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Technical Paper

Geometric Visibility of Mirror Mounted Turn Signals

Turn signals mounted on exterior rearview mirrors are increasingly being used as original equipment on passenger cars and light trucks. The potential for mirror-mounted turn signals (MMTS) to improve the geometric visibility of turn signals is examined in this paper. A survey of U.S. and UN-ECE regulations showed that the turn signals of a vehicle that is minimally compliant with U.S. regulations are not visible to a driver of a nearby vehicle in an adjacent lane. Measurements of mirror location and window geometry were made on 74 passenger cars and light trucks, including 38 vehicles with fender-mounted turn signals (FMTS). These data were combined with data on driver eye locations from two previous studies to assess the relative visibility of MMTS and conventional signals. Simulations were conducted to examine the potential for signals to be obstructed when a driver looks laterally through the passenger-side window.
Technical Paper

A Method for Measuring the Field of View in Vehicle Mirrors

A new method is presented for physically measuring drivers' field of view in rearview mirrors. A portable coordinate measurement apparatus (FARO Arm) is used to measure the mirror locations, contours, and curvature. Measurements of the driver's head and eye locations while looking into each mirror are also made. Raytracing is used to map the two- or three-dimensional field of view in each mirror. The method differentiates between monocular, binocular, and ambinocular fields of view, and can account for head movements. This method has been applied to passenger cars, light trucks, and heavy trucks to document how drivers aim their mirrors during normal use.
Technical Paper

Underride in Fatal Rear-End Truck Crashes

For the 1997 data year, UMTRI's Center for National Truck Statistics collected data on rear underride as part of its Trucks Involved in Fatal Accidents (TIFA) survey. Data collected included whether the truck had a rear underride guard, whether the striking vehicle underrode the truck, and how much underride occurred. A primary goal was to evaluate rear underride of straight trucks. Overall, 453 medium and heavy trucks were struck in the rear by a nontruck vehicle in a fatal crash in 1997. Some underride occurred in at least 272 (60.0%) of the rear-end crashes. For straight trucks, there was some underride in 77 (52.0%) of the crashes, no underride occurred in 43 (29.1%) of the fatal rear-end crashes, and underride could not be determined in the remaining 28 (18.9%) straight truck rear-end crashes. Despite the fact that three-fourths of tractor combinations had an underride guard on the trailer, underride was more common for tractor combinations.
Technical Paper

Development of an Improved Driver Eye Position Model

SAE Recommended Practice J941 describes the eyellipse, a statistical representation of driver eye locations, that is used to facilitate design decisions regarding vehicle interiors, including the display locations, mirror placement, and headspace requirements. Eye-position data collected recently at University of Michigan Transportation Research Institute (UMTRI) suggest that the SAE J941 practice could be improved. SAE J941 currently uses the SgRP location, seat-track travel (L23), and design seatback angle (L40) as inputs to the eyellipse model. However, UMTRI data show that the characteristics of empirical eyellipses can be predicted more accurately using seat height, steering-wheel position, and seat-track rise. A series of UMTRI studies collected eye-location data from groups of 50 to 120 drivers with statures spanning over 97 percent of the U.S. population. Data were collected in thirty-three vehicles that represent a wide range of vehicle geometry.
Technical Paper

Effects of Large-Radius Convex Rearview Mirrors on Driver Perception

The U.S. currently requires that reai-view mirrors installed as original equipment in the center and driver-side positions be flat. There has recently been interest in using nonplanar mirrors in those positions, including possibly mirrors with large radii (over 2 m). This has provided additional motivation to understand the effects of mirror curvature on drivers' perceptions of distance and speed. This paper addresses this issue by (1) reviewing the concepts from perceptual theory that are most relevant to predicting and understanding how drivers judge distance in nonplanar rearview mirrors, and (2) reviewing the past empirical studies that have manipulated mirror curvature and measured some aspect of distance perception. The effects of mirror curvature on cues for distance perception do not lead to simple predictions. The most obvious model is one based on visual angle, according to which convex mirrors should generally lead to overestimation of distances.
Technical Paper

Driver Perceptual Adaptation to Nonplanar Rearview Mirrors

This study examined perceptual adaptation to nonplanar (spherical convex and aspheric) rearview mirrors. Subjects made magnitude estimates of the distance to a car seen in a rearview mirror. Three different mirrors were used: plane, aspheric (with a large spherical section having a radius of 1400 mm), and simple convex (with a radius of 1000 mm). Previous research relevant to perceptual adaptation to nonplanar mirrors was reviewed. It was argued that, in spite of some cases of explicit interest in the process of learning to use nonplanar mirrors, previous research has not adequately addressed the possibility of perceptual adaptation. The present experiment involved three phases: (1) a pretest phase in which subjects made distance judgments but received no feedback, (2) a training phase in which they made judgments and did receive feedback, and (3) a posttest phase with the same procedure as the pretest phase.
Technical Paper

On-the-Road Visual Performance with Electrochromic Rearview Mirrors

This study was part of a series of studies on variable-reflectance rearview mirrors. Previous work included laboratory studies of human visual performance, field collection of photometric data, and mathematical modeling of the visual benefits of variable-reflectance mirrors. We extended that work in this study by collecting photometric and human-performance data while subjects drove in actual traffic. Three mirror conditions were investigated: (1) fixed-reflectance mirrors in the center and driver-side positions, (2) a variable-reflectance mirror in the center with a fixed-reflectance mirror on the driver side, and (3) variable-reflectance mirrors in both positions. The fixed and variable reflectivities were produced by the same mirrors by overriding the circuitry that normally controlled reflectance in the variable mode.
Technical Paper

Upper Extremity Injuries Related to Air Bag Deployments

From our crash investigations of air bag equipped passenger cars, a subset of upper extremity injuries are presented that are related to air bag deployments. Minor hand, wrist or forearm injuries-contusions, abrasions, and sprains are not uncommonly reported. Infrequently, hand fractures have been sustained and, in isolated cases, fractures of the forearm bones or of the thumb and/or adjacent hand. The close proximity of the forearm or hand to the air bag module door is related to most of the fractures identified. Steering wheel air bag deployments can fling the hand-forearm into the instrument panel, rearview mirror or windshield as indicated by contact scuffs or tissue debris or the star burst (spider web) pattern of windshield breakage in front of the steering wheel.
Technical Paper

Rearward Vision, Driver Confidence, and Discomfort Glare Using an Electrochromic Rearview Mirror

Electrochromic rearview mirrors can provide continuous levels of reflectivity and unobtrusive, automatic control. The availability of this technology has increased the importance of understanding how to select the best level of reflectivity for a given set of lighting conditions. For night driving with glare from following headlights, the best reflectivity level will always depend on a tradeoff among several variables. This study was designed to help clarify what variables are important and how they should be quantified. Twenty subjects, 10 younger and 10 older, performed a number of visual tasks while viewing stimuli through an electrochromic rearview mirror. Subjects were seated in an automobile mockup in a laboratory, and the reflectivity level of the mirror was changed before each of a series of discrete trials. On each trial, subjects saw reflected in the mirror a visual-acuity stimulus and a glare source of varying intensity.