Sight Distance Research Articles

Multivariate models to investigate the relationship between collision risk and reliability outcomes on horizontal curves

This paper proposes a reliability-based framework to address the risk associated with limitations in the Available Sight Distance (ASD) on curved highway segments considering a three-dimensional (3D) sight distance computation approach. To facilitate this assessment, the ASD on horizontal curves was evaluated and an accurate inventory of curve attribute information was generated using LiDAR (Light Detection and Ranging) data in an automated and efficient manner. These datasets were then used to estimate the risk (probability of noncompliance, Pnc) associated with sight distance insufficiencies. Full Bayes multivariate Poisson log-normal safety performance functions were developed to relate the Pnc to the expected number of collisions. The results show that there was a statistically significant relationship between Pnc and collision frequency. There was also a significant correlation of 0.444 to 0.452 across collision severity levels indicating that curves with high Property-Damage-Only (PDO) collisions could be associated with higher injury and fatal (I + F) collisions. It was also found that Pnc had a greater impact on increasing PDO collisions than I + F collisions, suggesting that collisions associated with insufficient sight distance are likely to be less severe. The results of this analysis are expected to improve our understanding of the risks associated with deviations from design guidelines and quantitatively assess the safety margins due to these variations. The framework presented in this paper can be used to compare different design alternatives and investigate the influence of design deficiencies on collision occurrence across various severity levels.

Reliability Analysis of Intersection Sight Distance at Roundabouts

This paper presents a reliability-based method for the design of intersection sight distance (ISD) at traffic roundabouts using the linear and nonlinear deceleration profiles of the entry vehicles. The reliability method is based on the first-order second moment method which is simple and relatively accurate compared with advanced methods. The nonlinear deceleration profile includes a shape parameter that produces the linear profile as a special case. Deterministic and reliability-based formulas for the required ISD for an approaching vehicle are developed for the entry vehicle on the left and the vehicle on the circulating roadway. Then, the design values of the ISD legs, applicable to any type of roundabout, are presented for different probabilities of non-compliance (Pnc) and different coefficients of variations. For the special case of single-lane symmetrical roundabouts, which have a well-defined geometry, the lateral clearance needs are established. The sensitivity analysis shows that ISD is very sensitive to both the mean and variance of the critical headway. The results show that the deterministic method results in ISD values that correspond to a very small Pnc, indicating that the method is very conservative. The proposed method, which provides flexibility in selecting ISD for any given Pnc, should be of interest to highway designers and practitioners to promote roundabout safety.

Quantification of surrogate safety measure to predict severity of road crashes at median openings

Traffic safety assessment is an integral part of transportation engineering. In a developing country like India, it is observed that in every four second, one person gets injured in road crashes. Moreover, at median openings which are usually uncontrolled in India, the severity of road crashes increase many fold. This is due to the fact that neither lane discipline nor priority rule is followed at the median openings. Conventionally, road crash data reports were used to study and analyze traffic safety. However, the drawback of this traditional method is that a lot of accidents need to be recorded for analysis and to draw any conclusions and take necessary corrective measures. In developing countries like India, available accident data are based on reports submitted by the police department of respective state governments. The accuracy of these accident data details is highly questionable. Therefore, in the recent times surrogate traffic safety measures are being used to analyze traffic safety. Various surrogate traffic measures like Deceleration Time (DT), Time to Collision (TTC), Post Encroachment Time (PET), etc. are being used to examine road safety. These values are based on the temporal and spatial proximity between road-users during possible conflict situation. Among all the traffic safety measures, PET is regarded as the most reliable and most commonly used indicator. Therefore, in this study, PET across different traffic volume levels at median opening area is calculated. A critical safe ratio has been introduced to better analyze the traffic safety at median opening based on minimum stopping sight distance (SSD) as per IRC: 66–1976 and speed to PET ratio. Finally clustering technique has been used to define various severity indices for probable road crashes at median opening area. For this study, data has been collected from different median openings located on six-lane divided urban roads.

