Journal articles: 'Available sight distance'

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Wood, Jonathan S., and Eric T. Donnell. "Stopping Sight Distance and Available Sight Distance: New Model and Reliability Analysis Comparison." Transportation Research Record: Journal of the Transportation Research Board 2638, no. 1 (January 2017): 1–9. http://dx.doi.org/10.3141/2638-01.

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Stopping sight distance (SSD) is an important design criterion used in the geometry of highways and streets. Design guidance implies that SSD is used to ensure safety along the roadway. This paper reviews SSD design criteria and develops an updated model to improve consistency between available sight distance and SSD criteria found in geometric design policy. A new variable, the distance from the front of the car to the driver’s eye ( Lfront-eye), is used in the updated model. Distributional values for Lfront-eye are determined. A method accounting for lighted (daytime and lighted nighttime) versus unlighted nighttime conditions is also discussed. A probabilistic analysis of vertical curve SSD uses Monte Carlo simulation. The results of this analysis are compared with the SSD model found in current geometric design policy. Possible values for Lfront-eye that can be used in design guidance are proposed. Potential issues that should be investigated in future work are discussed.

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Easa, Said M., Yasser Hassan, and A. O. Abd El Halim. "Sight distance evaluation on complex highway vertical alignments." Canadian Journal of Civil Engineering 23, no. 3 (June 1, 1996): 577–86. http://dx.doi.org/10.1139/l96-866.

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Sight distance (stopping, passing, and decision) is a key element in highway geometric design. Existing models for evaluating sight distance on vertical alignments are applicable only to simple, isolated elements such as a crest vertical curve, a sag vertical curve, and a reverse vertical curve (a sag curve following a crest curve, or vice versa). This paper presents an analytical methodology for evaluating sight distance on complex vertical alignments that involve any combination of vertical alignment elements. The methodology can be used for evaluating passing sight distance on two-lane highways, and stopping sight distance and decision sight distance on all highways. Sight distance controlled by the headlight beam can also be evaluated. The locations of sight-hidden dips, which may develop when a sag vertical curve follows a crest vertical curve with or without a common tangent, can be determined. Also, sight distances obstructed by overpasses are evaluated. A profile of the available sight distance can be established and used to evaluate sight distance deficiency and the effect of alignment improvements. A software was developed and can be used for determining the available sight distance accurately. The software may replace the current field and graphical practice for establishing the no-passing zones and evaluating stopping and decision sight distances on complex vertical alignments. Key words: sight distance, vertical alignment, highway, passing zones.

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Zeidan, George R., and Patrick T. McCoy. "Effects of Right-Turn Lanes on Driveway Sight Distance." Transportation Research Record: Journal of the Transportation Research Board 1737, no. 1 (January 2000): 78–83. http://dx.doi.org/10.3141/1737-10.

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Vehicles entering a driveway from an exclusive right-turn lane may restrict the sight distance available to vehicles waiting to enter the arterial street from the driveway. The sight distance available to the vehicles waiting at a driveway is a function of the geometric design of the driveway and the right-turn lane. The relationship between available sight distance and the relevant geometric design variables is examined. The analysis identifies geometries that provide adequate sight distances for various design speeds.

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Gargoum, Suliman A., Mostafa H. Tawfeek, Karim El-Basyouny, and James C. Koch. "Available sight distance on existing highways: Meeting stopping sight distance requirements of an aging population." Accident Analysis & Prevention 112 (March 2018): 56–68. http://dx.doi.org/10.1016/j.aap.2018.01.001.

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Ismail, K., and T. Sayed. "New Algorithm for Calculating 3D Available Sight Distance." Journal of Transportation Engineering 133, no. 10 (October 2007): 572–81. http://dx.doi.org/10.1061/(asce)0733-947x(2007)133:10(572).

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Byrd, Patrick S., Patrick T. McCoy, Geza Pesti, and Virendra A. Singh. "Implementation of Wider Lane Lines to Improve Sight Distance from Opposing Left-Turn Lanes." Transportation Research Record: Journal of the Transportation Research Board 1708, no. 1 (January 2000): 12–19. http://dx.doi.org/10.3141/1708-02.

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Vehicles turning left at intersections from opposing left-turn lanes often restrict each other’s sight distance. Previous research has developed guidelines for offsetting opposing left-turn lanes to provide adequate sight distances. Implementation of these guidelines at existing intersections typically involves reconstructing the left-turn lanes. However, the results of the before-and-after studies presented demonstrate that increasing the width of the lane lines between left-turn lanes and the adjacent through lanes also can be used as a means of improving the sight distance between opposing left-turn lanes. Regression analysis was used to determine a relationship between lane-line width and available sight distance that can be used to design lane-line widths that provide the required sight distance for opposing left-turn vehicles.

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Zhang, Chi, Shao Wei Yang, and Min Zhang. "Calculating Method and Safety Evaluation of Highway 3D Available Sight Distance." Applied Mechanics and Materials 97-98 (September 2011): 185–91. http://dx.doi.org/10.4028/www.scientific.net/amm.97-98.185.

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Visual information is the basis of highway traffic safety, which is important for a driver to take right actions in driving. From the driving theory and the driver’s sight characteristics, the concept of available sight distance is put forward. According to extend and apply the theory of the spatial intervisibility between two spots, the math model of calculating and analyzing the spatial available sight distance is built up, which is solved by use of parameter equations and space conversion. On the basis of this model, the safety evaluation model and the evaluation procedures are given. At last, the effectiveness of the model is tested in practical engineering applications, and it can provide the basis for highway geometric design and safety evaluation.

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Sarhan, Mohamed, and Yasser Hassan. "Three-Dimensional, Probabilistic Highway Design." Transportation Research Record: Journal of the Transportation Research Board 2060, no. 1 (January 2008): 10–18. http://dx.doi.org/10.3141/2060-02.

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The potential usefulness of reliability analysis has recently been stressed in many engineering applications. Given the variability in the design parameters, a reliability-based probabilistic approach is well suited to replace the current deterministic highway design practice. However, progress in this regard is generally slow. In this study, the reliability analysis was used to estimate the probability of hazard (POH) that might result from insufficiency of sight distances. As an application, the available sight distance was checked against required stopping sight distance on an assumed road segment. Variation of the design parameters was addressed with Monte Carlo simulation using 100,000 sets of design parameters based on distributions available in the literature. A computer program was developed to use these sets of design parameters to calculate the profiles of available and required stopping sight distances in two- and three-dimensional projections as well as the profile of POH. The approach was applied to a horizontal curve overlapping with flat grade, crest curves, and sag curves in a cut section where the side slope would restrict the sightline. The analysis showed that the current deterministic approach yields very conservative estimates of available and required stopping sight distance, resulting in very low POH. The application example also showed the change of POH with the change of vertical alignment parameters.

