Stacy A. Balk

Effects of Retroreflector Placement on the Nighttime Conspicuity of Pedestrians: An Open-Road Study

While considerable data indicate that positioning retroreflective markings on a pedestrians extremities can dramatically enhance nighttime conspicuity, most relevant safety devices (vests) limit coverage to the torso. We asked 120 participants to press a button whenever they recognized that a pedestrian was present during a short drive at night. A test pedestrian wearing different configurations of retroreflective markings was positioned on the left shoulder of an unilluminated two-lane roadway. Compared to an ANSI class-II vest alone, response distances were significantly greater when the vest was supplemented with ankle markings and when a full biological motion configuration was worn. Conspicuity was also greater when the pedestrian was walking and when facing the approaching test vehicle. Relative to a full eleven-element biological motion configuration, adding just two retroreflective ankle straps to a conventional safety vest is considerably more practical while still providing substantial conspicuity benefits.

Pedestrians' estimates of their own visibility at night are not reduced when headlights are severely weakened

Although it is clear that pedestrians typically overestimate how conspicuous they are to oncoming drivers at night, little is known about the factors that affect pedestrians’ estimates of their own conspicuity. This study explored the extent to which pedestrians judge that their own conspicuity is affected by headlight intensity and their clothing. Forty eight participants walked to and from a parked vehicle until they felt they were conspicuous to the driver. Unknown to the participants, headlight intensity was manipulated between subjects by filtering the vehicle’s high beams. Estimated recognition distances did not change with variations in headlight intensity even when up to 97% of the illumination from the headlights was blocked. This suggests that when pedestrians judge their own conspicuity they do not consider the magnitude of the headlight illumination that reaches them. Participants estimated that their recognition distances were only somewhat shorter when wearing black clothing relative to more reflective clothing. Together these findings underscore the need to educate pedestrians about their own nighttime conspicuity.

The (in)accuracy of estimations of our own visual acuity in the presence of glare

Headlights must balance two conflicting goals: maximizing visibility for the driver and minimizing glare to other drivers. Yet, recent increases in the number of complaints about headlights indicate a consumer focus on glare discomfort and not on poor visibility – a known causal factor of nighttime crashes. This study, as part of a series of experiments, explored the relationship between subjective and objective consequences of glare. Twenty-four participants used a psychophysically based technique to estimate their visual acuity in the presence of three different glare intensities. Actual acuity and subjective reports of discomfort were also assessed. Observers’ estimates of acuity significantly worsened as glare intensity increased, yet actual acuity was unaffected. Overall, estimates of the disabling effects of glare were more tightly correlated with subjective reports of glare-induced discomfort than with actual visual performance. These results, which are consistent with data obtained in the field – using vehicle headlights as the glare source – may help explain drivers’ reluctance to use their high beams. The results also underscore the need to collect data on disability glare, not just discomfort glare, when evaluating new lighting technologies.

Effects of Tire Pressure Monitoring Systems on Tire Pressures in Consumer Vehicles

In response to a federal mandate, all new light passenger vehicles in the United States will soon be required to include tire pressure monitoring systems (TPMSs) that alert drivers when one or more tires become 25% or more underinflated relative to the pressure level recommended by the vehicle manufacturer. Although the goal of TPMSs is to reduce the population of underinflated tires, their ultimate effect on tire pressure in consumer vehicles is unknown. Tire pressure and survey data were collected from approximately 1,200 vehicles that had just entered a rest area from an Interstate highway. Comparisons between vehicles with and without a TPMS were made from 864 vehicles in the full sample and from a subset of 123 target vehicles. The presence of TPMSs was generally associated with a small (0.7 to 1.5 psi) but significant decrease in the severity of tire underinflation. In addition, vehicles equipped with TPMSs were significantly less likely to have at least one tire that was 25% or more underinflated. The effect of TPMSs on tire pressure might have been larger had the systems been designed to activate at a less severe underinflation level. Less than 2% of survey respondents believed that TPMSs should have a trigger threshold as extreme as the currently mandated 25% threshold. Surveys also revealed that drivers without a TPMS do not report large differences in their tire maintenance behaviors relative to drivers with a TPMS and that more than 25% of drivers of vehicles with a TPMS are unaware that their vehicle is so equipped.

The accuracy of drivers' judgments of the effects of headlight glare on the visibility of a non-retroreflective object

Headlights must balance the conflicting goals of maximizing visibility for the driver and minimizing glare to others. Yet consumer complaints about headlights tend to emphasize only glare. This project extended earlier research by asking 17 young drivers to judge the distance at which they would be able to recognize the orientation of a non-retroreflective stimulus adjacent to the headlights of a stationary opposing vehicle. The beam setting (low vs. high) of both vehicles was manipulated. Participants correctly estimated that the stimulus would be less visible when their own vehicle used low beams and when the opposing vehicle used high beams. Contrary to earlier studies that used high contrast (retroreflective) stimuli, drivers’ estimates of conspicuity were, on average, not significantly different from the actual visibility of the stimulus. These results suggest that drivers’ understanding of headlight glare is more accurate for low contrast stimuli than for high contrast (retroreflective) stimuli and that drivers may overestimate the disabling effects of opposing headlights for higher contrast objects more than for lower contrast objects.

A Call to Classify and Quantify Hospital Medication Errors: Results from a Meta-Analysis

In 2000, the Institute of Medicine published To Err Is Human: Building a Safer Health System which stated that between 44,000 to 98,000 patient deaths occur annually due to largely preventable medical errors. While this number is staggering, the number of errors adversely affecting patients in ways other than death must be much greater. The goal of the current study was to determine the types of in-hospital drug-related medical errors that occur, as well as to quantify the proportion and severity of those errors. A lack of consistency across studies in hospital error reporting prevented an accurate analysis of drug-related errors and their severity. The authors recommend future studies (and hospitals alike) adhere to, at minimum, five guidelines in error reporting. It is hoped that with standardized reporting methods a better understanding of medication-related errors can be gained, thus resulting in the design and implementation of error-reducing measures.