Heavy trucks, conspicuity treatment, and the decline of collision risk in darkness

In December 1992, Federal Motor Vehicle Safety Standard (FMVSS) 108, was amended to require conspicuity treatments on all heavy trailers manufactured after December 1, 1993. The standard was later modified and extended to tractors and older trailers such that by June 1, 2009 the entire fleet of tractors and semitrailers on United States roadways would reach full compliance with the regulation. To investigate the effect of the regulation, an analysis was conducted of the change in the odds that a fatal crash occurred in darkness, comparing scenarios in which the conspicuity treatment was likely to be influential to those in which the conspicuity treatment was likely to be irrelevant. From 1987 to 2009, the odds that a fatal collision involving a heavy truck occurred in darkness declined by 58% among the relevant crash scenarios, while little evidence of decline was found among the irrelevant scenarios. Disaggregations of crash scenario types suggest that the largest declines occurred in fatal rear end and angle collisions. A comparative analysis of light vehicles also found declines, although they were smaller and less sensitive to crash type. Similar but weaker trends were observed for nonfatal rear end collisions. The results are consistent with causal mechanisms that suggest that detection failure may be a significant contributor to the risk of striking a tractor-semitrailer in darkness, and that conspicuity treatments have significantly reduced this risk.The University of Michigan Industry Affiliation Program for Human Factors in Transportation Safetyhttp://deepblue.lib.umich.edu/bitstream/2027.42/89938/1/102820.pd

Factors affecting color correction of retroreflective markings

A nighttime field study was conducted to assess the effects of retroreflective material area, distribution, and color on judgments of conspicuity. Participants, seated in a stationary vehicle, took part in a pairwise comparison of the stimuli. The independent variables included retroreflective power, area and distribution of the retroreflective material, color of the retroreflective material, participant age, and participant gender. The results indicate that color (white, fluorescent yellow-green, and fluorescent red-orange) was a significant factor in the judgment of conspicuity, as might be predicted from the Helmholtz-Kohlrausch effect. In addition, color interacted with the distribution of material at the high level of retroreflective power. The area of the retroreflective material was also significant. The present study, in agreement with a number of previous studies, indicates that color influences the conspicuity of retroreflective stimuli, but that the results are not always in agreement with color correction factors prescribed in ASTM E 1501. The discrepancy between empirically derived color correction factors seems to be attributable to an interaction of the stimulus size (subtended angle) and color, which previous studies have not extensively examined. To a lesser degree, the retroreflective power of a material also appears to influence conspicuity. While the ASTM correction factors may be appropriate for intermediate subtended solid angles, particularly for nonsaturated colors, smaller correction factors appear appropriate for markings subtending small angles (approaching point sources), and larger factors for larger subtended angles of saturated stimuli.The University of Michigan Industry Affiliation Program for Human Factors in Transportation Safetyhttp://deepblue.lib.umich.edu/bitstream/2027.42/91263/1/102869.pd

