Reduced Visibility Conditions Research Articles

Enhancement of road delineation can reduce safety

BackgroundNew in-vehicle technologies often outpace the scientific support for their value. In lieu of valid and consistent scientific support, common wisdom is used, as in the assumption that enhanced roadway delineation improves driving safety. ObjectiveTo evaluate the effects of a Visibility Enhancement System that selectively improves lane markers' visibility on driving safety. MethodA simulation experiment assessed the effects of an in-car lane Visibility Enhancement System (VES) that highlights the edges of the road ahead on driver's behavior and overall safety, under normal and reduced visibility conditions. Thirty drivers drove in a fix-based simulator through a winding rural road, while attempting to avoid un-enhanced and unexpected obstacles that appeared on the driving lane from time to time. The simulated VES highlighted the road edges up to a distance of 90m with two alternative configurations: two continuous red lines or a series of red crosses. The effects of the two VES configurations on performance were measured during night and fog driving. Performance measures included speed, lane keeping behavior, eye scanning pattern, reaction time (RT) and collisions with the un-enhanced unexpected obstacles. Subjective measures included confidence and stress. Results: With the VES, drivers were more confident, less stressed, and drove faster, but had almost twice as many collisions with the unexpected obstacles. Also, steering/braking RT to the obstacles was longer with the VES than without it by nearly 44msec. ConclusionsThe results are consistent with Lebowitz's theory (1977). While the VES enhanced spatial orientation, it fooled the drivers into assuming that the visibility of obstacles on the road was also improved, and thus actually reduced safety. Practical Applications: When visibility is an issue in nighttime crashes, the site-specific crashes should be investigated, in cases of collision with objects-on-the-road, improved delineation should be ruled out.

Synthesis of State-of-the-Art in Visibility Detection Systems’ Applications and Research

Visibility is a critical component to the task of driving on all types of roads. The visibility detection and warning systems provide real-time, automated detection as well as appropriate responses to counteract reduced visibility conditions due to fog, heavy rain, snow, smoke, dust, or haze by informing drivers of present conditions and lowering the speed limits to match the reduced visibility condition. The objective of this research is to provide a synthesis of visibility detection systems and traffic control techniques that are developed and/or implemented in the United States and around the world. This article provides an overview of the best practices of fixed visibility systems at areas of recurrent dense fog and mobile systems for seasonal visibility reduction for areas of predicted seasonal fog or smoke from wildfires. Ongoing research efforts of developing new camera-based visibility detection systems are also discussed.

Daily shoaling patterns in the zebrafish Danio rerio

Abstract Shoaling intensity in zebrafish Danio rerio is believed to vary throughout subjective day and night hours. This experiment examines long term variations in shoaling behavior. Adult zebrafish Danio rerio were maintained under a 12:12 LD cycle (with dim red light serving as reduced visibility during subjective dark hours), and their shoaling behavior was monitored every hour for a three-day period of time. Our results show that zebrafish perform shoaling behavior throughout subjective day and under reduced visibility conditions, although mean shoaling times during the light phase were significantly higher than mean shoaling times during the dark phase. However, on the 3rd day of the experiment, mean shoaling times during the subjective night had increased and mean shoaling times during the subjective day had decreased. This shift in intensity was not seen on the first two days of the study, and may represent the influence of experience on the behavior of the test fish. We believe this study shows that shoaling behavior changes with light/dark cycles and that fish shoal even during reduced visibility conditions.

