Philip M. Garvey

AGE DIFFERENCES IN ESTIMATING VEHICLE VELOCITY

Automobile accidents among older adults may be related to difficulties in judging the speed of other vehicles. To examine this possibility, 3 groups of observers in the young adult, middle-aged, and older adult age ranges were asked to estimate the velocity of an isolated automobile traveling at 15-50 mph (24-80 kph). Across all age groups, perceived and actual velocity were related by a power function with an exponent of 1.36. Age was significantly and positively correlated with intercepts, but negatively correlated with exponents; that is, older observers showed less sensitivity to changes in actual velocity. Results bear on the issues of ontogenetic changes in accident involvement and sensitivity to motion.

EFFECTS OF FONT AND CAPITALIZATION ON LEGIBILITY OF GUIDE SIGNS

The research objective was to improve highway guide sign legibility by replacing the 40-year-old guide sign font with a new font called Clearview. It was believed that the current guide sign font’s thick stroke design, made with high-brightness materials and displayed to older vehicle operators, exhibited a phenomenon known as irradiation or halation. Irradiation becomes a problem if a stroke is so bright that it visually bleeds into the character’s open spaces, creating a blobbing effect that reduces legibility. The Clearview font’s wider open spaces allow irradiation without decreasing the distance at which the alphabet is legible. Results are presented of two daytime and two nighttime controlled field experiments that exposed 48 older drivers to high-brightness guide signs displaying either the current or the Clearview font. The Clearview font allowed nighttime recognition distances 16 percent greater than those allowed by the Standard Highway Series E(M) font, without increasing overall sign dimensions.

Age differences in Vistech near contrast sensitivity

ABSTRACT Contrast sensitivity was measured at near using the Vistech 6000 Contrast Test System (VCTS) in 287 persons aged 4 to 87 years. Obtained data compared well with those previously reported for the Vistech charts. Results indicate an age‐related loss in sensitivity to intermediate and higher spatial frequencies. This is consistent with the age trends observed using other methods for measuring contrast sensitivity functions (CSFs). However, the Vistech charts yield contrast sensitivity values which are lower than those obtained previously with the Nicolet system. These between‐method differences are greatest at lower spatial frequencies, and are attributed to the small number of grating cycles in the Vistech charts. The data are used to develop provisional age norms for the Vistech charts which allow the assessment of an individuals performance relative to their age cohort. Recommendations for use and future development of the Vistech charts are also given.

Guidance for the Design and Application of Shoulder and Centerline Rumble Strips

This report provides guidance for the design and application of shoulder and centerline rumble strips as an effective crash reduction measure, while minimizing adverse effects for motorcyclists, bicyclists, and nearby residents. Using the results of previous studies and the research conducted under this project, safety effectiveness estimates were developed for shoulder rumble strips on rural freeways and rural two-lane roads and for centerline rumble strips on rural and urban two-lane roads. The report will be of particular interest to safety practitioners with responsibility for roadway design.

MODEL GUIDELINES FOR VISIBILITY OF ON-PREMISE ADVERTISEMENT SIGNS

On-premise advertising signs play an important role in directing drivers. Well-placed and well-designed on-premise advertising signs can guide vehicle operators toward their destinations with minimal demand for attention. Poor placement of signs can sap a driver’s cognitive and perceptual resources, resulting in erratic maneuvers such as inappropriate slowing and lane changing. Increasingly, however, the visibility of on-premise advertising signs is being determined not by human factors researchers, visibility experts, or traffic engineers but by local planning and zoning officials, who lack specialized training in relevant fields. Regulations affecting on-premise sign visibility characteristics, such as means of illumination, lateral offset, and sign size, have been established mainly on the basis of arguments for improved aesthetic appeal and of vague, often unsubstantiated safety claims. There is a clear need to determine, from scientific and ergonomic perspectives, the effects these regulations have on sign visibility and traffic safety. An organized synthesis of existing literature on sign visibility based on 60 years of research and consisting of more than 150 journal articles and technical reports is presented. The synthesis may be used by sign designers to optimize the visual effectiveness of their signs. It also can provide a scientific basis for the development of new on-premise sign regulations or changes to existing regulations. A model set of guidelines for designing and locating on-premise advertisement signs for conspicuity and legibility is provided.

The effects of target borders on dynamic visual acuity: practical and theoretical implications

The effects of target borders on the ability of observers to resolve moving targets (Landolt Cs) under a range of conditions were examined. Contrary to reported findings with stationary targets, it was predicted that the presence of borders would improve acuity for slow-moving targets because (i) overall stimulus energy is kept relatively constant as target detail varies, and (ii) a low-spatial-frequency component is held constant as target detail varies. In an experiment in which a two-sided border (above and below the target) was used, the predicted beneficial effect of the border at slow speeds was obtained. The results are discussed in terms of practical implications for the assessment of dynamic visual acuity as well as the potential neural mechanisms underlying performance.

