three crashes for the baseline (Figure 6). While the increase of crashes in the late warning condition relative to the baseline is disconcerting, functionally, the speed at impact becomes a more important safety benefit to examine. The early warning clearly showed a benefit in terms of both number of impacts and speed at impact. Of the three impacts that occurred in the baseline condition, the mean speed at impact was 61 km/h (37.9 mph), whereas the mean speed in the one impact that occurred in the early warning time condition was 30.6 km/h (19 mph) (Figure 7). As shown in Figure 8, drivers used three maneuvers to avoid the stationary lead vehicle: steering to the right while braking, steering to the left while braking, and braking only. Although the scenario included a blocking vehicle in the lane to the left of the subject vehicle, eight drivers were able to brake and steer to the left without hitting the blocking vehicle. There was no vehicle or object that prevented the driver from steering to the right to avoid the stationary lead vehicle. All participants released the accelerator and then applied the brakes as primary avoidance maneuvers. Seventeen of the 30 subjects used right (9) or left (8) steering maneuvers as secondary avoidance maneuvers. For the late warning condition, four of the five collisions occurred when the drivers braked only. In all, seven of the nine collisions occurred with drivers that only applied the brakes. This last finding is quite interesting; it may be that the late warning interferes with drivers’ processing of information as the collision situation evolves. Although the initial response is faster with the late warning, the proportion of crashes in which drivers only braked suggests that the processing of the warning might have interfered with the perception and decision process associated with modulating the response. Drivers with the late warning failed to augment
2.5 2 1.5 1 0.5
5 Lead Vehicle Impacts
TTC (seconds)
Baseline
Late Warning
reaction. The warning had a significant effect on participants’ response to the collision situation. Participants released the accelerator significantly sooner in the early warning condition than those in the baseline condition, resulting in a 24% increase in TTC at initial accelerator release (Figure 4). The TTC values were 3.18 s for the early warning condition, 2.72 s for the late warning condition, and 2.56 s for the baseline (p = .0141). The early warning condition provided drivers a greater safety margin relative to the late warning and baseline. Interestingly, the late warning accelerator release TTC was only slightly greater than the baseline (no display).
5 4 3 3 2 1 1 0
0 Baseline FIGURE 4
2.52
2.38
2
0
3
2.88
3
2.23 TTC (seconds)
Time (seconds)
2.5
FIGURE 3
5
Early Warning
TTC at initial accelerator release.
Baseline
Late Warning FIGURE 6
Early Warning
Number of impacts of the lead vehicle.
Late Warning
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37.9
35 Speed (mph)
30 23.1
25 19
20 15 10 5 0 Baseline
FIGURE 7
Early Warning
Late Warning
Mean speed at impact.
their braking response with a steering response. This is consistent with the greater number of collisions but lower mean collision velocity. These results also suggest that voice warnings that command certain responses (e.g., “brake”) might lead drivers to neglect other effective responses, such as steering (18). Thus, a late warning issued as a command might undermine driver safety.
CONCLUSIONS The primary objective of this study was to investigate whether drivers operating vehicles equipped with a front-to-rear-end collision warning system in a stationary lead vehicle scenario would exhibit enhanced front-to-rear-end collision avoidance behavior relative to those driving without such a system. A secondary objective was to explore whether the timing of the warning affected driver reaction and performance. The results indicate that an in-vehicle collision warning system with an early alert can provide drivers with information to help them avoid a rear-end collision, shorten response times, and slow impact speeds relative to those who do not have similarly equipped vehicles. Other interesting results suggest that a late warning time may distract drivers at the last moment. This may have been a contributing factor in the significant increase in collisions for the late warning condition. Another simulator study examining the effects of warnings issued during a driver response suggests that warnings that occur while
7 Brake & Steer Left 6
Brake Only Brake & Steer Right
5 4 3 2 1 0 Baseline FIGURE 8
Early Warning
Driver avoidance maneuver.