LATCH usability in vehicles

This project investigated the usability of Lower Anchors and Tethers for CHildren (LATCH) hardware by measuring LATCH implementations in 98 2011 or 2010 model-year vehicles. ISO and SAE LATCH usability rating systems were used to assess all vehicles using data from the second row left position. Child restraint/vehicle interaction was assessed using both ISO and NHTSA proposed procedures. Volunteer testing was performed with 36 subjects on 12 different vehicles using 3 different child restraints, with each subject performing 8 child restraint installations. The results from the vehicle survey indicate that most vehicle manufacturers provide LATCH hardware at only the minimum number of locations required by FMVSS 225. Only 7 vehicles had three sets of LATCH hardware in the second row, while most of the remaining 91 vehicles were only equipped with LATCH in each outboard position and a tether anchor in the center position. In the 21 vehicles with a third row, four had no tether anchors and 11 had no lower anchors in the third row. The SAE child restraint fixture could not be installed in 27 vehicles, although head restraint interference was the cause of interference in only one vehicle. Fifty-nine vehicles met the SAE recommended lower attachment force of 75 N (16.9 lb) or less, while 15 vehicles required forces from 2 to 8 times this value. Only 2 vehicles met SAE recommendations for clearance angle of at least 75 degrees around the lower anchors. The depth of the lower anchors relative to the bight is less than 2 cm in 28 vehicles, 2-4 cm in 34 vehicles, and greater than 4 cm in 36 vehicles. The most common location for the tether anchor is the seatback (42) and package shelf (35). The lower anchors are marked in 77 vehicles, while the tether anchors are marked in 68 vehicles. Only Ford products clearly specify weight ranges for use of LATCH hardware in their manuals. Many vehicle manuals are not clear on how the head restraint should be positioned during child restraint installation. ISO ratings of vehicle LATCH usability ranged from 41% to 78%, while vehicles assessed using the SAE draft recommended practice met between 2 and all 10 of the recommendations. There was a slight correlation between vehicles meeting SAE recommended practices and ISO usability ratings. Twenty vehicles with a range of vehicle features were assessed using the ISO vehicle/child restraint form and 7 child restraints; ISO vehicle/child restraint interaction scores ranged from 14% to 86%. Based on these interaction scores, the Cosco Alpha Omega, the Chicco KeyFit, and Evenflo Maestro were used with a subset of 12 vehicles to perform volunteer testing and assess the quality of subject installations. No vehicle factors predicted tether use or correct use of tether. However, the correct use of lower anchors was associated with a lower anchor clearance angle greater than 54°, an attachment force of 40 lb or less, and lower anchor depth within the bight of less than 2 cm. Correct lower anchor use also had 3.3 times higher odds of tight installation compared to incorrect use.Insurance Institute for Highway Safetyhttp://deepblue.lib.umich.edu/bitstream/2027.42/90856/1/102854.pd

Driver distraction from cell phone use and potential for self-limiting behavior

This project consists of three parts. The first is a review of the literature on driver distraction that primarily focuses on cell phone use. The second two parts involve analysis of an existing field operational test (FOT) database to examine: 1) self-limiting behavior on the part of drivers who use cell phones, and 2) eye glance patterns for drivers involved in cell phone conversations and visual-manual tasks (e.g., texting) as compared to no-task baseline driving. The literature review discusses the apparent contradiction between results of case-crossover and simulator studies that show increases in instantaneous risk due to talking on a cell phone and results of crash-data analyses that show no substantial increase in crashes associated with increases in cell phone use in vehicles. The first data analysis shows some evidence of self-limiting behavior in cell phone conversations. Drivers initiate calls when on slower roads and at slower speeds, often when stopped. However, they call more at night, which is a higher-risk time to drive. The second analysis showed that eye glances when talking on the phone are fixated on the road for longer periods of time than in baseline driving. In contrast, on-road eye glances when engaged in a visual-manual (VM) task are short and numerous. Eye glances on and off the road are about equal in length, and the average total off-road gaze time for a five-second interval is about 2.8 secs, or 57% of the time. Average off-road gaze time out of five seconds in baseline driving is about 0.8 sec, or 16% of the time. Results show the differences in distraction mechanism between cell-phone conversations and texting. Ramifications for potential interventions are discussed.State Farm Insurancehttp://deepblue.lib.umich.edu/bitstream/2027.42/108381/1/103022.pd

The Evolution of Distorted Rotating Black Holes III: Initial Data

In this paper we study a new family of black hole initial data sets corresponding to distorted ``Kerr'' black holes with moderate rotation parameters, and distorted Schwarzschild black holes with even- and odd-parity radiation. These data sets build on the earlier rotating black holes of Bowen and York and the distorted Brill wave plus black hole data sets. We describe the construction of this large family of rotating black holes. We present a systematic study of important properties of these data sets, such as the size and shape of their apparent horizons, and the maximum amount of radiation that can leave the system during evolution. These data sets should be a very useful starting point for studying the evolution of highly dynamical black holes and can easily be extended to 3D.Comment: 16 page

Improving the repeatability and reproducibility of belt fit measurement with 6YO and 10YO ATDs