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Hassan, Yasser, Said M. Easa, and A. O. Abd El Halim. "Analytical Model for Sight Distance Analysis on Three-Dimensional Highway Alignments." Transportation Research Record: Journal of the Transportation Research Board 1523, no. 1 (January 1996): 1–10. http://dx.doi.org/10.1177/0361198196152300101.

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Existing sight distance models are applicable only to two-dimensional (2-D) separate horizontal and vertical alignments or simple elements of these separate alignments (vertical curve, horizontal curve). A new model is presented for determining the available sight distance on 3-D combined horizontal and vertical alignments. The model is based on the curved parametric elements that have been used in the finite element method. The elements presented are rectangular (4-node, 6-node, and 8-node elements) and triangular. These elements are used to represent various features of the highway surface and sight obstructions, including tangents (grades), horizontal curves, vertical curves, traveled lanes, shoulders, side slopes, cross slopes, superelevation, lateral obstructions, and overpasses. The available sight distance is found analytically by examining the intersection between the sight line and the elements representing the highway surface and the sight obstructions. Application of the new model is illustrated using numerical examples, and the results show that existing 2-D models may underestimate or overestimate the available sight distance. The proposed model should be valuable in establishing design standards and guidelines for 3-D highway alignments and determining the effect of various highway features on sight distance.

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Hassan, Yasser, Said M. Easa, and A. O. Abd El Halim. "Highway Alignment: Three-Dimensional Problem and Three-Dimensional Solution." Transportation Research Record: Journal of the Transportation Research Board 1612, no. 1 (January 1998): 17–25. http://dx.doi.org/10.3141/1612-03.

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Highway geometric design has usually been considered in separate two-dimensional (2-D) projections of horizontal and vertical alignments. Such a practice was followed mainly because three-dimensional (3-D) analysis of combined highway alignments was expected to be difficult. As a result, the effect of ignoring the 3-D nature of the highway alignment could not be quantified. With the long-term objective of developing 3-D design practice, a framework for 3-D highway geometric design was developed and 3-D sight distance was extensively studied as the first design basis. The status of sight distance in current design policies and previous research is summarized, and mainly 2-D analysis was considered. The five main tasks performed to cover the 3-D highway sight distance are presented. ( a) As a preliminary step, the 2-D sight distance on complex separate horizontal and vertical alignments was modeled, and the finite element method was used for the first time in the highway geometric design. ( b) The 2-D models were then expanded to cover the daytime and nighttime sight distances on 3-D combined alignments. ( c) The analytical models were coded into computer software that can determine the available sight distance on actual highway segments. ( d) The models were applied in 3-D design of combined horizontal and vertical curves in cut-and-fill sections, and preliminary design aids were derived. ( e) Finally, a new concept of red zones was suggested to mark the locations on alignments designed according to current practices where the available sight distance will drop below that required. A comprehensive work on 3-D sight distance analysis has been compiled that should be of great importance for highway researchers and professionals.

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Son, Young-Tae, Sang-Gu Kim, and Jin-Kak Lee. "Methodology to Calculate Sight Distance Available to Drivers at Skewed Intersections." Transportation Research Record: Journal of the Transportation Research Board 1796, no. 1 (January 2002): 41–47. http://dx.doi.org/10.3141/1796-05.

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Lee, Soo-Beom, and William D. Berg. "Development of Safety-Based Level-of-Service Parameters for Two-Way Stop-Controlled Intersections." Transportation Research Record: Journal of the Transportation Research Board 1635, no. 1 (January 1998): 127–32. http://dx.doi.org/10.3141/1635-17.

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Current methods for evaluating level of service at two-way stop-controlled intersections do not account for safety considerations. One of the most important factors influencing intersection safety is the availability of adequate sight distance. However, current recommended intersection sight distance criteria do not explicitly consider variability in traffic composition, vehicle characteristics, pavement conditions, or driver characteristics such as perception-reaction time and minimum gap acceptance. Research was therefore undertaken to develop and validate a method where the safety of a two-way stop-controlled intersection could be estimated based on parameters such as intersection geometry, traffic volume, pavement condition, traffic composition, and available sight distances. Simulation modeling was used to estimate the frequency of potential conflicts or collisions resulting from sight distance restrictions. The potential severity of the collisions was modeled using kinetic energy principles. A method for incorporating the results into a level-of-service evaluation framework was then developed.

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Hassan, Yasser. "Improved Design of Vertical Curves with Sight Distance Profiles." Transportation Research Record: Journal of the Transportation Research Board 1851, no. 1 (January 2003): 13–24. http://dx.doi.org/10.3141/1851-02.

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Design of vertical alignment is one of the main tasks in highway geometric design. This task requires, among other things, that the designer ensure drivers always have a clear view of the road so they can stop before hitting an unexpected object in the road. Therefore, the ability to determine the required and available stopping sight distance (SSD) at any point of the vertical alignment is essential for the design process. Current design guides in the United States and Canada provide simple analytical models for determining the minimum length of a vertical curve that would satisfy the sight distance requirement. However, these models ignore the effect of grade on the required SSD. Alternative approaches and models have also been suggested but cover only special cases of vertical curves. Two specific models were expanded to determine the required SSD on crest and sag vertical curves. By comparing profiles of available SSD and required SSD on examples of vertical curves, it was shown that current North American design practices might yield segments of the vertical curve where the driver’s view is constrained to a distance shorter than the required SSD. An alternative design procedure based on the models was developed and used to determine the minimum lengths of crest and sag vertical curves. Depending on the approach grade, these new values of minimum curve length might be greater than or less than values obtained through conventional design procedures. Design aids were therefore provided in tabular form for designers’ easy and quick use.

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Bassani, M., N. Grasso, and M. Piras. "3D GIS BASED EVALUATION OF THE AVAILABLE SIGHT DISTANCE TO ASSESS SAFETY OF URBAN ROADS." ISPRS - International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences XL-3/W3 (August 19, 2015): 137–43. http://dx.doi.org/10.5194/isprsarchives-xl-3-w3-137-2015.