Modeling and interpreting road geometry from a driver's perspective using variational autoencoders

AbstractQuantitative description of perspective geometries is a challenging task due to the complexities of geometric shapes. In this paper, we address this gap by proposing a new methodology based on variational autoencoders (VAE) to derive low‐dimensional and exploitable parameters of the perspective road geometry. First, road perspective images were generated based on different alignment scenarios. Then, a VAE was built to create a regularized and exploitable latent space from the data. The latent space is a compressed representation of perspective geometry, from which six latent parameters were derived. Without prior expert knowledge, four of the latent parameters were found to represent distinctive attributes of the geometry, such as visual curvature, slope, sight distance, and curve direction. The latent parameters provided quantitative measurements of how the design scheme looks like in perspective view. It was found that a road with low accident rate has low values for codes 4 and 5, high values for code 3, and low variance for codes 3 and 6. The trained VAE model also ensured accurate generation of the perspective images by decoding the latent parameters. Overall, this research advances the understanding of road design by considering the driver's perception.

Visual Perception Adaptive Image Processing for HD Microdisplay

With the development of 5G networks, a new wave of development is ushered in the field of virtual reality (VR). The small physical size, lightweight, low power consumption, and high brightness make microdisplays the core components of VR. In order to improve the user's immersive experience and reduce the screen window effect, microdisplays are required to have higher pixel density and faster refresh speeds. However, this demand results in a large amount of data transmission and poor real‐time rendering of image information. When the human eye observes an image, the gaze point changes due to the interest of the viewer. To solve this problem, we propose an image compression algorithm based on visual perception adaptation to reduce data transmission bandwidth. The experimental results show that when sight distance is 2, the maximum comprehensive compression ratio is 42.834, the minimum comprehensive compression ratio is 11.415, the minimum clock frequency is 17.033MHz, and the maximum clock frequency is 63.916MHz. The algorithm effectively reduces the data transmission bandwidth and meets the real‐time rendering of VR application, and the rendering effect is good.

Calibrating Design Guidelines using Mental Workload and Reliability Analysis

The generic nature of road design is indiscriminate to age, race, or gender, as it is implicitly assumed that there are few behavioral differences between drivers while traversing various alignment elements (e.g., horizontal curves, tangential segments, etc.). For instance, the perception reaction time required, which is based on an 85th percentile value, on a tangent section is the same as that on a horizontal curve. This suggests that current guidelines do not consider the complexity that some geometric features might induce on drivers, and consequently, there is a need to address the many considerations of diversity. In this respect, human factors should be explicitly included in design guidelines. One aspect of human factors that has received little attention in the literature is related to the mental workload. In this study, a procedure is presented to estimate the mental workload for stopping sight distance. Then, reliability analysis is conducted to compare the change in the probability of non-compliance owing to the available sight distance and based on the mental workload. By analyzing data from 12 horizontal curves in Alberta, Canada, the probability of non-compliance dropped from 9.1% to 0.7%, and a moderate correlation with collisions was found. The results of the analysis showed that incorporating mental workload into the geometric design process can improve safety performance.

Vehicle energy savings by optimizing road speed-sectioning

In a context of decreasing resources and of climate change, lowering road vehicles consumption is a key point to meet CO2 reduction requirements. In addition to car technological advances, eco-driving is part of the solution but the road infrastructure should ensure its development. This work aims to demonstrate that road energy demand and associated pollutant emissions can be reduced by working out minor optimization of road infrastructure itself. For this to happen, a simple eco-driving potential criterion is built upon infrastructure parameters such as slopes and sight distances. This criterion aims to detect Misplaced Speed-sectioning Positions (MSP) with regard to the Starting Point of Deceleration (SPD); with speed-sectioning being the succession of speed changes along a given route. An enhanced energy waste formulation is then developed to quantify the vehicles energy waste due to misplaced road-signs. Thirdly, a traffic simulation constitutes a framework for energy evaluation; considering a full flow of vehicles, based on real traffic data, and by modeling several driver behaviors. Simulation results show that a significant fuel reduction of up to 5.5% can be achieved locally, simply by moving a road sign, for rural areas and without degrading road safety.

