Helmut T. Zwahlen

SAFETY ASPECTS OF SOPHISTICATED IN-VEHICLE INFORMATION DISPLAYS AND CONTROLS

Two groups of six young and healthy subjects were used in this study to investigate the lateral path deviations when driving in a straight path with the eyes fixated on the road ahead, when driving while reading information inside of the automobile, and when driving with the eyes closed. Each group of subjects drove a typical large car and a typical small car at a fixed speed of 30 mph. An unused 2000 foot long and 75 foot wide, level, concrete airport runway was used to conduct the experiment. Each subject made three runs under each of the three conditions with the large car and with the small car (18 runs total). The lateral path deviations from the longitudinal centerline of the car to the centerline of the runway were measured every 15 feet for a distance of 705 feet. A device which dripped liquid dye was attached to the center of the rear bumper of the automobiles to indicate their paths. The results of this study show that the average lateral standard deviations for driving with the eyes fixated upon the road ahead were between 5.5″ and 11.3″. The difference in the lateral standard deviations for large and small automobiles was statistically not significant for distances between 100 and 500 feet from the starting point for the three conditions tested. The lateral standard deviation was smaller for reading text within the automobile than for driving with the eyes closed, and was statistically significant after an occlusion distance of 225 feet or an occlusion time of about 5 seconds. Using a constant of 0.041, the fundamental relationship between the lateral standard deviation, the speed, and the occlusion distance developed by Zwahlen and Balasubramanian (1974) fits the data for reading text inside of the automobile while driving fairly well. This constant is approximately one half of that which has been used for driving with the eyes closed (0.076) in this study. Based upon the results of this study, the development and introduction of sophisticated in-vehicle displays and/or touch panels should be halted and their safety aspects with regard to information aquisition, information processing, and driver control actions should be critically evaluated.

VISIBILITY OF ROAD MARKINGS AS A FUNCTION OF AGE, RETROREFLECTIVITY UNDER LOW-BEAM AND HIGH-BEAM ILLUMINATION AT NIGHT

A study was conducted to obtain visibility data for old and young subjects performing a pavement marking end detection task on a fully marked road under headlamp illumination conditions. A total of 20 healthy subjects (10 old and 10 young) were used. It was found that observer age had a highly significant effect on pavement marking visibility. The effect of headlamp illumination (high-beam versus lowbeam) was found to be rather weak, probably because of the low-beam headlamp pattern, which favors the right-edge line. Pavement marking retroreflectivity was found to be significant at the levels investigated in the experiment. The new yellow dashed centerlines (tape) with a gapto-stripe ratio of 9.1/3 had a retroreflectivity of RL = 222 mcd/m2/lx and RL = 399 mcd/m2/lx under the medium and high conditions, respectively. The new white edge lines (tape) had a retroreflectivity of RL = 268 mcd/m2/lx and RL = 706 mcd/m2/lx under the medium and high conditions, respectively. The average end detection distances ranging from 124.8 m (average preview time 5.1 s for 88.5 km/h) for the old group under low-beam illumination on the medium retroreflectivity road to 237.3 m (average preview time 9.7 s for 88.5 km/h) for the young group under high-beam illumination on the high retroreflectivity road may appear to be rather long. However, the reader should be aware that markings as bright as the ones used in this research are the exception instead of the rule in real-world driving situations. The aim of this study was to determine the end detection distances obtainable under fairly favorable pavement marking material conditions.

Minimum In-Service Retroreflectivity of Pavement Markings

Minimum in-service retroreflectivity values for pavement markings are presented based on visibility computations performed with the CARVE (Computer-Aided Road-Marking Visibility Evaluator) computer model. CARVE accurately computes all geometric and photometric relationships for each headlamp separately; applies the human visual luminance contrast threshold database from Blackwell (Part III, 1946) adjusted by a field factor function that has been obtained from a number of pavement marking visibility field experiments; and provides retroreflectivity values for the pavement markings for any selected single-point geometry (e.g., ASTM 30-m geometry, observation angle = 1.05°, entrance angle = 88.7°). Based on the CARVE computation results, a set of in-service pavement marking retroreflectivity values are derived for fully marked, dark, straight, and dry roads using paint-and-beads pavement markings. The derived minimum retroreflectivity values for fully marked roads without raised pavement markers (RPMs) are highly speed dependent, because the computations are based on a constant minimum preview time of 3.65 s (3.0 s true preview and 0.65 s for eye-fixation duration). A separate set of minimum retroreflectivity values, based on a constant preview time of 2.0 s, is provided for fully marked roads with RPMs in good working order. It was found that the minimum retroreflectivity requirements for pavement markings could be substantially relaxed if RPMs (in good photometric working condition) were used. The proposed minimum retroreflectivity values are based on a 62-year-old driver (about the 85th percentile of the licensed driver population, about the 95th per-centile of the nighttime driver population based on trip frequency data as a function of the time of day).

