University of Michigan, Ann Arbor, Industry Affiliation Program for Human Factors in Transportation Safety

The IVBSS program is a four-year, two-phase project to design and evaluate an integrated crash warning system for forward collision, lateral drift, lane-change merge, and curve speed warnings for both light vehicles and heavy trucks. This report, covering human factors research and DVI development in the first two years of the program, describes five laboratory studies, four driving simulator studies, and two onroad pilot tests conducted to assess a variety of river-interface concepts related to the development of integrated warning systems. Selected major findings are as follows: 1) For the vehicles selected, warning sounds should be at least 80 dB(A) in the 1 to 5 KHz range. 2) Auditory warning durations should be less than the expected mean response time. 3) No approaches to warning combination (single, dual-simple, dual-hybrid, or multiple warnings) led to noticeably better driver responses, though drivers favored the multiple warning approach least, and for a variety of reasons a dual-warning approach is recommended for IVBSS. 4) Delays between 150 and 300 ms are acceptable for the LDW algorithm. 5) No single prioritization scheme for warnings (simultaneous, priority interrupt, or delayed presentation) is recommended based on the findings from a simulator study. Extended pilot testing is likely to suggest minor refinements to the DVIs developed here. In the pilot tests that have been conducted, all of the warning systems operated as planned, with some changes required to reduce false alarm rates. Overall, drivers reported IVBSS to be intuitive and easy to use. Most drivers stated warnings were received with about the right frequency, and in general the warnings were not distracting. Results from the laboratory and simulator experiments, in particular, are likely to assist future developers of driver-vehicle interfaces for integrated crash warning systems.

Data from 36 drivers involved in a naturalistic driving study was analyzed to determine the frequency and conditions under which drivers engage in secondary behaviors and to explore the relationship these behaviors might have with driving performance. Researchers coded 1,440 five-second video clips of the drivers’ faces for the occurrence of specific secondary behaviors and the duration of glances away from the forward scene. Corresponding performance data from the instrumented vehicles were used to calculate variability of steering angle, mean and variability of lane position, mean and variability of throttle position, and variability of speed. All categories of secondary behavior were associated with significantly higher variability in steering angle. The results for other performance measures were mixed. In summary; driving performance measures vary with differing tasks, with no single driving performance indicator that is obviously predictive of drivers’ engagement in secondary tasks.

The Road Departure Crash Warning System Field Operational Test (RDCW FOT) was conducted to assess the safety impacts, driver acceptance levels, and the maturity of road departure crash warning systems as installed on a light vehicle platform. This paper presents the experimental design, performance of the road departure system in naturalistic use, and analyses of safety impacts of the technology using surrogate measures. Use of the system led to a 50% reduction in the observed rate of events in which the equipped vehicle came within 0.1 m of a lane edge in steady-state lane-keeping situations. Lane changes performed without the use of a turn signal were reduced by 43% on freeways and ramps and 24% on surface roads. Levels of lateral acceleration in curves was not significantly different, except on ramps, where a significant change in the 90th percentile values of lateral acceleration were observed for a within-subject comparison. There were no observed effects of risk homeostasis and no evidence of significant negative unintended consequences.

This report summarizes results from the Intelligent Vehicle Initiative (IVI) Road Departure Crash Warning System Field Operational Test (RDCW FOT) project. This project was conducted under a cooperative agreement between the U.S. Department of Transportation and the University of Michigan Transportation Research Institute, along with its partners, Visteon Corporation and AssistWare Technologies. Road departure crashes account for 15,000 fatalities annually in the U.S. This project developed, validated, and field-tested a set of technologies intended to warn drivers in real time when the driver was drifting from their lane, and a curve-speed warning system designed to provide alerts to help drivers slow down when approaching a curve too fast to safely negotiate the curve. This report describes the field operational test of the system and subsequent analysis of the data to address the suitability of similar systems for widespread deployment within the U.S. passenger-vehicle fleet. Two areas were addressed: safety-related changes in driver performance including behavior that may be attributed to the system, and levels of driver acceptance in key areas. Testing used 11 passenger sedans equipped with RDCW and a data acquisition system that compiled a massive set of numerical, video, and audio data. Seventy-eight drivers each drove a test vehicle, unsupervised, for four weeks. The resulting data set captured 83,000 miles of driving, with over 400 signals captured at 10 Hz or faster. Analysis of the data shows that with the RDCW system active, relative to the baseline condition, drivers improved lanekeeping by remaining closer to the lane center and reducing the number of excursions near or beyond the lane edges. In addition, turn signal use increased dramatically. The data, however, were unable to confirm a change in driver’s curve-taking behaviors that could have been attributed to the curve speed warning system. Driver acceptance was generally positive in relation to the lateral drift component of the system, with reactions to the curve speed warning system being rather mixed. Many additional results and insights are documented in the report.

