Fuat Aktan

Evaluation of Traffic Flow Analysis Tools Applied to Work Zones Based on Flow Data Collected in the Field

The Ohio Department of Transportation (ODOT) has identified the maintenance of traffic (MOT) as a top priority to serve the motoring public as part of a department strategic initiative. A key component of this strategy is to ensure that traffic flows efficiently through work zones. Work is described that was performed for ODOT to determine whether commercially available traffic simulation models could be calibrated to yield accurate queue length and delay time predictions for planning purposes in freeway work zones. Four work zones on multilane freeways were selected by ODOT for collection of the calibration data. Traffic flow video records were obtained at the four selected work zones by two ODOT video recording vans equipped with 15-m masts. Traffic flow parameters were extracted from the video records with the Mobilizer-PC software package. The traffic simulation and prediction tools investigated included the Highway Capacity Software (HCS), Synchro, CORSIM (under ITRAF and TRAFVU), NetSim, and a macroscopic model called QueWZ92. Simulation models were constructed with all models for the selected work zones, and the simulated queue lengths and delay times were compared with the data extracted from the field data with Mobilizer-PC. The results of this study indicated that the microscopic simulation packages could not be calibrated to the oversaturated conditions that existed at the work zones. The calibrated microscopic simulation packages underestimated the length of the queues that formed in the real world. The macroscopic QueWZ92 produced more accurate estimates than did the microscopic packages.

PERFORMANCE EVALUATION OF PAVEMENT MARKINGS UNDER DRY, WET, AND RAINY CONDITIONS IN THE FIELD

The nighttime visibility of three types of pavement markings—a largebeaded permanent pavement marking and two types of patterned pavement marking tapes, one with high-index beads and the other with mixed high-index beads—was evaluated under dry, wet (just after rainfall), and simulated rain conditions (ongoing 1-in./h rainfall). The dependent measures were pavement-marking end-detection distance and retroreflectance. The experiment was conducted at the 3M Transportation Research Center in Cottage Grove, Minnesota. This facility features a level and straight roadway section where 1-in./h rainfall can be simulated. Eighteen subjects between the ages of 55 and 75 participated in the study. The participants drove an experimental vehicle on dry and wet test sections with the pavement-marking treatments. Participants noted the earliest point at which they were able to see the end of the right edge line pavement markings. The retroreflectance of each pavement-marking material was also measured with three handheld retroreflectometers under the three weather conditions, according to ASTM E1710 (dry), ASTM E2177 (wet recovery), and ASTM E2176 (continuous wetting) standards. In terms of end-detection distances, the patterned tape with mixed high-index beads performed best under all three weather conditions. The paint and large-bead pavement markings were comparable to the tape with high-index beads under wet and rainy conditions. Under dry conditions, paint and large-bead pavement markings performed the worst. The detection distances seemed to strongly correlate with the standard retroreflectances only if the retroreflectance data from the corresponding test method are used.

TRAFFIC SIGN LUMINANCE REQUIREMENTS OF NIGHTTIME DRIVERS FOR SYMBOLIC SIGNS

An experiment was designed to determine the luminance contrast and background luminance requirements for recognition of negative contrast symbol signs (black on yellow) under low-adaptation luminance conditions. The effects of background complexity (two levels), symbol type (four symbols), background luminance (five levels), and luminance contrast between the symbol and its immediate sign background (six levels) were studied. The experiment was conducted in the Traffic Sign Simulator Facility of the Operator Performance Laboratory at the University of Iowa. Participants walked toward a calibrated, fixed-size sign stimulus projected on a large projection screen in the study. Two levels of performance were assessed: maximum recognition distance (threshold) and the distance at which the symbol types could be recognized with ease (confident). A total of 40 subjects, half of whom were young and half older, participated in the study. The traffic sign background luminance, luminance contrast, and symbol type were found to be statistically significant in affecting the symbol recognition distance. Observer age and background complexity were statistically nonsignificant. The difference between the threshold and confident viewing distances was also significant. The recognition performance data of four symbols is presented in terms of the visual angles subtended by the heights of the symbols for the six levels of contrasts and the five levels of background luminances.

Nighttime visibility and retroreflectance of pavement markings in dry, wet, and rainy conditions

Research was conducted to determine the nighttime visibility of flat pavement-marking tape, patterned pavement-marking tape, and wetweather pavement-marking tape in dry, wet (just after rainfall), and simulated rain conditions (ongoing 1-in./h rainfall). The measures of effectiveness were the detection distances, the eye-fixation distributions, and the pavement-marking retroreflectance. The research was sponsored by FHWA. The experiment was conducted on a test track in Cottage Grove, Minnesota. This test track had a section at which 1-in./h rainfall could be simulated. Eleven women and seven men, ranging in age from 55 to 74 (average age 62.5), participated in this study. The participants drove the experiment vehicles along the pavement-marking treatments. The participants were to state the earliest point at which they could see the end of the pavement markings. The retroreflectance of each pavement-marking material was measured with three handheld retroreflectometers under the three weather conditions according to ASTM E-1710 (dry), ASTM E-2177 (wet recovery), and ASTM E-2176 (continuous wetting). The retroreflectance values were correlated to the detection distances to determine the ability of each ASTM test method to predict visibility performance under the corresponding weather condition. The wet-weather tape performed best for detection distance, followed by the patterned tape and the flat tape. The detection distances were longest in the dry condition, shorter in the wet condition, and shortest in the simulated rain condition.