Reliability-Based Design for Passing Maneuvers Based on Observational Data

Two-lane roadways constitute the largest proportion of road networks. Their operational characteristics are significantly different from other road classifications. Allowing passing maneuvers is considered as one of the effective measures to improve mobility levels along two-lane highways, while crash records show that head-on collisions, which usually are attributed to passing maneuvers, are among the most common and most severe types of crashes on two-lane roadways. Therefore, rational and realistic estimation of the needed passing sight distance (PSD) considering driver behavior is essential for the safe design of passing zones along two-lane highways. Several random variables help to determine the minimum length required for safe passing maneuvers. Current PSD models are based on single deterministic values of the input variables to determine PSD values. This paper presents a reliability model PSD that accounts for the variability of the input random variables to offer a better representation of real-life conditions. The objectives of this paper are: (1) to design driving simulator and field experiments for data collection, (2) to develop a PSD model using the mechanics of passing maneuvers, (3) to develop a reliability model based on the first-order second-moment (FOSM) method, and (4) to validate the model using Monte Carlo simulation. In this study, driving simulator experiments were conducted to determine the passing behavior of drivers, and field data were used to validate the proposed PSD model. The proposed model accounts for the variability in the parameters by using the mean and standard deviation in a closed form estimation method. The analysis was performed for a design speed of 80 km/h, and the corresponding PSD distribution was established. A comparison of the results of the proposed model, which reflects driver behavior, and those of existing models was presented. Using the reliability-based design method, transportation engineers can adjust the PSD to fulfill a desired probability of non-compliance.

Determination of the Existing Sight Distance and its Influence on the Speed on Highways

The main task of a high-quality road design is to provide the driver with a clear information about the course of the road at an early stage. The good visual guidance on highways is a prerequisite for adequate driving safety. Therefore, the sight distance has a significant impact on traffic safety, performance, speed behavior and driving comfort. At least the required stopping sight distance should always be guaranteed on highways, in order to ensure traffic safety and quality of traffic flow. The purpose of the stopping sight distance is to enable the driver to stop in time in front of an unexpected obstacle with a certain height on the road or in front of the end of a traffic jam. In addition, as a regulating element in road design, it is intended to ensure early driver information and orientation. The driver reacts to external influences by choosing the speed and changing it. Therefore, the speed parameter itself represents the best and most suitable evaluation criterion for driving behavior. In this paper, it has been succeeded to prove, that the existing sight distance exerts an influence on the speed on highways in Germany. A clear increase in the 85th percentile speed was determined with an increasing existing sight distance up to 400 m. At a sight distance above 400 m V85 remained almost constant. An increase in the 15th percentile speed was only noticeable up to a sight distance of 300-350 m, after which V15 remained at the same level.

The CN Lantern Test and Different Viewing Distances.

This research shows that some color-vision-defective patients could identify railway signal lights correctly if they are working in the yard where sighting distances for signal lights are shorter. When interpreting railway signal lights, sighting distance can vary depending on the employee's location and job requirements. Individuals with a color-vision-defect may pass railroad employment color vision testing for positions with shorter sighting distances, despite failing to qualify for positions with longer sighting distances. The CN Lantern (CNLan) simulates railway signal lights. We evaluated performance and repeatability on CNLan at different viewing distances in color-normal and color-deficient individuals. Fifty-six subjects with normal color vision and 63 subjects with a red-green color-vision-defect participated. The CNLan test was performed at 4.6-, 2.3-, 1.15-, and 0.57-m viewing distance. The test was repeated after 10 days. All individuals with normal color vision passed the CNLan at all distances at both visits without errors. For the group with a color-vision-defect, the pass rate increased from 12% at 4.6 m to 62% at 0.57 m. The repeatability of the CNLan between visits for the color-vision-defective group was very good with AC1 agreement values greater than 0.85. An increase in retinal illumination was likely responsible for the improved performance as the test distance was decreased. Typical sighting distances in railway yards correspond to the 0.57-m test distance in our study. The results of this study suggest that 62% of the individuals with a red-green color-vision-defect may correctly identify colored signal lights in a railway yard where sighting distances are less than 100 m.