Late Warning
a driver is in the midst of a maneuver, during the first 250 ms, actually work to hasten subsequent responses (19). On the basis of these findings, it seems that when a warning is received early it acts to speed the driver’s response. However, if the alert is presented to the driver during response planning, it may interfere with response execution. Brown et al. (19) also found that if a warning is received just after a response has been initiated, it acts to speed the subsequent response. Although not statistically significant, the functional differences in potential injuries and fatalities between impact speeds of 30.6 km/h (19 mph) (early warning time) versus 61.2 km/h (38 mph) (baseline) are large. On the basis of the assumption that crash severity is proportional to kinetic energy, the warning provides a 75% reduction in collision severity. Relating this reduction in collision severity to the driver reaction time component in an algorithm is important in the design of FCW systems. The results indicate a 500-ms decrease in driver response for the early warning. As Seiler et al. (16) point out, a 500-ms decrease in response time could reduce rear-end crashes by 62%—similar to the findings in this study. Previous IDS experiments that examined driver reaction to a highdeceleration event (20) found differences in late and early warning conditions during crash circumstances. In that study, drivers who were warned at too great a distance (3.2 s) from the decelerating vehicle showed no benefit over the baseline condition; drivers warned closer (2.7 s) to the decelerating vehicle showed a significant benefit in driver reaction and crash mitigation. The results of this experiment also suggested that drivers must be close enough to perceive the lead vehicle as a threat as the warning is being issued.
ACKNOWLEDGMENTS The authors wish to thank the National Highway Traffic Safety Administration (NHTSA) for funding this research. Special thanks go to Arthur Carter, the NHTSA technical leader of this project.
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10. Burgett, A., A. Carter, R. Miller, W. Najm, and D. Smith. A Collision Warning Algorithm for Rear-End Collisions. NHTSA, 1998. 11. Dingus, T. A., D. V. McGehee, R. N. Manakkal, S. J. Jahns, J. M. Hankey, and C. Carney. Human Factors Field Evaluations of Automotive Headway Maintenance/Collision Warning Devices. Human Factors, Vol. 39, No. 2, 1997, pp. 216–229. 12. Lee, J., D. V. McGehee, T. A. Dingus, and T. Wilson. Collision Avoidance Behavior of Unalerted Drivers Using a Front-to-Rear-End Collision Warning Display on the Iowa Driving Simulator. In Transportation Research Record 1573, TRB, National Research Council, Washington, D.C., 1997, pp. 1–7. 13. McGehee, D. V., T. Brown, and T. Wilson. Examination of Drivers’ Collision Avoidance Behavior in a Stationary Lead Vehicle Situation Using a Front-to-Rear-End Collision Warning System. Contract DTNH2293-C-07326. NHTSA Office of Crash Avoidance Research Technical Report, 1998. 14. McGehee, D. V., T. A. Dingus, and A. D. Horowitz. An Experimental Field Test of Automotive Headway Maintenance/Collision Warning Visual Displays. Proceedings of the Human Factors and Ergonomics Society, 1994, pp. 1099–1103.
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15. Suetomi, T., and K. Kido. Driver Behavior Under a Collision Warning System—A Driving Simulator Study. SAE Technical Publication, 970279, 1997. 16. Seiler, P., B. Song, and J. Hedrick. Development of a Collision Avoidance System. SAE Technical Publication, 980853, 1998. 17. Walpole, R. E., and R. H. Myers. Probability and Statistics for Engineers and Scientists, 6th ed. Prentice Hall, N.J., 1997. 18. Lee, J. D., B. F. Gore, and J. L. Campbell. Display Alternatives for InVehicle Warning and Sign Information: Message Style, Location, and Modality. Transportation Human Factors Journal, Vol. 1, No. 4, 1999, pp. 347–377. 19. Brown, T. L., J. D. Lee, and J. Hoffman. The Effect of Rear-End Collision Warnings on On-Going Response. Presented at 45th Annual Meeting of the Human Factors and Ergonomics Society, Minneapolis, Minn., 2001. 20. McGehee, D. V., J. Lee, and T. A. Dingus. Collision Avoidance Behavior of Unalerted Drivers Using a Front-to-Rear-End Collision Warning Display on the Iowa Driving Simulator. Contract No. DTNH22-93-C07326. Frontier Engineering, NHTSA Technical Report, 1996. Publication of this paper sponsored by Committee on Vehicle User Characteristics.