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The available sight distance (ASD) in front of the driver to detect possible conflicts with unexpected obstacles is fundamental for traffic safety. In the last 20 years, road design software (RDS) has been continuously updated with dedicated modules to estimate ASD, thus assessing the quality of project from a safety point of view. Unfortunately, the evaluation of ASD still represents an issue in the case of existing road, and the object of discussion in the research community. To avoid problems related to the limitation associated with the use of digital terrain models typically employed in RDS, the Geographic Information Systems (GIS) software can use digital surface models (DSM) which are more flexible in the modelling of sight obstruction due to vegetation, street furniture, and vertical surfaces largely diffused in urbanized areas. <br><br> The paper deals with the evaluation of GIS in the estimation of ASD in a typical urban road where the density of sight obstruction along the roadside is relatively high. The work explores the case study of a collector road in the city of Turin (Italy). Results confirm the potentiality of GIS software in capturing the complex morphology of the urban environment, thus confirming that GIS could become an important analysis tool for road engineers in the field of road safety. The investigation here described is part of the Pro-VISION Project (funded in 2014 by the <i>Regione Piemonte</i>, Italy).

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de Santos-Berbel, César, Mohamed Essa, Tarek Sayed, and María Castro. "Reliability-Based Analysis of Sight Distance Modelling for Traffic Safety." Journal of Advanced Transportation 2017 (2017): 1–12. http://dx.doi.org/10.1155/2017/5612849.

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Sight distance is of the utmost importance for traffic safety. The consideration of three-dimensional (3D) available sight distance (ASD) in geometric design has been supported by several researchers. However, existing ASD estimation methods are two-dimensional (2D) in nature, which do not evaluate varying visibility conditions. This paper compares different methodologies of modelling the ASD. The ASD of 402 horizontal curves, located in twelve in-service two-lane rural highways, was analyzed. Three ASD estimation methods were used which include a 2D method and two different 3D methods. The ASD results obtained through 2D and 3D methodologies are compared. Also, the different conditions of the existing roadside features or geometric elements, under which the 3D ASD estimation is important, were identified. Next, reliability theory is utilized to evaluate the risk level (probability of noncompliance,Pnc) associated with limited sight distance for each ASD modelling method. The results of the comparison emphasized the importance of considering the 3D modelled sight distance when evaluating the associated risk either in highway design or during the service life. In addition, the results indicated that the ASD modelling approach can have a significant impact on the estimation of the safety of highway design.

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Hassan, Yasser, and Said M. Easa. "Sight distance red zones on combined horizontal and sag vertical curves." Canadian Journal of Civil Engineering 25, no. 4 (August 1, 1998): 621–30. http://dx.doi.org/10.1139/l97-127.

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Coordination of highway horizontal and vertical alignments is based on subjective guidelines in current standards. This paper presents a quantitative analysis of coordinating horizontal and sag vertical curves that are designed using two-dimensional standards. The locations where a horizontal curve should not be positioned relative to a sag vertical curve (called red zones) are identified. In the red zone, the available sight distance (computed using three-dimensional models) is less than the required sight distance. Two types of red zones, based on stopping sight distance (SSD) and preview sight distance (PVSD), are examined. The SSD red zone corresponds to the locations where an overlap between a horizontal curve and a sag vertical curve should be avoided because the three-dimensional sight distance will be less than the required SSD. The PVSD red zone corresponds to the locations where a horizontal curve should not start because drivers will not be able to perceive it and safely react to it. The SSD red zones exist for practical highway alignment parameters, and therefore designers should check the alignments for potential SSD red zones. The range of SSD red zones was found to depend on the different alignment parameters, especially the superelevation rate. On the other hand, the results showed that the PVSD red zones exist only for large values of the required PVSD, and therefore this type of red zones is not critical. This paper should be of particular interest to the highway designers and professionals concerned with highway safety.Key words: sight distance, red zone, combined alignment.

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Hassan, Yasser, Said M. Easa, and A. O. Abd El Halim. "State-of-the-art of three-dimensional highway geometric design." Canadian Journal of Civil Engineering 25, no. 3 (June 1, 1998): 500–511. http://dx.doi.org/10.1139/l97-111.

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Geometric design is an important phase in the highway design process that is directly related to traffic safety. Highway elements should be jointly designed to account for such design criteria as sight distance, vehicle stability, driver comfort, drainage, and aesthetics. Intuitively, such a design should be based on a three-dimensional (3-D) analysis. This paper reviews the current practice and research work related to each design criterion with emphasis on the conformity with the 3-D nature of the highway. Current standards are based mainly on a two-dimensional (2-D) analysis that does not guarantee a satisfactory design. Recently, several research efforts have been expended in the 3-D highway analysis with sight distance being the most researched area. Analytical models and computer software have been developed to accurately model 3-D daytime and nighttime sight distances. Roads designed using current 2-D standards may compromise safety or economy. Different models are currently available to simulate the forces acting on a vehicle in 3-D. These models show that the point-mass formula for modelling vehicle dynamics in the current standards can be inaccurate. Current standards contain recommendations for drainage of surface water, but explicit quantitative coordination of combined alignments is lacking. Furthermore, research is still needed to study the effect of alignment coordination on highway aesthetics and driver's perception of information.Key words: highway geometric design, three-dimensional analysis, sight distance, vehicle dynamics, drainage, highway aesthetics.

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Bhattacharya, Jishnu. "Numerical evaluation of time-distance helioseismic sensitivity kernels in spherical geometry." Astronomy & Astrophysics 659 (March 2022): A138. http://dx.doi.org/10.1051/0004-6361/202141665.

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Context. Helioseismic analysis of large-scale flows and structural inhomogeneities in the Sun requires the computation of sensitivity kernels that account for the spherical geometry of the Sun, as well as systematic effects such as line-of-sight projection. Aims. I aim to develop a code to evaluate helioseismic sensitivity kernels for flows using line-of-sight projected measurements. Methods. I decomposed the velocity field in a basis of vector spherical harmonics and computed the kernel components corresponding to the coefficients of velocity in this basis. The kernels thus computed are radial functions that set up a 1.5D inverse problem to infer the flow from surface measurements. I demonstrate that using the angular momentum addition formalism lets us express the angular dependence of the kernels as bipolar spherical harmonics, which may be evaluated accurately and efficiently. Results. Kernels for line-of-sight projected measurements may differ significantly from those that don’t account for projection. Including projection in our analysis does not increase the computational time significantly. We demonstrate that it is possible to evaluate kernels for pairs of points that are related through a rotation by linearly transforming the terms that enter the expression of the kernel, and that this result holds even for line-of-sight projected kernels. Conclusions. I developed a Julia code that may be used to evaluate sensitivity kernels for seismic wave travel times computed using line-of-sight projected measurements, which is made freely available under the MIT license.

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Bassani, Marco, Nives Grasso, Marco Piras, and Lorenzo Catani. "Estimating the Available Sight Distance in the Urban Environment by GIS and Numerical Computing Codes." ISPRS International Journal of Geo-Information 8, no. 2 (January 30, 2019): 69. http://dx.doi.org/10.3390/ijgi8020069.