Voxel-Based Methodology for Automated 3D Sight Distance Assessment on Highways using Mobile Light Detection and Ranging Data

Ensuring that the available sight distance (ASD) on highways meets the minimum requirements of geometric design standards is crucial for safe and efficient operation of highways. Current practices of ASD assessment using design software or through site visits are labor intensive, time consuming, and traffic disruptive. Thus, this paper introduces a fully automated algorithm that allows large-scale assessment of ASD in three-dimensional (3D) space on highways utilizing mobile light detection and ranging (LiDAR) data. The algorithm was tested on LiDAR data of highway segments in Alberta, Canada. The results showed that the algorithm was highly accurate in detecting sight distance limitations at the defined regions and, in all cases, the driver’s vision was restricted by the pavement surface on vertical crest curves. In the case of combined vertical and horizontal curves, the vertical crest curve was found to be the controlling element in sight distance deficiencies. In addition, the assessment of historical collision data revealed clusters along the regions defined with ASD limitations, indicating that restrictions in drivers’ vision could have contributed to the collision occurrence.

Influence of Night Rainfall on Stopping Sight Distance on Dark Roadways

Aim: To investigate the influence of night rainfall on stopping sight distance on dark roadways. Background: This study fills the research gap in stopping sight distance by looking at night rainfall impact on stopping sight distance on dark roadways. Objectives: To determine stopping sight distance under night rainfall (light, moderate and heavy) on dark roadways and compare the results with stopping sight distance under dry night on dark roadways. Methods: In a ‘with and without’ night rainfall impact studies, traffic volume, speed, vehicle type and rainfall data were collected at selected sites. All surveyed sites had rain gauge within the catchment area of about 1km. Rainfall intensity was divided into three groups (light, moderate, and heavy). Dry weather data were used as a control parameter. Results: Results show that the average SSD decrease attributed to light rainfall is 15.2m (14%), moderate rainfall 18.3m (16.8%), and heavy rainfall 21.2m (19.2%). Conclusion: Based on the results and findings, it is correct to conclude that the effect of night rainfall on dark roadways stopping sight distance is somewhat aberrant. It is also correct to suggest that night rainfall on dark roadways will cause a decrease in perception distance travel delay, an increase in braking distance and stopping sight distance.

Study on 3D Terrain Generation and Lightweighting Method of Highway

BIM technology is widely used in highway engineering projects. During the transformation of 2D design and application to 3D, especially for special strip projects such as highways, 3D terrain has problems such as large loading efficiency and low efficiency. Based on the Beijing-Shanghai Highway reconstruction and expansion project, this paper studies the three-dimensional terrain generation and lightweight conversion methods of highway. The terrain construction method is optimized during the formation phase of the terrain, and the polygon is triangulated using the triangular surface growth algorithm. By generating the PHM (Polyhedral Mesh) terrain surface, a three-dimensional terrain model with no deviation, small volume and high generation efficiency is realized. The lightweight 3D terrain model generated by the modeling software can further simplify the 3D terrain and realize the pyramid terrain model with different loading accuracy with different sight distance through grid conversion and tin buffer generation. At the same time, the terrain is projected on satellite images, and The surrounding scenes are deeply fused. The results show that the lightening of terrain in the modeling stage is conducive to improving the modeling efficiency, eliminating the problems of large volume and stuttering of conventional terrain models, and improving the efficiency of terrain export. In the application phase, format conversion and pyramid loading are performed on the terrain, and the lightweight loading of the terrain model is truly realized. The terrain model is seamlessly integrated with the BIM road and other models, and at the same time, it covers elements such as satellite films, enabling real-time browsing based on the B / S (Brower/Server).

Avoiding collision in automated driving situation

Automated driving (AD) is likely to encounter situations, when vehicle control is handed from the system to the human driver. Such situation may occur, e.g., when a steadfast obstacle is suddenly detected in front of the moving vehicle, and emergency breaking is the only way to avoid collision. Probabilistic analytical modeling (PAM) is applied in this analysis to model the vehicle’s and the system’s performance for the given available sight distance (ASD) viewed as a non-random variable and with consideration of the driver’s human capacity factor (HCF). The general concepts are illustrated by numerical examples.