Infrared-reflective (IRR) treatment of automotive glass has been shown to reduce air temperature in vehicle cabins, thereby increasing fuel economy and occupant comfort. Its effect on radiant heat, however, may augment these benefits. In this study, the hypothesis that radiant heat affects subjective comfort ratings in a vehicle was tested. IRR films were systematically applied to the driver-side window of an outdoor stationary vehicle. In Phase 1, cabin air temperature was controlled while participants rated their thermal comfort. In Phase 2, air temperature was adjusted according to participants' responses. Results in Phase 1 showed that the IRR treatment improved thermal comfort on the left forearm, which was exposed to direct solar irradiance, but not whole-body thermal comfort. In Phase 2, participants indicated that they were comfortable at a higher air temperature (mean of 2.5°F [1.4°C]) with the IRR treatment than in the untreated condition. The results indicate that reducing radiant heat via IRR treatment affects subjective assessments of thermal comfort and allows occupants to maintain the same level of comfort in a warmer vehicle cabin. Applications of this research include future implementations of IRR treatment on automotive glass that may lead to greater fuel economy savings and occupant comfort than have previously been estimated.

Lateral Drift Warning (LDW) and Curve Speed Warning (CSW)systems were developed to address two main critical events in run-off-roadcrashes, which are road edge departure and excessive speed. The LDW systemused a two-stage alert system, with the first stage activating when the driverdeparted a lane with a dashed boundary and the imminent, or second stage, whendeparting a lane with a solid boundary. The CSW also employed a two-stage alert,with the level based on the degree of over-speed for the upcoming curve. Thehaptic modality, in the form of seat vibration, was chosen as the first levelwarning for both systems, and auditory was chosen as the second or most urgentlevel. The two systems were installed in a fleet of instrumented vehicles andloaned to 78 randomly selected licensed drivers for approximately 4 weeks.Debriefing questions detailing the driver’s experience with the system wereadministered and analyzed in a two by two design of modality by system. Afterexamination of both the statistical results and the open-ended comments, thequestion of which modality is most appropriate is still uncertain. Each modalityhad positive aspects. Haptic does not alert the entire car and participants alsoconsidered it less distracting. Auditory provided better recognition betweenwarnings and participants were better able to understand the meaning and therequired response for each warning.

The authors tested the hypothesis that reducing radiant heat by the application of an infrared-reflective (IRR) treatment will allow occupants to maintain the same level of comfort in a warmer vehicle cabin. Participants were passengers in a mid-sized sedan that was driven for 46 minutes along a 41.5-mile route. Each participant experienced two drives: one with IRR film applied to all glazing surfaces of the vehicle, and one with no IRR treatment applied. Every two minutes, participants were asked to rate their thermal sensation at five body locations and to indicate whether, overall, they felt too hot or too cold. Cabin air temperature in the vehicle was raised or lowered depending on participants' responses. Although the IRR treatment did not have a statistically significant effect on the air temperature that participants found comfortable, the trend was in the expected direction, and a decrease in the average time required to reach thermal comfort was observed. IRR-treated drives were also associated with reductions in air conditioner compressor use and fuel consumption. While the physical effects in this study confirmed findings of previous studies, data concerning the relationship between radiant heat and comfortable air temperature were more complicated and inconclusive and would benefit from further research.

Performed for the University of Michigan Industry Affiliation Program for Human Factors in Transportation Safety

A green windshield at night reduces acuity from 20/32 to 20/46, and combined with pink glasses to 20/60. Resolution thresholds decreased from 10 to 42 seconds of arc, so that a pair of objects that could be seen through a clear windshield at 100 feet decreased to 25 feet through the green. Other visual functions found "defective in night-driving conditions with tinted glass" were stereo acuity, instant counting span, discrimination of angular velocity, simultaneous contrast, intensity change, and direction of a line target." Headlights should be designed larger in area "since glare is inversely proportional to the area of the source." Title: Effect of aftermarket automobile window tinting films on driver vision (LaMotte et al., 2000). Abstract: This study was conducted to determine the level of automobile window tint that causes a significant reduction of vision for automobile drivers. Contrast sensitivity was measured on 20 participants, of whom 10 were age 20 to 29 years and 10 were age 60 to 69 years, through a stock automobile window (control) and two windows darkened with plastic film. For the younger drivers, a car window with 37% transmittance did not significantly reduce contrast sensitivity, but a darker tint of 18% transmittance reduced contrast sensitivity at higher spatial frequencies. For the older drivers, a tint of 37% transmittance significantly reduced midtohigh spatial frequency contrast sensitivity. The typical state standard (no tint with less than 35% transmittance) would thus seem to be appropriate for younger drivers; however, further examination of the standard may be necessary in regard to older drivers. Actual or potential applications of this research include guidelines and regulations regarding tinting of automobile windows. This study was conducted to determine the level of automobile window tint that causes a significant reduction of vision for automobile drivers. Contrast sensitivity was measured on 20 participants, of whom 10 were age 20 to 29 years and 10 were age 60 to 69 years, through a stock automobile window (control) and two windows darkened with plastic film. For the younger drivers, a car window with 37% transmittance did not significantly reduce contrast sensitivity, but a darker tint of 18% transmittance reduced contrast sensitivity at higher spatial frequencies. For the older drivers, a tint of 37% transmittance significantly reduced midtohigh spatial frequency contrast sensitivity. The typical state standard (no tint with less than 35% transmittance) would thus seem to be appropriate for younger drivers; however, further examination of the standard may be necessary in regard to older drivers. Actual or potential applications of this research include guidelines and regulations regarding tinting of automobile windows.