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The available sight distance (ASD) is that part of the roadway ahead which is visible to the driver, and should be of sufficient length to allow a vehicle traveling at the designated speed to stop before reaching a stationary object in its path. It is fundamental in assessing road safety of a project or on an existing road section. Unfortunately, an accurate estimation of the available sight distance is still an issue on existing roads, above all due to the lack of information regarding the as-built condition of the infrastructure. Today, the geomatics field already offers different solutions for collecting 3D information about environments at different scales, integrating multiple sensors, but the main issue regarding existing mobile mapping systems (MMSs) is their high cost. The first part of this research focused on the use of a low-cost MMS as an alternative for obtaining 3D information about infrastructure. The obtained model can be exploited as input data of specific algorithms, both on a GIS platform and in a numerical computing environment to estimate ASD on a typical urban road. The aim of the investigation was to compare the performances of the two approaches used to evaluate the ASD, capturing the complex morphology of the urban environment.

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Gavran, Dejan, Sanja Fric, Vladan Ilić, and Filip Trpčevski. "SIGHT DISTANCE ANALYSES IN ROAD DESIGN PROCESS: SERBIAN PRACTICE." TRANSPORT 31, no. 2 (June 28, 2016): 250–59. http://dx.doi.org/10.3846/16484142.2016.1193052.

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New Serbian policies on road design introduce the concept of operating speeds. Decades ago, national policies were based on the constant design speed concept. Among other design parameters, in relation to that constant design speed, minimum radii of horizontal and vertical road geometry were determined. Introduction of the operating speed concept provides for more realistic prediction of speed levels along the road. Unlike the constant design speed, operating speed levels vary along the road, reaching higher levels in curves with larger radii, on straight sections and on reverse curves and dropping down to the design speed level in horizontal curves with the minimum radius. Consequently, besides a constant Stopping Sight Distance (SSD), which is calculated from the constant design speed, the new term, Required Sight Distance (RSD) is introduced. RSD varies along the road, as it is calculated from the operating speed, which also varies along the road. Appropriate RSD analyses are crucial on road rehabilitation projects, since a simple resurfacing that enables higher speed levels, without providing increased RSD, may hamper the safety of a newly resurfaced road. Software tools for predicting operating speed levels and optical analyses of the road are also presented in this paper. Software tools for RSD analyses enable the import of lines of sight into the 3D model of the roadway and their export into the cross sections extracted from the model, thus facilitating the obstacle removal. Also demonstrated are tools for determining Available Sight Distance (ASD), which are based on triangulated 3D models of the roadway as well.

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Zhang, Yue. "The Stopping Sight Distance Test for Freeway Based on the Operating Speed." Applied Mechanics and Materials 97-98 (September 2011): 180–84. http://dx.doi.org/10.4028/www.scientific.net/amm.97-98.180.

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In this paper, the stopping sight distance of passenger car based on the operating speed was regarded as guideposts, and its corresponding radius of horizontal curve and vertical curve was got according to the calculated results, and available for reference and application in the alignment design and safety evaluation for freeway.

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Moreno, Ana Tsui, Vicente Ferrer, and Alfredo Garcia. "Evaluation of 3D coordination to maximize available stopping sight distance in two-lane rural highways." Baltic Journal of Road and Bridge Engineering 9, no. 2 (June 20, 2014): 94–100. http://dx.doi.org/10.3846/bjrbe.2014.12.

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Shalkamy, Amr, Karim El-Basyouny, and Hai Yang Xu. "Voxel-Based Methodology for Automated 3D Sight Distance Assessment on Highways using Mobile Light Detection and Ranging Data." Transportation Research Record: Journal of the Transportation Research Board 2674, no. 5 (May 2020): 587–99. http://dx.doi.org/10.1177/0361198120917376.

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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.

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Kilani, Omar, Maged Gouda, Jonas Weiß, and Karim El-Basyouny. "Safety Assessment of Urban Intersection Sight Distance Using Mobile LiDAR Data." Sustainability 13, no. 16 (August 18, 2021): 9259. http://dx.doi.org/10.3390/su13169259.

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This paper proposes an automated framework that utilizes Light Detection and Ranging (LiDAR) point cloud data to map and detect road obstacles that impact drivers’ field of view at urban intersections. The framework facilitates the simulation of a driver’s field of vision to estimate the blockage percentage as they approach an intersection. Furthermore, a collision analysis is conducted to examine the relationship between poor visibility and safety. The visibility assessment was used to determine the blockage percentage as a function of intersection control type. The safety assessment indicated that intersections with limited available sight distances (ASD) exhibited an increased risk of collisions. The research also conducted a sensitivity analysis to understand the impact of the voxel size on the extraction of intersection obstacles from LiDAR datasets. The findings from this research can be used to assess the intersection without the burden of manual intervention. This would effectively support transportation agencies in identifying hazardous intersections with poor visibility and adopt policies to enhance urban intersections’ operation and safety.

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Himes, Scott, Richard J. Porter, and Kimberly Eccles. "Safety Evaluation of Geometric Design Criteria: Intersection Sight Distance at Unsignalized Intersections." Transportation Research Record: Journal of the Transportation Research Board 2672, no. 39 (July 15, 2018): 11–19. http://dx.doi.org/10.1177/0361198118783162.

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A Policy on Geometric Design of Highways and Streets, 6th Edition, (publisher: AASHTO), provides design criteria for minimum sight distances, including intersection sight distance (ISD). An understanding of the relationship between ISD and safety at stop-controlled intersections is needed, with potential applications of this knowledge to both performance-based design and substantive road safety management practices. To establish this relationship, crash, traffic, and geometric data were collected from 832 two-lane minor unsignalized intersection approaches in Ohio, and Washington. The data were analyzed using a cross-sectional study design to quantify the relationship between safety and ISD. The analyses indicated that the expected number of target crashes are associated with available ISD. Target crash frequencies increase as available ISD decreases. Results suggest that ISD is associated with expected crash frequency in a non-linear fashion. The sensitivity of the expected number of target crashes to changes in ISD is highest when ISD is shorter, and decreases as ISD increases (i.e., the safety benefit of increasing ISD from 300 to 600 ft is substantially larger than the safety benefit of increasing ISD from 1,000 to 1,300 ft). The results also suggest that the impacts of ISD on crash frequencies vary as a function of the major road two-way annual average daily traffic and the major road speed limit. The sensitivity of the expected number of crashes to changes in ISD increases as both traffic volume and speed limit increase. Crash modification functions for each of the target crash types were estimated using the regression models.

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Chu, Longjia, and Tien F. Fwa. "Incorporating Braking Distance Evaluation into Pavement Management System for Safe Road Operation." Transportation Research Record: Journal of the Transportation Research Board 2639, no. 1 (January 2017): 119–28. http://dx.doi.org/10.3141/2639-15.