Research on drivers’ visual characteristics in different curvatures and turning conditions of the extra-long urban underwater tunnels

In order to study driver’s visual characteristics under different curvatures and turning conditions in extra-long urban underwater tunnels, fixation and saccade were herein regarded as the main research objectives. In this study, we carried out real vehicle testing on curved sections with 5 different radii and straight sections of the extra-long urban underwater tunnels. The driver’s fixation characteristics were studied by using fixation distribution, fixation time, fixation frequency, fixation time ratio, and frequency ratio. The driver’s saccade characteristics were investigated by selecting the saccade angle, saccade time, saccade frequency, saccade time ratio, and frequency ratio. Accordingly, mathematical models of the driver’s fixation time, fixation frequency, saccade time, and saccade frequency under different curvatures and turning conditions in the extra-long urban underwater tunnel were established. Combined with the change of visual distance, sight distance, and sight zone, driver’s visual characteristics in the extra-long urban underwater tunnel were further analyzed. The results demonstrated that the smaller the radius of the tunnel, the more focused driver’s fixation time, the greater the psychological pressure, and the lower the safety when driving. Under the same radius, driver’s tension and risk factors were higher during turning left, while driver’s driving mentality was more relaxed and driving situation was further stable in the right-turn.

Model of Driver’s Eye Movement and ECG Index under Tunnel Environment Based on Spatiotemporal Data

In order to improve the driver’s physiological and psychological state, the driver’s mental load which is caused by sight distance, lighting, and other factors in the tunnel environment should be quantified via modeling the spatiotemporal data. The experimental schemes have been scientifically designed based on methods of traffic engineering and human factor engineering, which aims to test the driver’s spatiotemporal data of eye movement and ECG (electrocardiogram) index in the tunnel environment. Firstly, the changes in the driver’s spatiotemporal data are analyzed to judge the changing trend of the driver’s workload in the tunnel environment. The results show that the cubic spline interpolation function model can fit the dynamic changes of average pupil diameter and heart rate (HR) growth rate well, and the goodness of fit for the model group is above 0.95. So, tunnel environment makes the driver’s typical physiological indicators fluctuate in the coordinates of time and space, which can be modeled and quantified. Secondly, in order to analyze the classification of tunnel risk level, a fusion model has been built based on the functions of average pupil diameter and HR growth rate. The tunnel environmental risk level has been divided into four levels via the fusion model, which can provide a guidance for the classification of tunnel risk level. Furthermore, the fusion model allows tunnel design and construction personnel to adopt different safety design measures for different risk levels, and this method can effectively improve the economy of tunnel operating safety design.

Modelling risk factors for fatal pedestrian crashes in Kolkata, India

In developing countries, pedestrian safety is an issue of major concern. Although an extensive body of literature is available on the identification of elements related to the pedestrian’s risk; the studies are primarily conducted in urban areas of developed countries. The findings from these studies may only be partially relevant to the cities of an emerging country such as India. The present study analyzes historical crash records obtained from the “Kolkata Police” and identifies the risk factors at the road network level for the hazardous corridors posing a high risk to the pedestrians. The study findings reveal that pedestrians’ fatalities at intersections are associated with a high vehicular volume, higher pedestrian-vehicular interaction, high approach speed, overtaking tendency of vehicles, certain land-use type, encroachment of footpath, inadequate sight distance, inaccessible pedestrian crosswalk, wider minor carriageway, the absence of a pedestrian signal head, and lack of enforcement. On the other hand, the models outcomes reveal that pedestrians’ fatalities at midblock road segments are associated with low pedestrian volume, high approach speed, overtaking tendency of the vehicle, encroachment of footpath, on-street parking, wider road width, certain land-use type, inadequate sight distance, insufficient lighting, and inadequate pavement markings.