Visibility of New Centerline and Edge Line Pavement Markings

The objective of the presented two-part study was to provide nighttime pavement-marking visibility data obtained under automobile low-beam illumination conditions in the field for further calibration of the Ohio University pavement-marking visibility model CARVE (Computer Aided Road Marking Visibility Evaluator). A total of 10 subjects participated in Part 1 of the study. The goal of Part 1 was to determine the end-detection distance of finite-length, new, medium-retroreflectivity, yellow pavement marking tape centerlines without edge lines as a function of the centerline configuration (single dashed, single solid, and double solid) and width. The results of Part 1 confirm that an increase in the average end-detection distance of about 55 percent represents the approximate upper limit of what can be achieved by adding more retro-reflective area to a yellow centerline. Part 2 consisted of four main experiments involving 10 subjects each and two follow-up experiments involving a total of 10 subjects. The goal of Part 2 was to provide pavement-marking end-detection distance data for fully marked roads consisting of left and right white edge lines with either a yellow double solid or single dashed centerline. The main effects of width, retroreflectvity, and centerline configuration were found to be statistically significant. A fully marked road consisting of both edge lines and a centerline generally appears to provide end-detection distances that are on average about twice as long as the end-detection distances that can be achieved with a centerline alone, without edge lines.

Driver-Headlamp Dimensions, Driver Characteristics, and Vehicle and Environmental Factors in Retroreflective Target Visibility Calculations

The inputs that are necessary for comprehensive visibility models are discussed. Inputs required by visibility models may deal with the physical arrangement of the observer and headlamps in three-dimensional space, the headlamp characteristics in terms of candlepower output and efficiency, observer age, observation time, probability of detection, and minimum preview time. There are also a number of environmental and vehicular parameters such as horizon sky luminance, atmospheric transmissivity, and windshield transmission. One problem associated with using comprehensive visibility models is the lack of standards, guidelines, and recommendations for the required model inputs. Consequently, it is currently difficult or even impossible to duplicate visibility model runs reported by others. Standardized headlamp-observer-target scenarios, standardized observer characteristics, and standardized environmental parameters would greatly facilitate cross-validation of model outputs. Numerous model input dimensions and values that are based on the technical literature are provided here. However, because there are no comprehensive eye location percentile dimensions available for late-model automobiles and for recent anthropometric dimensions, an exploratory vehicle survey was conducted and the measured vehicular dimensions were combined with anthropometric dimensions extracted from the 1988 U.S. Army personnel survey. The result of this effort is a table that shows the driver eye locations as a function of the population percentile, observer gender, and vehicle class. Further results include data pertaining to the location of low-beam headlamps. The recommended model input values should be considered for adoption as a standard that would facilitate easier cross-validation of visibility model results.

LEGIBILITY OF TRAFFIC SIGN TEXT AND SYMBOLS

An exploratory daytime and nighttime sign recognition and legibility field driving experiment involving 11 new reflectorized right-shoulder-mounted traffic signs and 10 young, healthy subjects (three replications) is described here. It was hypothesized that daytime conditions would provide longer recognition and legibility distances than nighttime conditions and that signs with bold symbols would provide longer recognition and legibility distances than textual signs. Also of interest was the formulation of the instructions to the subjects, which is likely to influence the legibility and recognition distances. Whereas other researchers have encouraged subjects to guess the symbols or legends, it was emphasized in the instructions of this experiment that the subjects were to say aloud the information on the traffic signs at that point during the approach when they could clearly (with near 100 percent certainty) identify all visual details of the message or the symbol. By comparing these results with the results of other studies, it was found that legend and symbol identification under clearly seen conditions provides legibility and recognition distances that are considerably shorter than those obtained if guessing is allowed. The average daytime legibility and recognition distances were about 1.8 times longer than the average nighttime legibility and recognition distances. It may be tentatively concluded that when reporting on field legibility research, it is of utmost importance to provide the reader with detailed information about how the subjects were instructed to respond to the stimuli (e.g., guessing was allowed versus clearly seen message). From the data obtained in this study, it appears that the effect of the subject instruction formulation is stronger under nighttime low-beam conditions than during daytime.