Review and Development of Recommended Minimum Pavement Marking Retroreflectivity Levels

Research was conducted to review and develop minimum levels for pavement marking retroreflectivity to meet nighttime driving needs. A previous study performed in the 1990s using a computer model called the Computer-Aided Road-Marking Visibility Evaluator resulted in a table of minimum levels of pavement marking retroreflectivity values that FHWA used to develop its initial set of minimum pavement marking retroreflectivity levels. Since then, additional research has been completed as well as development of a newer, more feature-intensive computer model called the Target Visibility Predictor (TarVIP). The research presented used TarVIP to study pavement marking retroreflectivity needs while using the most recently available information pertaining to driver, vehicle, and headlamp trends in the United States. In this research, previous pavement marking research efforts that included findings or recommendations related to minimum retroreflectivity are summarized. Next, a comprehensive survey on the factors that affect pavement marking visibility and minimum RL levels was performed, with key factors identified. They included pavement marking configuration, pavement surface type, vehicle speed, vehicle type, and presence of raised reflective pavement markers. From findings of the key factor reviews, the TarVIP model was used to generate preliminary results that could then be analyzed by sensitivity analysis. The research resulted in a set of recommended minimum pavement marking retroreflectivity levels for typical conditions on U.S. roadways. Limitations of the research were listed as well as concepts for future work.

Pedestrian Visibility Under Automobile Low-Beam Headlight Illumination: With and Without Headlight Covers

Pedestrians and bicyclists are the most vulnerable of all participants in traffic. Their safety at night should be a priority for headlamp designers, rule-making agencies, and consumers alike. A disturbing trend—the use of very dark aftermarket headlamp covers on vehicle headlamps—is emerging. This trend is observed primarily in sports cars owned by young drivers. These dark headlamp covers, often referred to as blackouts, serve no real purpose other than that of supposedly enhancing vehicle appearance. For a driver using such headlamp covers at night, it may appear as though the overall visibility is not much affected. However, this perception is misleading and wrong, as will be clearly demonstrated. The objective was to quantify the detrimental effects dark headlamp covers have on pedestrian visibility. To do so, detection distances were obtained in the field using 15 observers who were approaching stationary pedestrian mockups. The independent variables were pedestrian size (child, adult), diffuse clothing reflectance (dark, light), and illumination (with and without headlamp covers). Clothing reflectance turned out to have the strongest effect on the detection distance, closely followed by the factor of illumination. The conclusions that can be drawn from the work presented are simple. Nighttime pedestrians should not wear dark clothing, instead they should wear white or reflective clothing, and motorists should not drive with dark headlamp covers at night.

Tarvip, a PC-Based Visibility Model for Normal and Ultra-Violet Activated Pavement Markings

Development of TarVIP 1.0, a computer model for predicting the detection distances of normal and UV activated pavement markings was recently completed at the Operator Performance Laboratory (OPL). Two Sherwin-Williams UV activated pavement marking samples, four UV headlamp units (Ultralux, Visteon, Cibio and Labino brands), and the UV filter covering the Labino UV headlamp unit were characterized in terms of their fluorescence coefficients, spectral emissions, and spectral transmissivity, respectively. The TarVIP model properly accounts for a complete three-dimensional representation of the roadway-headlamp-driver geometry. Veiling luminance due to fog is modeled using the Mie Scattering theory. The model consists of physical and human performance subsystems. Besides the aforementioned physical subsystem items, the human performance subsystem uses an extensive human visibility contrast threshold database to represent the human capabilities and limitations of pavement marking detection. The model was used to obtain the visibility distances under various levels of fog density, UV activated pavement marking and UV headlamp efficiencies. The resulting visibility distances show some potential benefits and some inadequacies of the UV headlamps and UV activated pavement markings.

Nighttime Visibility of Prototype Work Zone Markings Under Dry, Wet-Recovery, and Rain Conditions

This paper presents the findings of a dynamic pavement marking visibility study conducted as part of the FHWA Highways for LIFE Technology Partnerships Program Temporary Wet-Weather Pavement Markings for Work Zones project. Three prototype optics-on-paint marking systems employing high refractive index dual-optics drop-on elements were evaluated at night under dry, wet-recovery (immediately after rainfall), and rain conditions. These three prototypes were chosen based on their durability from an initial pool of 22 experimental systems evaluated in a test deck. This dual-optic system was designed to provide good visibility in both dry and wet weather conditions. Two commercially available marking systems were also evaluated as industry benchmarks (one glass beads-on-paint system, one wet-reflective removable tape). Thirty participants driving through simulated work zones on a closed course viewed all of the marking types at night under all three weather conditions. Each drivers task was to identify the direction of work zone lane shift tapers delineated by the markings. In wet recovery, all three prototype marking systems and the wet-reflective tape sustained 60% to 80% of their dry average detection distances, and in rain, they sustained 50% to 70% of their dry average detection distances. In contrast, the average wet-recovery and rain detection distances for the conventional glass beads-on-paint benchmark system dropped to 28% and 17% of the dry detection distance, respectively. In addition, participants failed to detect the conventional glass beads-on-paint benchmark system in nearly half of the observations in the rain condition.