Study of Indoor Radio Coverage Performance of Dual Technology Co-Existing MIMO Antenna Platform for Low Power Wireless Base Station

In this paper, we present the radiated mode indoor radio coverage performance study of a co-existing dual technology, dual 4×4 Multiple Input Multiple Output (MIMO) antenna platform. The antenna platform is targeted to be used for low power wireless radio Base Station (BS) applications. One of the 4×4 MIMO antenna pairs operates in the 2.5–2.7 GHz licensed Long Term Evolution (LTE) band while the other MIMO antenna pair operates in the 2.4 GHz unlicensed Wireless Fidelity (Wi-Fi) Industrial Scientific Medical (ISM) band. This radio performance study is carried out to analyze, predict and verify the impact of multi-radio co-existence on the radiated mode indoor coverage performance in an Over-The-Air (OTA) scenario. The study involves OTA radio propagation modeling, prediction and verification both for a near field and far field scenario. While the near field coverage is studied in a small form factor controlled shield box environment, the far field coverage study is undertaken over a 780 ft2 indoor enterprise coverage area. The test result shows the worst case LTE signal level is –77.7, –75, and –76.03 dBm, respectively, over a 3.6 m obstructed radial Line Of Sight (LOS) distance.

Analysis of the factors influencing overtaking in two-lane highways: A driving simulator study

BackgroundHuman factors are among the leading causes of frontal collision accidents. Therefore, understanding the factors that affect driver behaviour during overtaking is essential. ObjectiveThis research proposed a methodology to observe passing manoeuvres on two-lane highways in a driving simulator and to investigate the effects of the speed of an impeding vehicle, the type of the vehicle to be overtaken and the passing sight distance on the following gap distance as an indicator of driver behaviour. MethodThe repeated measures experiment allowed for 640 possible overtakings with a sample of 80 participants. The speed of the impeding vehicle, the type of the impeding vehicle and the passing sight distance were used as within-subject factors with eight treatments. The driver’s age, gender, and experience were considered the between-subject factors. ResultsWhen the speed of the impeding vehicle was 60 km/h, the participants adopted a following gap in passing sight distance of 446 m (M = 81.32 m), which was larger than the following gap in passing sight distance of 560 m (M = 70.84 m). ConclusionAmong the factors that were considered, the effect of the speed of an impeding vehicle on the following gap at the beginning of overtaking was higher than the effect of the type of the impeding vehicle or the passing sight distance. Together, these combination values can describe the driver behaviour and help to improve the standards-based design values to increase safety.

A comprehensive study on factors influencing pedestrian signal violation behaviour: Experience from Kolkata City, India

Signalized intersections with marked crosswalks enhance pedestrian safety by providing the designated right of way to pedestrians. However, a significant number of pedestrian crashes occur at signalized intersections, which may predominantly be due to pedestrians’ violation behaviors. Therefore, it is worthwhile to examine how pedestrian risk and signal violation are associated. For this purpose, pedestrians’ crossing behavior, and perception data have been collected from 55 signalized junctions in Kolkata, India, and a mathematical relationship is developed between the share of pedestrian signal violation and the frequency of fatal pedestrian crashes. The model outcome indicates that there is a significant and positive association between these two variables. Subsequently, with the help of “beta regression model” it is identified that absence of pavement marking, traffic cycle length, inadequate sight distance, on-street parking, a high share of pedestrian carrying overhead loads, pedestrian’s intended mode of transport after crossing, and pedestrian’s sociodemographic characteristics significantly influence the share of pedestrian signal violation behavior. The study finding indicates that while improvement in the design of the built environment and signal settings to increase pedestrians’ convenience and confidence are must, and there is a crucial need to integrate innovative safety management practices to address spatial and temporal needs of an intersection. For example, intersections with high commercial activities generating a high volume of pedestrian carrying overhead goods demand particular pedestrian phase with countdown signals. Further, to control pedestrians’ unruly behavior, adequate pavement marking, zebra crossing, designated bus stop facility, pedestrian signal head, and off-street parking facility should be provided along with the strict enforcement. Moreover, to enhance compliance with traffic signals, road safety campaigns, education, and awareness programs are must for better and safer road use.