Driver preview distances at night based on driver eye scanning recordings as a function of pavement marking retroreflectivities

Pavement marking visibility models and tightly controlled pavement marking field experiments indicate that increased pavement marking retroreflectivity does in fact result in longer pavement marking visibility distances. The authors suggest that drivers should be provided with a pavement marking visibility distance long enough to allow for a preview time of 3.65 s at a given vehicle speed. This minimum required preview distance can be translated into a minimum required pavement marking retroreflectance. Questions were raised that perhaps drivers may not take advantage of brighter pavement markings (increased retroreflectance)—that is, drivers may not be looking as far ahead as possible from a pavement marking visibility point of view. This study was conducted to test whether drivers increase their longitudinal eye fixation distance when pavement marking retroreflectance is increased. Eye scanning data from six subjects were used to establish longitudinal eye fixation distributions on straight and level roads under low-beam illumination at night. In general, drivers appear to adjust their visual information acquisition behavior (longitudinal eye fixation distances and eye fixation preview times) when driving on roads with bright and highly visible pavement markings. Within the range of pavement marking retroreflectances investigated, it appears that, at least for half the drivers tested, brighter markings are indeed better and provide longer preview distances, which is desirable from an information acquisition, information processing, and safety point of view.

Evaluation of microwave radar trailers for nonintrusive traffic measurements

A trailer using two Wavetronix microwave radar units in side-fire mode was developed to measure traffic nonintrusively, including timestamped arrival records, moving average speed (N = 16), length, and classification (0 to 20 ft, 20 to 40 ft, more than 40 ft) of each vehicle. This paper reports on an initial validation of a prototype trailer on a fourlane section of US-50 east of Athens, Ohio. Traffic on the road was independently measured with video and radar, and the results were compared with records from the trailer to verify that the trailer was measuring the traffic with reasonable accuracy. The system records the arrival of more than 95% of all vehicles, with phantom and missed counts held to less than 5% in nearly all test cases. The overall average speed based on a 90-min time period is within 3 mph of the actual overall average values, although the observed standard deviation of the trailer moving average speed readings is about two to three times that of validation data, indicating that not all...

VISUAL DETECTION AND RECOGNITION OF FLUORESCENT COLOR TARGETS VERSUS NONFLUORESCENT COLOR TARGETS AS A FUNCTION OF PERIPHERAL VIEWING ANGLE AND TARGET SIZE

Daytime conspicuity of targets with fluorescent and nonfluorescent backgrounds as a function of the peripheral angle and the target size was investigated in the field. The resulting peripheral detection and recognition data may prove relevant to, for example, a bicyclist or a pedestrian approaching a driver at an intersection from a side street, or to a construction worker approaching a driver in a road construction site. Two groups of nine young, healthy subjects were used. White, blue, green, red, fluorescent red, fluorescent yellow-green, yellow, fluorescent yellow, orange, and fluorescent orange were presented at peripheral angles to the right of the line of sight. The targets were presented at a radial distance of 30 m (100 ft) from the front bumper of the car at the selected peripheral angle. The subjects were seated in a stationary car and the targets were visible for 2 sec. Each subject provided a total of 180 observations. The results of this study indicate that the fluorescent color targets (especially the fluorescent yellow-green) were considerably better-detected peripherally than their nonfluorescent counterparts. Furthermore, for some peripheral angles fluorescent yellow-green was among the top three best-recognized colors. On the basis of the results of this study, it may be concluded tentatively that to maximize daytime conspicuity for peripheral detection and recognition, highly conspicuous fluorescent colors such as fluorescent yellow-green, along with a fairly large target size, should be selected. It appears that however conspicuous a color is alone, if the target is too small for the visual angle subtended, the color will not be well detected or recognized, especially at larger peripheral viewing angles.

Approximated Headway Distributions of Free-Flowing Traffic on Ohio Freeways for Work Zone Traffic Simulations

Headway or interarrival time (IAT) data of successive vehicles in free-flowing traffic ahead of work zones for each lane on six different Ohio freeways (two with two lanes in one direction, three with three lanes, and one with four lanes) for 3 days were measured and analyzed. Approximated IAT distributions were generated as a function of the traffic volume for each lane, and relationships between traffic volumes and approximate cumulative IAT distributions were established; this allowed a direct conversion from hourly traffic counts to corresponding cumulative IAT distributions. On the basis of the validation of these IAT distributions with IAT data collected in an independent study, this conversion method produces fairly accurate cumulative IAT distributions for selected hourly traffic volumes. A set of cumulative IAT distribution spreadsheets may be downloaded at webce.ent.ohiou.edu/orite/cumulativeIATdistributions.html. It was also found that the same approximated cumulative IAT distribution can be used to model and simulate free-flowing traffic at other freeway locations in Ohio. It is not known whether these universal approximated IAT distributions would apply for freeways in other states.