Evaluation of a Mobile Application for Multimodal Land Navigation

Among many of their countless dismounted roles, U.S. Air Force Battlefield Airmen must navigate in unfamiliar environments with many potential threats while performing their mission objectives. The effectiveness of navigating with a map and compass is compromised in reduced visibility conditions, such as in fog or during nighttime operations. Moreover, focusing on a map draws attention away from the immediate surroundings and reduces their ability to detect threats. To ameliorate this problem, we prototyped auditory and tactile navigation displays controlled only by a mobile phone using its built-in GPS and compass. The auditory and tactile displays direct users towards their destination with 3D audio and vibrotactile cues, respectively. We evaluated the navigation displays on a waypoint navigation task. Results suggest that auditory and tactile displays can guide users to their destination as effectively as a visual display (i.e., a GPS enabled map). Initial findings justify further development of multimodal navigation displays to increase the efficiency of Battlefield Airmen in land navigation tasks.

Predicting reduced visibility related crashes on freeways using real-time traffic flow data

ObjectivesThe main objective of this paper is to investigate whether real-time traffic flow data, collected from loop detectors and radar sensors on freeways, can be used to predict crashes occurring at reduced visibility conditions. In addition, it examines the difference between significant factors associated with reduced visibility related crashes to those factors correlated with crashes occurring at clear visibility conditions. MethodRandom Forests and matched case-control logistic regression models were estimated. ResultsThe findings indicated that real-time traffic variables can be used to predict visibility related crashes on freeways. The results showed that about 69% of reduced visibility related crashes were correctly identified. The results also indicated that traffic flow variables leading to visibility related crashes are slightly different from those variables leading to clear visibility crashes. Impact on IndustryUsing time slices 5–15 minutes before crashes might provide an opportunity for the appropriate traffic management centers for a proactive intervention to reduce crash risk in real-time.

Foggy perception slows us down

Visual speed is believed to be underestimated at low contrast, which has been proposed as an explanation of excessive driving speed in fog. Combining psychophysics measurements and driving simulation, we confirm that speed is underestimated when contrast is reduced uniformly for all objects of the visual scene independently of their distance from the viewer. However, we show that when contrast is reduced more for distant objects, as is the case in real fog, visual speed is actually overestimated, prompting drivers to decelerate. Using an artificial anti-fog-that is, fog characterized by better visibility for distant than for close objects, we demonstrate for the first time that perceived speed depends on the spatial distribution of contrast over the visual scene rather than the global level of contrast per se. Our results cast new light on how reduced visibility conditions affect perceived speed, providing important insight into the human visual system.DOI:http://dx.doi.org/10.7554/eLife.00031.001.

Age-related difference in steering control under reduced visibility conditions

The current study investigated age-related differences in a steering control task under low visibility conditions. Younger and older drivers were presented with displays simulating forward vehicle motion through a 3D scene of random dots on a ground plane. The lateral position of the vehicle was perturbed by a simulated side wind gust according to a sum of sinusoidal functions. The drivers’ task was to steer the vehicle to maintain a straight path. The visibility of the driving scene was reduced by reducing the quantity and the quality of the optical flow field. We found that performance decreased when visibility was reduced for both older and younger drivers, with better performance for younger drivers as compared with older drivers. An age-related interaction was also found with deteriorated optical flow information. These results suggest that under reduced visibility conditions, older drivers may have increased accident risks due to decreased ability to successfully steer the vehicle.

Istical Characterization of Aerosols' Liquid Water Content and Visibility for Terrestrial FSO Links

Liquid water content (LWC) is a microphysical parameter which is used to characterize fog/cloud and other particulates. In the absence of precipitation higher amount of LWC depicts dense fog, significantly reducing visibility and causing performance degradation of free-space optical (FSO) links for a non-negligible amount of time. A measurement campaign in Prague (Czech Republic) has recorded the specific attenuation caused by fog in terrestrial FSO links along with visibility, liquid water content (LWC) and integrated particle surface area (PSA) for operational wave-lengths of 1550 nm and 830 nm (installed at two different path links). This contribution presents and analyzes 5 months real time measured data of LWC and visibility for terrestrial FSO links in an attempt to find the best fit distribution model for aerosol's liquid water content and visibility for terrestrial FSO links under reduced visibility conditions. The Probability Density Function (PDF) estimation ofvisibility and LWC puts forth the Gamma distribution as the best fit distribution for both. The results provide the statistical behaviour of LWC and visibility, which is of high importance for Optical Wireless systems and networks.