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Maintaining a sufficiently short stopping distance is an important requirement for safe road operation. Stopping sight distances of road sections are decided during the highway alignment and roadway geometric design phase of the road development process. A pavement friction coefficient is used in the calculation of the stopping distances. Since pavement friction coefficient deteriorates with time under traffic action, and the available friction also reduces in wet weather, it is important for pavement maintenance engineers to ensure that sufficient skid resistance is maintained under actual operating conditions so that the stopping distances of road sections are less than the required safe stopping distance. This result requires pavement engineers to monitor regularly the available pavement skid resistance and the corresponding stopping distance of individual road sections. Because skid resistance is an accepted pavement condition to be measured in a pavement management system, it is proposed in this study that braking distance assessment be included as a part of the pavement condition monitoring program of a pavement management system. The proposed procedure consists of two parts: ( a) measurement of skid resistance and evaluation of braking distance and stopping distance and ( b) monitoring of the deterioration trends of individual road sections. The detailed procedure and the analytical tools necessary for the evaluation and prediction of braking and stopping distances, including a finite element skid resistance simulation model, are presented. A numerical example is presented to illustrate the concept and working of the proposed procedure.

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Moreno, Ana Tsui, Alfredo Garcia, Carlos Llorca, and Francisco Javier Camacho-Torregrosa. "Influence of highway three-dimensional coordination on drivers’ perception of horizontal curvature and available sight distance." IET Intelligent Transport Systems 7, no. 2 (June 1, 2013): 244–50. http://dx.doi.org/10.1049/iet-its.2012.0146.

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Cook, Daniel J., Douglas W. Harwood, Ingrid B. Potts, Eric T. Donnell, and Bachir Hamadeh. "Reliability Analysis for Roadway Curves with Horizontal Sightline Obstructions." Transportation Research Record: Journal of the Transportation Research Board 2673, no. 8 (May 2, 2019): 611–22. http://dx.doi.org/10.1177/0361198119845352.

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Objects on the inside of a horizontal curve may limit the stopping sight distance (SSD) available to drivers. Crash analysis shows that SSD-related crashes on horizontal curves are limited in number and difficult to quantify. As an alternative, a reliability analysis model was developed to quantify the number of drivers per year who may encounter a stopped vehicle in a sight-restricted area, creating an opportunity where an SSD-related crash might occur on a roadway with a sight obstruction on the inside of a horizontal curve. The model considers roadway alignment in three dimensions. The model formulation is documented and an analysis of the sensitivity of crash opportunities to traffic volume and offset to a sight obstruction is performed. A sensitivity analysis of the reliability analysis model shows that the percentage of vehicles that may encounter a crash-involved vehicle or a queue of stopped vehicles over the course of a year can range from essentially zero to a value approaching 1% of the total yearly flow. The reliability analysis model is a flexible tool that can be used by planners and designers to compare, in a relative sense, the need for sight distance improvements on specific horizontal curves.

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Scannapieco, Evan, and Crystal L. Martin. "Constraining the Intergalactic Medium Enrichment History with QSO Pairs." Proceedings of the International Astronomical Union 5, S265 (August 2009): 163–66. http://dx.doi.org/10.1017/s1743921310000463.

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AbstractIntergalactic metals are ubiquitous, but their sources remain unknown. A key constraint on these sources is the spatial distributions of metals. Yet, the clustering of metals is difficult to interpret along single lines-of-sight, because distance and velocity information are mixed in redshift space. To overcome this situation we are carrying out detailed comparisons between the line-of-sight and transverse distributions of metal line absorption systems observed in a large sample of QSO pairs and simulations including a wide range of IGM-enrichment scenarios. The degeneracy between distance and velocity is broken by the transverse information available in pairs of sightlines, and thus these comparisons are providing unique new constraints on when and where metals were ejected from galaxies.

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Fambro, Daniel B., Kay Fitzpatrick, and Charles W. Russell. "Operating Speed on Crest Vertical Curves with Limited Stopping Sight Distance." Transportation Research Record: Journal of the Transportation Research Board 1701, no. 1 (January 2000): 25–31. http://dx.doi.org/10.3141/1701-04.

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Horizontal and vertical elements of a highway are designed based on an assumed design speed. This concept was developed in the 1930s as a mechanism for designing rural alignments to permit most drivers to operate uniformly at their desired speed. In 1938, AASHO recognized that drivers select a speed influenced by the roadway environment instead of an assumed design speed. Recent research suggests that design speed is no longer the speed adopted by the faster group of drivers but that it has become a value used to establish the sharpness of horizontal and vertical design elements. The objective of this study was to establish the relationship between design and operating speeds for crest vertical curves with limited sight distance. Geometric data and 3,500 paired speeds (speeds at control and crest sections) were collected at 36 sites in 3 states. The results indicated that both the 85th percentile and the mean operating speeds were well above the inferred design speeds of the crest vertical curves for the range of conditions studied and that the lower the design speed the larger the difference between the 85th percentile speed and the design speed. The mean reductions in speed between the control and crest sections tend to increase as available sight distance is decreased; however, the reduction in speed is less than that suggested by current AASHTO criteria.

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Hazoor, Abrar, Alberto Terrafino, Leandro L. Di Stasi, and Marco Bassani. "How to take speed decisions consistent with the available sight distance using an intelligent speed adaptation system." Accident Analysis & Prevention 174 (September 2022): 106758. http://dx.doi.org/10.1016/j.aap.2022.106758.

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Ma, Yang, Yubing Zheng, Jianchuan Cheng, and Said Easa. "Analysis of dynamic available passing sight distance near right-turn horizontal curves during overtaking using LiDAR data." Canadian Journal of Civil Engineering 47, no. 9 (September 2020): 1059–74. http://dx.doi.org/10.1139/cjce-2019-0138.

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The purpose of this study is twofold: to construct a model for measuring dynamic available passing sight distance (APSD) during overtaking using light detection and ranging (LiDAR) data, and to investigate the effects of several critical variables on dynamic APSD. The analysis considers a single passed vehicle with several variables, including vehicle dimensions Dp, initial headway IH, and speed differential SD. The proposed model simulates the passing process and dynamically estimates APSD considering two types of obstacles: (1) obstacles related to the road environment and (2) passed-vehicle obstacle which is critical especially on or near right-turn horizontal curves. Through multiple tests, the variation of dynamic APSD along with the passing maneuver is established. The results show that large Dp or long IH may increase the adverse effect of the passed vehicle on dynamic APSD. Either too large or too small SD may lead to a relatively high risk of head-on collisions.