Letter Legibility for Signs and Other Large Format Applications

Numerous studies have evaluated the legibility of various fonts displayed in small print. There has also been a great deal of research into the legibility and recognition of standard highway sign alphabets. There has, however been no attempt to empirically determine large format distance legibility for the growing number of fonts currently available to non-transportation sign manufacturers. The present study systematically evaluated the letter legibility of a set of fonts that are consistent with commercial (e.g., storefront), industrial, transit, and highway signage. The fonts were evaluated in a laboratory setting. Individual test charts were designed for each of the fonts based on the standard Snellen distance visual acuity chart. Recognition acuity thresholds for each of the fonts yielded the minimum visual angle of letter height necessary for their resolution. The relative legibility of each font is discussed, as is the effect of font choice on sign size, and theoretical issues related to critical detail for letter recognition acuity.

Bandwidth of the contrast sensitivity function as an index of spatial vision with application to refraction

The contrast sensitivity function (CSF), although containing more information than traditional measures of acuity, has found difficulty gaining clinical acceptance. The hesitancy of clinicians to adopt the CSF stems, in part, from the fact that it is not as readily interpreted as is acuity. In order to facilitate such interpretation, five indices of spatial vision which are derivable from the CSF were examined in a sample of 287 persons aged 5 to 85 years. All indices were found to be both age-sensitive and strongly related to each other, but bandwidth of the CSF was chosen as a practical index for clinical settings. In a second study, acuity and CSF bandwidth were measured under 0 to ±1 D optical blur. It was found that the correction providing best acuity also maximized CSF bandwidth, and that bandwidth was more sensitive to optical blur than was acuity. Results support the assertion that CSF bandwidth is a readily interpreted index of spatial vision that can be measured efficiently within the context of clinical refraction.

Development of a New Guide Sign Alphabet

The research objective was to improve highway guide sign readability by replacing the current 40 year old guide sign font with a new font called Clearview. The rationale behind the research was the belief that the current guide sign font’s thick stroke design, when coupled with high brightness, results in a phenomenon known as irradiation, or halation. Irradiation becomes a problem when a character’s stroke is so bright that it bleeds into the character’s open spaces, creating a blobbing effect that reduces letter legibility. The Clearview font’s design was intended to widen the open spaces, thereby allowing irradiation without diminishing the distance at which the alphabet could be read. A controlled field experiment exposed older drivers to high-brightness guide signs displaying either the current or the Clearview font. Mean nighttime word legibility was improved by up to 22 percent, and mean word recognition distance increased by 16 percent with the Clearview font. In addition, the reading distance of words depicted in a standard highway all-uppercase font was compared with words shown in a mixed-case font; that is, with lowercase letters and an initial capital. In a legibility task, where individual letter reading is required, the larger uppercase letters resulted in greater legibility distances than those of the smaller mixed-case, but when the mixed-case font was increased in size so that mixed-case words used the same sign area as uppercase words, performance for the two was the same. When using word recognition as the dependent measure, where the task is discrimination of global word form, or “footprint,” the smaller mixed-case words were read at the same distance as the larger uppercase words. When the mixed-case font was increased in size so that mixed-case words used the same sign area as uppercase words, the mixed-case words were readable from significantly further away.

Development of an Open-Source Tractor Driving Simulator for Tractor Stability Tests

Developing devices for stability monitoring and rollover alerts is a promising possibility to prevent overturn events, which pose a severe risk to tractor operators. However, performing relevant tests with operators in the field is dangerous and impractical. As an alternative, this work identifies the challenges of simulating a tractor driving environment in a laboratory and details the solutions put in place to develop a tractor driving simulator at Penn State University. The simulator includes an instrumented tractor cab mounted on a custom motion base, a 2.43 m tall, 360° high-definition screen, a sound system, and a nine-computer network running open-source software that can be used to conduct experiments and simulate driving scenarios relevant to tractor instabilities. The system is used for an experiment that evaluates the drivers ability to perceive tilt angles at various tilt and roll combinations. Pilot-test results show that roll and pitch are systematically overestimated, producing perceptual errors that are unbiased, independent for roll and pitch, and typically have magnitudes of 4°. These results can aid the development of instability monitoring systems by considering human tilt perception to set alert thresholds. Future projects and applications of the tractor driving simulator are also discussed.