Driver Behavior and Preferences for Changeable Message Signs and Variable Speed Limits in Reduced Visibility Conditions

This article investigates the factors affecting drivers’ stated behavior in adverse visibility conditions and examines whether drivers rely on and follow advisory or warning messages displayed on portable changeable message signs (CMS) and/or variable speed limit (VSL) signs in different visibility and traffic conditions, and on two types of roadways: freeways and two-lane roads. A multiple-approach survey was designed to collect opinions and stated data from Central Florida drivers. Categorical data analysis techniques such as conditional distribution, odds ratio, and chi-squared tests were applied. In addition, two modeling approaches, bivariate and multivariate probit models, were estimated. The results revealed that gender, age, road type, visibility condition, and familiarity with VSL sign were the significant factors affecting the stated likelihood of reducing speed following CMS/VSL instructions in reduced visibility conditions. Other objectives of this study were to determine the content of messages that would achieve the best perceived safety and drivers’ compliance and to examine the best way to improve safety during these adverse visibility conditions. The results indicated that respondents thought that “Caution–fog ahead–reduce speed” was the best message and that using that CMS and VSL signs together was the best way to improve safety during such inclement weather situations. Based on the findings of the present study, several recommendations are suggested as guidelines to improve safety in reduced visibility conditions.

Analysis of drivers’ behavior under reduced visibility conditions using a Structural Equation Modeling approach

One way to improve safety under reduced visibility conditions (i.e., reduce the chances of visibility related crashes) is to improve drivers’ behavior under such adverse weather conditions. The aim of this paper is to thoroughly examine drivers’ responses under low visibility conditions and quantify the impacts and values of various factors found to be related to drivers’ compliance and drivers’ satisfaction with variable speed limit (VSL) and changeable message signs (CMS) instructions in different visibility, traffic conditions, and on two types of roadways; freeways and two-lane roads. The data used for the analyses were obtained from a self-reported questionnaire survey carried out among 566 drivers in Central Florida, USA. To achieve these goals, Explanatory Factor Analysis (EFA) and Structural Equation Modeling (SEM) approaches were adopted. The results revealed that drivers’ satisfaction with VSL/CMS was the most significant factor that positively affected drivers’ compliance with advice or warning messages displayed on VSL/CMS under different fog conditions followed by human factors. Moreover, it was found that roadway type affected drivers’ compliance to VSL instructions under medium and heavy fog conditions. Furthermore, drivers’ familiarity with VSL and human factors were the significant factors affecting drivers’ satisfaction with VSL/CMS advice under reduced visibility conditions. Based on the findings of the present study, several recommendations are suggested as guidelines to improve drivers’ behavior in such reduced visibility conditions by enhancing drivers’ compliance with VSL/CMS instructions.

Systemic accident risk assessment in air traffic by Monte Carlo simulation

A systemic accident model considers accidents as emergent phenomena from variability and interactions in a complex system. Air traffic risk assessments have predominantly been done by sequential and epidemiological accident models. In this paper we demonstrate that Monte Carlo simulation of safety relevant air traffic scenarios is a viable approach for systemic accident assessment. The Monte Carlo simulations are based on dynamic multi-agent models, which represent the distributed and dynamic interactions of various human operators and technical systems in a safety relevant scenario. The approach is illustrated for a particular runway incursion scenario, which addresses an aircraft taxiing towards the crossing of an active runway while its crew has inappropriate situation awareness. An assessment of the risk of a collision between the aircraft taxiing with an aircraft taking-off is presented, which is based on dedicated Monte Carlo simulations in combination with a validation approach of the simulation results. The assessment particularly focuses on the effectiveness of a runway incursion alert system that warns an air traffic controller, in reducing the safety risk for good and reduced visibility conditions.