In previous work, researchers at the University of Michigan Transportation Research Institute (UMTRI) developed a method for quantifying the belt fit provided by belt-positioning boosters by measuring the belt location relative to the six- and ten-year-old Hybrid-III dummies. In another study, the torso and lap belt scores obtained by this method were found to be closely related to the belt fit obtained by similar-size children across a wide range of booster and belt conditions. The Insurance Institute for Highway Safety (IIHS) adapted the UMTRI procedure to develop a rating system for booster belt fit, but adoption by other labs has been slowed by difficulty in obtaining repeatable results. The current study was undertaken to improve the repeatability and reproducibility across operators of the procedure. The modifications made by IIHS were studied and most incorporated, and a number of other issues were examined through pilot testing. A revised version of the procedure was tested with repeated measurements by three operators in six boosters. The results were analyzed to quantify the variance associated with the operators, the installation of the booster and dummy, and the routing of the belt. The results show that trained operators can perform the procedure with minimal systematic bias across boosters. The variability within booster varies considerably, with some boosters producing higher precision measurements due to the design of their belt-routing features. For any particular booster, the booster and dummy installation process accounts for about half the variability in the belt fit scores with the remainder due to variability in the belt routing and other measurement variability. Based on these findings, multiple measurements of belt fit in each booster are recommended to establish the desired level of confidence in the true belt fit. Straightforward statistical methods involving confidence intervals are recommended for establishing objective test methods. More testing will be needed to determine the reproducibility of the method across laboratories.National Highway Traffic Safety Administrationhttp://deepblue.lib.umich.edu/bitstream/2027.42/89866/1/102812.pd

Trapped Surfaces in Vacuum Spacetimes

An earlier construction by the authors of sequences of globally regular, asymptotically flat initial data for the Einstein vacuum equations containing trapped surfaces for large values of the parameter is extended, from the time symmetric case considered previously, to the case of maximal slices. The resulting theorem shows rigorously that there exists a large class of initial configurations for non-time symmetric pure gravitational waves satisfying the assumptions of the Penrose singularity theorem and so must have a singularity to the future.Comment: 14 page

Effects of vehicle features on CRS installation errors

This report documents a study of how vehicle features contribute to CRS installation errors. Thirty-two subjects were recruited based on their education level (low or high) and experience with installing CRS (none or experienced). Each subject was asked to perform four child restraint installations in three vehicles. Each subject first performed a CRS installation with a seatbelt in one vehicle, followed by three CRS installations using LATCH, one in each of three vehicles. One child restraint with a hook-on LATCH connector and one with a push-on LATCH connector were used. All installations were forward-facing, using an 18-month-old CRABI anthropomorphic test device (ATD). Six vehicles were used in testing, with half of subjects testing with each vehicle. Conditions were selected to provide a range of LATCH locations (visible, above seating surface, buried in bight), buckle stalk types (webbing vs. rigid), and tether locations (package shelf vs. seatback). After each installation, the experimenter evaluated 28 factors for each installation (such as tightness of installation, tether tightness, and LATCH belt attached correctly). Analyses used linear mixed models to identify the CRS installation outcomes associated with vehicle features. For LATCH installations, vehicles requiring higher forces to attach connectors to lower anchorages were more likely to be attached incorrectly. Vehicle seats with a bightline waterfall (which places the lower anchorage above the seating surface) increased rates of tight CRS installation for both seatbelt and LATCH installs. Seatbelt installations were tight (and locked) more frequently when the buckle stalk was located close to the bight rather than further forward. Subjects used the tether correctly in 30% of installations. Subjects used the tether more frequently during LATCH installations compared to seatbelt installations. The tether was used more frequently in sedans (with anchorage locations on the package shelf) than in vehicles with the tether anchorage located on the seatback. However, when the tether was used, it was routed correctly more often in vehicles with the tether anchorage on the seatback. A tether wrap around distance of 210 mm was sufficient to allow tightening of the tether with the two CRS tested, but additional testing showed that 5/16 CRS could not be tightened sufficiently with this wrap around distance. Installation time decreased with successive trials, but installation time was longer when subjects used the vehicle or CRS manuals. Subjects used the vehicle manual in 38% of installations, and were more likely to do so when the tether anchorage was located on the vehicle seatback. Subjects used the CRS manual in 88% of installations. In questionnaire responses, subjects indicated that the head restraints affected installations, and vehicle manuals varied in their ease of understanding. They also noted that tether anchorages on seatbacks were more difficult to locate than those on the package shelf. Results from this study do not fully support SAE and ISO recommendations for LATCH usability in vehicles. Recommendations areVTTI, National Highway Traffic Safety Administrationhttp://deepblue.lib.umich.edu/bitstream/2027.42/89862/1/102796.pd