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Maaß, Eric, and Frederike D. Hanke. "Distance Estimation in Reproduction Tasks in a Harbor Seal (Phoca vitulina)." Water 13, no. 7 (March 30, 2021): 938. http://dx.doi.org/10.3390/w13070938.

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Harbor seals commute between haul-out places and feeding grounds close to the shore or in the open ocean, which is considered a low structured environment, at first sight not providing many cues for orientation/navigation. Nevertheless, seals are well-oriented. For returning to a specific location, seals may use both external and internal cues to, for example, perform path integration requiring the integration of distances traveled and angles steered. We herein assessed the seal’s ability to estimate distances, previously swum or unknown, in reproduction tasks. Reproduction tasks refer to an experimental paradigm in which the experimental animal is required to swim a specific distance first and subsequently reproduce this distance, with visual cues present or absent. The seal was able to estimate and then reproduce distances (0.5–18.5 m) with the smallest error below 10% of the actual distance, and its precision was higher with distances repeatedly swum compared to its performance with unfamiliar distances. In the absence of visual cues, the seal’s performance slightly dropped; however, it was still able to perform the task with an error of 21%. In conclusion, distance estimation may help seals to navigate precisely towards their goals, even if, for example, visual information is not available.

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González-Gómez, Iglesias, Rodríguez-Solano, and Castro. "Framework for 3D Point Cloud Modelling Aimed at Road Sight Distance Estimations." Remote Sensing 11, no. 23 (November 20, 2019): 2730. http://dx.doi.org/10.3390/rs11232730.

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Existing roads require periodic evaluation in order to ensure safe transportation. Estimations of the available sight distance (ASD) are fundamental to make sure motorists have sufficient visibility to perform basic driving tasks. Mobile LiDAR Systems (MLS) can provide these evaluations with accurate three-dimensional models of the road and surroundings. Similarly, Geographic Information System (GIS) tools have been employed to obtain ASD. Due to the fact that widespread GIS formats used to store digital surface models handle elevation as an attribute of location, the presented methodology has separated the representation of ground and aboveground elements. The road geometry and surrounding ground are stored in digital terrain models (DTM). Correspondingly, abutting vegetation, manmade structures, road assets and other roadside elements are stored in 3D objects and placed on top of the DTM. Both the DTM and 3D objects are accurately obtained from a denoised and classified LiDAR point cloud. Based on the consideration that roadside utilities and most manmade structures are well-defined geometric elements, some visual obstructions are extracted and/or replaced with 3D objects from online warehouses. Different evaluations carried out with this method highlight the tradeoff between the accuracy of the estimations, performance and geometric complexity as well as the benefits of the individual consideration of road assets.

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Sheingold, Brenda Helen, Joyce A. Hahn, and Anne Hofmeyer. "Hiding In Plain Sight: Building Community Social Capital In Distance Education Graduate Programs." Contemporary Issues in Education Research (CIER) 6, no. 2 (March 27, 2013): 265. http://dx.doi.org/10.19030/cier.v6i2.7737.

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There is an increasing global demand for a broad range of academic programs to be offered by distance education. The development of flexible online technology has made studying for a degree anywhere and anytime possible and this option has significant appeal for many people. However, there is limited knowledge available to guide faculty in the strategic development of supportive learning environments for distance education students that fosters connectedness for academic success. The purpose of this three-phase study was to introduce the concept of community social capital to a cohort of graduate nursing students (N=97) and then track implementation and impact in their on-line academic learning environment. Understanding social capital at the onset of graduate school can lead to an improved sense of how students can utilize and grow social capital, enhance bonding, and increase their academic advantage. The findings inform future education curricula, innovative strategies, and educational research agendas by suggesting that social capital awareness is beneficial to students enrolled in distance education.

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Bassani, M., L. Catani, A. Salussolia, and C. Y. D. Yang. "A driving simulation study to examine the impact of available sight distance on driver behavior along rural highways." Accident Analysis & Prevention 131 (October 2019): 200–212. http://dx.doi.org/10.1016/j.aap.2019.07.003.

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Kerber, F., C. Kienel, R. Weinberger, and R. Danner. "Extinction distances: partly new access to an old problem." Symposium - International Astronomical Union 180 (1997): 48. http://dx.doi.org/10.1017/s0074180900129791.

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The distance determination to planetary nebulae (PNe) remains a serious problem as illustrated during the last IAU symposium in 1991 (Terzian, IAU 155, p.109). Since then the situation has not improved significantly. The number of stars for which reddening and spectral data are available, though, has increased tremendously over the last decade. Using data from the literature we have determined extinction distances for more than 50 PNe. The extinction distance method has been pioneered by Lutz (ApJ 181, 135 (1973)) and Acker (A&AS 33, 367 (1978)). The basic assumption of the extinction method is that a reddening vs distance relation (RDR) exists along the line of sight to a given object. Once this relation and the reddening of the object itself is known, a distance to the object can be derived. Gathier et al. (A&A 157, 171 (1986)) present a thorough discussion of the advantages and possible problems of the method. The most recent contributions are by Martin (A&A 281, 526 (1994)) and Saurer (A&A 297, 261 (1995)).

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Sheikholeslami, Sina, Amin M. Boroujerdian, and Morteza Asadamraji. "A Rural Road Accident Probability Model Based on Single-Vehicle Hazard Properties including Hazard Color and Mobility: A Driving Simulator Study." Journal of Advanced Transportation 2020 (November 19, 2020): 1–8. http://dx.doi.org/10.1155/2020/8826374.

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Road safety has recently been considered an important issue in the country. Single-vehicle accident statistics show the importance of this issue. From a safety viewpoint, drivers need to have a reasonable time window for hazard recognition and reaction; therefore, the hazard has to be in sight from a distance preferably longer than the standard minimum stopping sight distance. Nevertheless, if the roadside configuration makes the sight available for a very long distance, the hazard properties are the ones defining the visibility. The hazard size, color, and mobility are some of the most important hazard properties, which may mainly interact with ambient light (like being day or night) and driving speed. In this research, effect of hazard properties on driving accident likelihood was investigated in a condition that enough recognition and reaction time window was available for the driver to provide a ceteris paribus experiment. To fulfil that in a safe experiment condition, a driving simulator was used to test the behavior of 90 licensed drivers encountering an average of 14 hazards with various sets of properties. Based on the findings of this research, there are some interactions between influential hazard properties. The results imply that it is approximately 23% more likely to observe an accident when encountering a dark small stationary hazard at nighttime like a dark-colored with an observed size of 0.5 m × 0.5 m (e.g., a stone) than a major moving light-colored hazard in the daytime like a camel of 1.5 m ∗ 2 m in size. A green-colored hazard is 27% less likely to involve in an accident at nighttime than hazards with other colors. Each 10 km/h speed increment leads to 1.9% more accident likelihood, and every time the driver encounters a hazard, they will be 0.84% less likely to crash next time.

