Daniel V. McGehee

Collision Warning Timing, Driver Distraction, and Driver Response to Imminent Rear-End Collisions in a High-Fidelity Driving Simulator:

Rear-end collisions account for almost 30% of automotive crashes. Rear-end collision avoidance systems (RECASs) may offer a promising approach to help drivers avoid these crashes. Two experiments performed using a high-fidelity motion-based driving simulator examined driver responses to evaluate the efficacy of a RECAS. The first experiment showed that early warnings helped distracted drivers react more quickly---and thereby avoid more collisions---than did late warnings or no warnings. Compared with the no-warning condition, an early RECAS warning reduced the number of collisions by 80.7%. Assuming collision severity is proportional to kinetic energy, the early warning reduced collision severity by 96.5%. In contrast, the late warning reduced collisions by 50.0 % and the corresponding severity by 87.5%. The second experiment showed that RECAS benefits even undistracted drivers. Analysis of the braking process showed that warnings provide a potential safety benefit by reducing the time required for drivers to release the accelerator. Warnings do not, however, speed application of the brake, increase maximum deceleration, or affect mean deceleration. These results provide the basis for a computational model of driver performance that was used to extrapolate the findings and identify the most promising parameter settings. Potential applications of these results include methods for evaluating collision warning systems, algorithm design guidance, and driver performance model input.

Simulated Car Crashes at Intersections in Drivers With Alzheimer Disease

Current evidence suggests that car crashes in cognitively impaired older drivers often occur because of failure to notice other drivers at intersections. We tested whether licensed drivers with mild to moderate cognitive impairment due to Alzheimer disease (AD) are at greater risk for intersection crashes. In this experiment, 30 participants drove on a virtual highway in a simulator scenario where the approach to within 3.6 seconds of an intersection triggered an illegal incursion by another vehicle. To avoid collision with the incurring vehicle, the driver had to perceive, attend to, and interpret the roadway situation; formulate an evasive plan; and then exert appropriate action on the accelerator, brake, or steering controls, all under pressure of time. The results showed that 6 of 18 drivers with AD (33%) experienced crashes versus none of 12 nondemented drivers of similar age. Use of a visual tool that plots control over steering wheel position, brake and accelerator pedals, vehicle speed, and vehicle position during the 5 seconds preceding a crash event showed inattention and control responses that were either inappropriate or too slow. The findings were combined with those in another recent study of collision avoidance in drivers with AD that focused on potential rear end collisions. Predictors of crashes in the combined studies included visuospatial impairment, disordered attention, reduced processing of visual motion cues, and overall cognitive decline. The results help to specify the linkage between decline in certain cognitive domains and increased crash risk in AD and also support the use of high-fidelity simulation and neuropsychologic assessment in an effort to standardize the assessment of fitness to drive in persons with medical impairments.

Human factors field evaluation of automotive headway maintenance/collision warning devices

Three on-road studies were conducted to determine how headway maintenance and collision warning displays influence driver behavior. Visual perspective, visual perspective with a pointer, visual perspective combined with an auditory warning, discrete visual warning, and discrete auditory warning were assessed during both coupled headway and deceleration events. Results indicate that when drivers are provided with salient visual information regarding safe headways, they utilize the information and increase their headway when appropriate. Auditory warnings were less effective than visual warnings for increasing headways but may be helpful for improving reaction time during events that require deceleration. Drivers were some what insensitive to false alarm rates, at least during short-term use. Finally, and most important, driver headway maintenance increased by as much as 0.5 s when the appropriate visual display was used. However, a study to investigate the long term effects of such displays on behavior is strongly recommended prior to mass marketing of headway maintenance/collision warning devices.

Effects of Age, System Experience, and Navigation Technique on Driving with an Advanced Traveler Information System

This paper explores the effects of age, system experience, and navigation technique on driving, navigation performance, and safety for drivers who used TravTek, an Advanced Traveler Information System. The first two studies investigated various route guidance configurations on the road in a specially equipped instrumented vehicle with an experimenter present. The third was a naturalistic quasi-experimental field study that collected data unobtrusively from more than 1200 TravTek rental car drivers with no in-vehicle experimenter. The results suggest that with increased experience, drivers become familiar with the system and develop strategies for substantially more efficient and safer use. The results also showed that drivers over age 65 had difficulty driving and navigating concurrently. They compensated by driving slowly and more cautiously. Despite this increased caution, older drivers made more safety-related errors than did younger drivers. The results also showed that older drivers benefited substantially from a well-designed ATIS driver interface.