A user-centred approach for designing driving support systems: the case of collision avoidance

The work described in this paper is focused on an approach for implementing in real working contexts the guidelines of user-centred design contained in formal standards and in many research studies. The application concerns the EUCLIDE project (enhanced human–machine interface for on vehicle integrated driving support system), which aimed at developing a driving support system to avoid collisions with obstacles in reduced visibility conditions. The design of the system followed a user-centred approach which started by identifying the model of cognition to be applied throughout the whole design process. The definition of the warning strategies of the system was firstly analysed with the aim to achieve the highest balance between a totally supportive system and a non-disturbing system. Then an initial set of design solutions for the human–machine interface was tested in a static driving simulator. A second set of possible interfaces was evaluated in a dynamic simulator before developing a final design. This solution was implemented in two real vehicles and tested in real traffic situations. This paper describes the whole design process and concentrates on the final step of “in-vehicle” integration process. The road tests performed at the end of the whole process are discussed in detail focusing on the safety implications associated with the design solution finally selected and implemented.

The influence of high contrast acuity and normalised low contrast acuity upon self-reported situation avoidance and driving crashes.

The aim of this study was to determine the cues used to signal avoidance of difficult driving situations and to test the hypothesis that drivers with relatively poor high contrast visual acuity (HCVA) have fewer crashes than drivers with relatively poor normalised low contrast visual acuity (NLCVA). This is because those with poorer HCVA are well aware of their difficulties and avoid dangerous driving situations while those poorer NLCVA are often unaware of the extent of their problem. Age, self-reported situation avoidance and HCVA were collected during a practice based study of 690 drivers. Screening was also carried out on 7254 drivers at various venues, mainly motorway sites, throughout the UK. Age, self-reported situation avoidance and prior crash involvement were recorded and Titmus vision screeners were used to measure HCVA and NLCVA. Situation avoidance increased in reduced visibility conditions and was influenced by age and HCVA. Only half of the drivers used visual cues to signal situation avoidance and most of these drivers used high rather than low contrast cues. A statistical model designed to remove confounding interrelationships between variables showed, for drivers that did not report situation avoidance, that crash involvement decreased for drivers with below average HCVA and increased for those with below average NLCVA. These relationships accounted for less than 1% of the crash variance, so the hypothesis was not strongly supported.

The Role of Landmark Information in Intelligent Navigation Displays

Advanced Traveler Information Systems (ATIS) are advanced communication and navigation systems that use computer-based in-vehicle systems to provide navigation and travel-related information to drivers. To help drivers navigate effectively and get to their destinations quickly and safely, navigational information must be effectively communicated to the driver. Landmarks are important environmental and navigational cues that help drivers to get to their destinations. This paper describes a study that tested the influence of landmark information in route guidance displays on navigation performance in a simulated driving environment. Forty-eight participants drove in a high-fidelity simulator and navigated using route guidance displays with and without landmark icons. The results indicated that landmarks were beneficial as a navigation aid; they helped drivers make turning decisions more quickly, especially in reduced visibility conditions (i.e., foggy conditions). Landmarks were particularly beneficial to older drivers by improving their turning accuracy and turn signal accuracy, especially in the fog.

Strategic adaptations to lack of preview in driving

Two experiments were carried out in a driving simulator in order to study driving behaviour in reduced visibility conditions. Both studies show that drivers maintain larger time headways when preview is limited. The results suggest that the adaptation of time headway was related to difficulty of anticipation rather than perceptual degradation due to reduced visibility. Drivers who were instructed to drive on a fixed time schedule did not increase their time headway in adverse visibility circumstances. However, they reacted very accurately to decelerations of lead cars, which prevented the occurrence of critical situations. In general, the results indicate that drivers apply a hierarchy of adaptive strategies which are aimed at the control of time pressure in driving. In normal visibility conditions, drivers adopt an anticipatory driving strategy. When the possibilities for anticipation are reduced, drivers compensate by means of speed reductions and increases in time headway, in order to increase the time available to react to potential threats. When this compensatory strategy is impossible or undesirable, drivers have to maintain high alertness in order to react accurately to unpredictable hazardous events. This strategy imposes a high time pressure on the driver. Presumably, drivers try to restrict time pressure and therefore the effort costs of driving when they have the opportunity to do so.