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Jose Andueza, Pedro. "Mathematical Models of Vehicular Speed on Mountain Roads." Transportation Research Record: Journal of the Transportation Research Board 1701, no. 1 (January 2000): 104–10. http://dx.doi.org/10.3141/1701-13.

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Mathematical models were developed to estimate vehicular speed on curves and tangents in mountain roads. The 85th percentile speed for curves was estimated by using the radius of the curve under consideration, the radius of the previous curve, sight distance in the curve, and tangent length before the curve. The average speed was calculated by using the radius of the curve under consideration, the radius of the previous curve, and sight distance. The 85th percentile and the average speed were estimated by using the radius of the previous curve and tangent length. Speeds adopted by drivers respond not to engineer’s design speed but to geometric characteristics of the road. A design procedure is proposed that takes advantage of available design speed and driver behavior on the road at the same time. On a curve, drivers consider two efficiency measures: speed and comfort. On some curves, they prefer to feel a certain degree of discomfort in exchange for obtaining greater speeds. For some geometric conditions, drivers adopt a speed that sacrifices not only comfort but also safety.

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Wang, Ye, Wen-jun Lu, and Hong-bo Zhu. "An Empirical Path-Loss Model for Wireless Channels in Indoor Short-Range Office Environment." International Journal of Antennas and Propagation 2012 (2012): 1–7. http://dx.doi.org/10.1155/2012/636349.

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A novel empirical path-loss model for wireless indoor short-range office environment at 4.3–7.3 GHz band is presented. The model is developed based on the experimental datum sampled in 30 office rooms in both line of sight (LOS) and non-LOS (NLOS) scenarios. The model is characterized as the path loss to distance with a Gaussian random variableXdue to the shadow fading by using linear regression. The path-loss exponentnis fitted by the frequency using power function and modeled as a frequency-dependent Gaussian variable as the standard deviationσofX. The presented works should be available for the research of wireless channel characteristics under universal indoor short-distance environments in the Internet of Things (IOT).

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Gopalan, Kaliappan, Brett Y. Smolenski, and Darren Haddad. "Detection and classification of drones using Fourier-Bessel series representation of acoustic emissions." Journal of the Acoustical Society of America 152, no. 4 (October 2022): A40. http://dx.doi.org/10.1121/10.0015472.

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Detection, classification, and line-of-sight range estimation of drones are vital for security, safety, and privacy reasons. Representation of the audio emissions of drones in a Fourier-Bessel (FB) series expansion is proposed for the identification of a drone and/or the prediction of its range from an observation point. A deep learning network employing the FB series coefficients as the preprocessed input has been shown to classify accurately each of seven drones flying in a controlled environment in about 84 % of cases. For the case of any one of three drones flying outdoors, presence of the drone—as opposed to background noise—was detected correctly with few false positive and false negative results. Additionally, the range of the drone—from 2.5 m to 935.6 m—was estimated to be within ±50 cm of actual line-of-sight distance in over 85 % of the available test cases.

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42

Lioi, A., A. Hazoor, M. Castro, and M. Bassani. "Impact on driver behaviour of guardrails of different height in horizontal-vertical coordinated road scenarios with a limited available sight distance." Transportation Research Part F: Traffic Psychology and Behaviour 84 (January 2022): 287–300. http://dx.doi.org/10.1016/j.trf.2021.12.008.

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Tomic, Slavisa, and Marko Beko. "Target Localization via Integrated and Segregated Ranging Based on RSS and TOA Measurements." Sensors 19, no. 2 (January 9, 2019): 230. http://dx.doi.org/10.3390/s19020230.

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This work addresses the problem of target localization in adverse non-line-of-sight (NLOS) environments by using received signal strength (RSS) and time of arrival (TOA) measurements. It is inspired by a recently published work in which authors discuss about a critical distance below and above which employing combined RSS-TOA measurements is inferior to employing RSS-only and TOA-only measurements, respectively. Here, we revise state-of-the-art estimators for the considered target localization problem and study their performance against their counterparts that employ each individual measurement exclusively. It is shown that the hybrid approach is not the best one by default. Thus, we propose a simple heuristic approach to choose the best measurement for each link, and we show that it can enhance the performance of an estimator. The new approach implicitly relies on the concept of the critical distance, but does not assume certain link parameters as given. Our simulations corroborate with findings available in the literature for line-of-sight (LOS) to a certain extent, but they indicate that more work is required for NLOS environments. Moreover, they show that the heuristic approach works well, matching or even improving the performance of the best fixed choice in all considered scenarios.

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Ratnatunga, Kavan U. "The Similarity of the Halo Field K Giant Population by the Globular Cluster System of our Galaxy." Symposium - International Astronomical Union 126 (1988): 519–20. http://dx.doi.org/10.1017/s007418090004290x.

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Line-of-sight velocities and improved metal abundance estimates are available for a representative sample of 58 giants located by an objective prism survey (Ratnatunga and Freeman 1985), in a 20 square degree field near SA 127 (1 = 272, b = +39). These in-situ K-giants of the outer regions of our galactic halo give a direct comparison of the field population with the globular cluster system. Fig. 1 illustrates the distribution of line-of-sight velocity with abundance for the sample of giant stars in SA 127. The mean and dispersion of the sample appears to be discontinuous at [FeH] ~ −0.8. Fig. 2 shows the distribution of [Fe/H] with distance from the Sun for the same stars. The metal stronger giants (filled symbols) represent a population of stars up to 6 kpc above the plane of the disk and have a velocity dispersion of about 50 km/s. In contrast, the metal weaker giants have a typical halo dispersion of about 120 km/s.

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Amjad, Kashif, Muhammad Ali, Sohail Jabbar, Majid Hussain, Seungmin Rho, and Mucheol Kim. "Impact of Dynamic Path Loss Models in an Urban Obstacle Aware Ad Hoc Network Environment." Journal of Sensors 2015 (2015): 1–8. http://dx.doi.org/10.1155/2015/286270.

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This study highlights the importance of the physical layer and its impact on network performance in Mobile Ad Hoc Networks (MANETs). This was demonstrated by simulating various MANET scenarios using Network Simulator-2 (NS-2) with enhanced capability by adding propagation loss models (e.g., modified Two-Ray Ground model, ITU Line of Sight and Nonline of Sight (ITU-LoS and NLoS) model into street canyons and combined path loss and shadowing model (C-Shadowing)). The simulation results were then compared with the original Two-Ray Ground (TRG) model already available intoNS-2. The scenario primarily simulated was that of a mobile environment using Random Way Point (RWP) mobility model with a variable number of obstacles in the simulation field (such as buildings, etc., causing variable attenuation) in order to analyze the extent of communication losses in various propagation loss models. Performance of the Ad Hoc On-demand Distance Vector (AODV) routing protocol was also analyzed in an ad hoc environment with 20 nodes.