Human performance models and rear-end collision avoidance algorithms

Collision warning systems offer a promising approach to mitigate rear-end collisions, but substantial uncertainty exists regarding the joint performance of the driver and the collision warning algorithms. A simple deterministic model of driver performance was used to examine kinematics-based and perceptual-based rear-end collision avoidance algorithms over a range of collision situations, algorithm parameters, and assumptions regarding driver performance. The results show that the assumptions concerning driver reaction times have important consequences for algorithm performance, with underestimates dramatically undermining the safety benefit of the warning. Additionally, under some circumstances, when drivers rely on the warning algorithms, larger headways can result in more severe collisions. This reflects the nonlinear interaction among the collision situation, the algorithm, and driver response that should not be attributed to the complexities of driver behavior but to the kinematics of the situation. Comparisons made with experimental data demonstrate that a simple human performance model can capture important elements of system performance and complement expensive human-in-the-loop experiments. Actual or potential applications of this research include selection of an appropriate algorithm, more accurate specification of algorithm parameters, and guidance for future experiments.

DRIVER REACTION TIME IN CRASH AVOIDANCE RESEARCH : VALIDATION OF A DRIVING SIMULATOR STUDY ON A TEST TRACK

A series of experiments was conducted on the Iowa Driving Simulator to examine driver reaction and performance in an intersection incursion crash scenario. To validate these simulator trials, a second study was run on a test track using a similar intersection incursion scenario to examine driver reaction and vehicle performance. Results showed that there was statistical equivalence between important driver reaction times with both studies.

Effects of Adaptive Cruise Control and Alert Modality on Driver Performance

This article reports on a study that assessed the ability of automobile drivers to make the transition from adaptive cruise control (ACC) to manual control when warned with alerts of different modalities. The authors compared how drivers maintain headway distance in conditions with and without ACC in mild, moderate, and severe braking situations. The different modalities tested include visual, auditory, seat vibration, brake pulse, and a combination of these methods. The two scenarios studied were a braking lead vehicle and an abrupt lane change of a lead vehicle that reveals a slow-moving vehicle. The study included sixty people aged 30 to 50 years, split evenly by gender and used to using cruise control (defined as at least twice per month). After a demographic questionnaire and pre-drive instruction, participants drove a 6-minute practice drive, followed by a 35-minute experimental drive. The results showed that ACC helped drivers maintain a larger safety margin, as measured by the minimum time-to-collision (TTC). The authors hypothesize that this larger safety margin may have important indirect benefits, affecting other drivers and the overall traffic flow rather than the likelihood of a crash for the driver using the ACC. The various alert modalities performed similarly when considered independently. There was a slightly greater minimum TTC associated with the brake pulse in moderately severe situations. Readers are referred to the full report at www.ntis.gov (access number PB2009-102474). Keywords: Driver distraction;

Effect of warning timing on collision avoidance behavior in a stationary lead vehicle scenario

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.

Comparison of Driver Braking Responses in a High-Fidelity Simulator and on a Test Track

The braking responses of drivers in the Iowa Driving Simulator (IDS) were compared with those of drivers on a test track. The braking profile of drivers was compared in last-minute braking situations in which drivers were instructed to brake “normally” or “hard.” Although the motion and visual cues in the IDS are imperfect, the data agree in many respects. The general pattern of results is similar, with the initial speed and lead vehicle deceleration affecting drivers on the test track and in the simulator in a similar way. In several experimental conditions, the similarity of the responses went beyond the general pattern of response. The mean values were almost identical in several instances, and the values were frequently well within the confidence intervals. Although the simulator and test track drivers performed similarly, differences are apparent from the onset of braking, through the braking process, and in the outcome of the braking event. The instructions concerning normal and hard braking had little influence on the behavior of drivers in the simulator. Contributors to these differences include the limited visual and vestibular cues in the simulator and the extended practice on the test track.

FORWARD-LOOKING COLLISION WARNING SYSTEM PERFORMANCE GUIDELINES

This paper presents preliminary guidelines for a forward looking collision warning system. It addresses aspects of performance including general system requirements, driver/vehicle interface methodology, collision dynamics, standardized testing and estimation of associated benefits.