Advanced Taxi Map Display Design for Low-Visibility Operations

Conducting gate to gate operations during reduced visibility conditions is a major impediment to scheduled and unscheduled flight operations in the National Airspace System (NAS). Takeoff and landing minima are predicated on aircraft equipage and airport visibility (e.g., at some major airports, operations are terminated when visibility is below 700 ft runway visual range (RVR). Although some aircraft can land with zero-zero visibility, there are no ground or flight deck systems that allow them to taxi under low visibility conditions. A map display system designed to support low visibility taxi was evaluated by 12 B-747 flight crews in NASA's Crew Vehicle System Research Facility (CVSRF). Three taxi-map conditions were compared: paper map only, basic moving map, and advanced moving map. Crews landed and taxied along 24 different taxi routes under three visibility conditions: unlimited visibility, 700 ft RVR, and 300 ft RVR. Taxi time, errors and workload were collected for each taxi operation. Video tape recordings captured crew interactions and head-up and head-down times. Taxi times and errors were significantly better for crews with electronic maps than for crews with a paper map. Although crews with the advanced map experienced significantly more head-down time, the head down interval was significantly less than with the paper map and crew workload was significantly less. During the post-flight design review, pilots identified improvements in procedures and formatting that might enhance performance. They developed a procedure for safely switching from the NAV display to the map; and in general their comments were very favorable.

SUBJECTIVE EVALUATION OF DRIVER'S EYE-MOVEMENT DURING BLOWING SNOW

This paper describes evaluation of driver's eye-movement in reduced visiblility conditions due to blowing snow. Driver'eye-movement is evaluated by following methods.(1) Fixation duration, angular velocity, three-dementional coordinatesand frequency distribution of fixation points in reduced visibility conditions are estimated from driver's fixed points.(2) Driver's visual field under blowing snow condition can be defined by the concept of ‘Fuzzy’. We tryto estimate driver's eye-movement behavior by use of a ‘Fuzzy Entropy’, which is the expectation of an amount of information.

Double-ended lidar technique for aerosol studies

The technique of inverting a single-ended lidar return to obtain range-dependent atmospheric extinction coefficients requires an assumption concerning the relationship between the volumetric backscatter and extinction coefficients. By comparing the powers returned from a volume common to each of two lidars located at opposite ends of a propagation path the need for this relationship can be eliminated, and the extinction coefficient is determined as a function of position between the two lidars. If the lidars are calibrated, the backscatter coefficients and their relationship to extinction can then be determined as a function of position. We present measurements obtained with two lidars which were operated reciprocally over a slant path of ~1 km during reduced visibility conditions. The measured extinction and backscatter coefficients determined by this method provide the boundary value inputs to both the forward and reverse integration algorithms for inverting the single-ended lidar returns. The accuracies by which both singleended integration schemes can reproduce the double-ended measurements are examined by allowing the ratio of backscatter to extinction coefficients to be either constant or varying with position between the two lidars as measured.

Visibility changes caused by St. Louis

Locally generated pollutants at St. Louis markedly reduce surface visibility in summer. Reductions occur in all hours, and are most evident in the city which has a 33 % increase in the frequency of conditions defined as reduced visibility (< 9.6km). Under most wind conditions reduced visibilities extend 30–50 km beyond the city, but principally during daylight hours when reduced visibility conditions occur two or three times more often than expected. During the nocturnal hours the visibility reduction tends to be greatest in the city.