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De Beelde, Brecht, Emmeric Tanghe, Claude Desset, André Bourdoux, David Plets, and Wout Joseph. "Office Room Channel Modeling and Object Attenuation at Sub-THz Frequencies." Electronics 10, no. 14 (July 18, 2021): 1725. http://dx.doi.org/10.3390/electronics10141725.

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Large bandwidths are needed to meet the high-throughput requirements of future wireless communication systems. These larger bandwidths are available at mmWave and sub-THz frequencies, such as the V-band ranging from 50 to 75 GHz and the D-band ranging from 110 to 170 GHz. In this paper, we present channel measurements in an office environment, covering the full D-band. Line-of-Sight (LOS) path loss (PL) is modeled as a function of frequency and distance. Both a single-frequency floating-intercept and multi-frequency alpha-beta-gamma model provide a good fit to the measured LOS PL data. Attenuation due to blockage of the LOS path by various desk objects, such as computer peripherals and cables, is determined, as well as attenuation due to plant obstructions. Attenuation due to an obstructed LOS path ranges from 3 dB for a single universal serial bus (USB) cable, and up to 25 dB for a laptop power supply, computer mouse, computer monitor, or plant. Because of a higher diffraction angle, the measured attenuation is higher when the distance between the antennas decreases. We measure diffraction around a computer monitor for dual polarization and verify whether communication via the reflected non Line-of-Sight path makes high-throughput wireless communication possible when the LOS path is blocked.

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Habib, Karim, Maged Gouda, and Karim El-Basyouny. "Calibrating Design Guidelines using Mental Workload and Reliability Analysis." Transportation Research Record: Journal of the Transportation Research Board 2674, no. 8 (June 20, 2020): 360–69. http://dx.doi.org/10.1177/0361198120928075.

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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.

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Pein, Wayne. "Bicyclist Performance on a Multiuse Trail." Transportation Research Record: Journal of the Transportation Research Board 1578, no. 1 (January 1997): 127–31. http://dx.doi.org/10.3141/1578-16.

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Bicyclist crossing time from a full stop was measured using video recording equipment at 16 diverse trail-roadway intersections (two to six lanes, stop or signal controlled, divided or undivided) of the Pinellas Trail in Pinellas County, Florida. A total of 442 bicyclists (single individuals or randomly selected individuals from a group) were timed. The cruising speed of 65 bicyclists was also determined. A linear regression model was fit to the time and crossing-distance data. A linear regression was also fit to eight 85th percentile crossing-time points that were calculated from grouped raw data. Using kinematic physics, in which bicycle acceleration and intersection crossing velocity are variables, a theoretical equation was derived to predict bicyclist crossing time for any distance. This derived equation is a linear function of distance, so the regression coefficients could then be used to estimate bicyclist crossing velocity and acceleration on the Pinellas Trail. These estimated values for bicyclist acceleration and intersection crossing velocity compare favorably with the scant available data from foreign and domestic sources. Thus, the crossing-time prediction equation can be a useful tool when designing intersections for bicyclists, with application in signal timing and crossing-sight distance calculations.

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Luo, Qinghua, Kexin Yang, Xiaozhen Yan, Jianfeng Li, Chenxu Wang, and Zhiquan Zhou. "An Improved Trilateration Positioning Algorithm with Anchor Node Combination and K-Means Clustering." Sensors 22, no. 16 (August 15, 2022): 6085. http://dx.doi.org/10.3390/s22166085.

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As a classic positioning algorithm with a simple principle and low computational complexity, the trilateration positioning algorithm utilizes the coordinates of three anchor nodes to determine the position of an unknown node, which is widely applied in various positioning scenes. However, due to the environmental noise, environmental interference, the distance estimation error, the uncertainty of anchor nodes’ coordinates, and other negative factors, the positioning error increases significantly. For this problem, we propose a new trilateration algorithm based on the combination and K-Means clustering to effectively remove the positioning results with significant errors in this paper, which makes full use of the position and distance information of the anchor nodes in the area. In this method, after analyzing the factors affecting the optimization of the trilateration and selecting optimal parameters, we carry out experiments to verify the effectiveness and feasibility of the proposed algorithm. We also compare the positioning accuracy and positioning efficiency of the proposed algorithm with those of other algorithms in different environments. According to the comparison of the least-squares method, the maximum likelihood method, the classical trilateration and the proposed trilateration, the results of the experiments show that the proposed trilateration algorithm performs well in the positioning accuracy and efficiency in both light-of-sight (LOS) and non-light-of-sight (NLOS) environments. Then, we test our approach in three realistic environments, i.e., indoor, outdoor and hall. The experimental results show that when there are few available anchor nodes, the proposed localization method reduces the mean distance error compared with the classical trilateration, the least-squares method, and the maximum likelihood.

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Hagstotz, Steffen, Robert Reischke, and Robert Lilow. "A new measurement of the Hubble constant using fast radio bursts." Monthly Notices of the Royal Astronomical Society 511, no. 1 (January 12, 2022): 662–67. http://dx.doi.org/10.1093/mnras/stac077.

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ABSTRACT Fast radio bursts (FRBs) are very short and bright transients visible over extragalactic distances. The radio pulse undergoes dispersion caused by free electrons, along the line of sight, most of which are associated with the large-scale structure (LSS). The total dispersion measure therefore increases with the line of sight and provides a distance estimate to the source. We present the first measurement of the Hubble constant using the dispersion measure – redshift relation of FRBs with identified host counterpart and corresponding redshift information. A sample of nine currently available FRBs yields a constraint of $H_0 = 62.3 \pm 9.1 \, \rm {km} \, \rm {s}^{-1}\, \rm {Mpc}^{-1}$, accounting for uncertainty stemming from the LSS, host halo, and Milky Way contributions to the observed dispersion measure. We discuss possible biases arising from highly dispersed signals, and break the degeneracy between the expansion rate and the mean free electron abundance with a prior on the physical baryon density. The main current limitation is statistical, and we estimate that a few hundred events with corresponding redshifts are sufficient for a per cent measurement of H0. This is a number well within reach of ongoing FRB searches. We perform a forecast using a realistic mock sample to demonstrate that a high-precision measurement of the expansion rate is possible without relying on other cosmological probes. FRBs can therefore arbitrate the current tension between early and late-time measurements of H0 in the near future.

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Journal articles on the topic 'Available sight distance'

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