Spatial analysis of geometric design consistency and road sight distance

Because of the high number of crashes occurring on highways, it is necessary to intensify the search for new tools that help in understanding their causes. This research explores the use of a geographic information system (GIS) for an integrated analysis, taking into account two accident-related factors: design consistency (DC) (based on vehicle speed) and available sight distance (ASD) (based on visibility). Both factors require specific GIS software add-ins, which are explained. Digital terrain models (DTMs), vehicle paths, road centerlines, a speed prediction model, and crash data are integrated in the GIS. The usefulness of this approach has been assessed through a study of more than 500 crashes. From a regularly spaced grid, the terrain (bare ground) has been modeled through a triangulated irregular network (TIN). The length of the roads analyzed is greater than 100 km. Results have shown that DC and ASD could be related to crashes in approximately 4% of cases. In order to illustrate the potential of GIS, two crashes are fully analyzed: a car rollover after running off road on the right side and a rear-end collision of two moving vehicles. Although this procedure uses two software add-ins that are available only for ArcGIS, the study gives a practical demonstration of the suitability of GIS for conducting integrated studies of road safety

A comprehensive methodology for the analysis of highway sight distance

As one of the main elements of geometric design, sight distance must be considered carefully for the safe and efficient operation of highways. An application developed on geographic information systems (GIS) was con-ceived for the three-dimensional estimation of sight distance on highways, as opposed to conventional two-dimensional techniques, which may underestimate or overestimate the actual visibility conditions. It is capable of computing the available sight distance of a highway section given the driver?s eye height, the target height, the vehicle path and an elevation model. The outcome can be studied in detail with the aid of the tools and capabilities developed, including sight-distance graphs. The influence of the input features, such as the nature of the elevation model, its resolution and the spacing between path stations on the results accuracy was ana-lyzed. The interpretation of results is also essential to explain sight distance deficiencies and provide insight into the effect of roadside elements on those results. In addition, the sight-distance graph permits the detec-tion and characterization of sight-hidden dips, an undesirable shortcoming in the spatial alignment of high-ways. The versatility of GIS enables, moreover, an integrated research of highway safety. It allows the incor-poration of diverse operational factors such as accident data, traffic volume, operating speed and design con-sistency to detect and diagnose potentially hazardous spots or, eventually, identify the factors involved in a particular accident. This paper describes the methodology utilized and reviews the main issues through case study examples

Influence of headlamp lighting parameters on nighttime sight distance

Despite the higher accident rates during night driving compared to those in daylight, little research has been conducted on nighttime highway safety. Nighttime sight distance is one of the most relevant factors in night driving. Current design guides provide two dimensional models to study nighttime sight distance in order to design sag vertical curves. These models may, nonetheless, underestimate or overestimate the available sight distance because they do not take account of possible combinations with hor izontal alignment nor the actual roadside obstructions. It is therefore necessary to develop a three-dimensional (3D) procedure capable of analyzing the available sight distance under nighttime conditions. This way, it is possible to set the basis of nighttime driving safety research. Thus the study of nighttime sight distance could help in determining whether highway geometric design or headlamp features may influence accident-prone locations. The aim of this study is to analyze the influence of the headlamp lighting parameters on real highways and compare the nighttime sight distance outcome to that in daylight. A GIS-based application for sightdistance studies with a specific tool for nighttime sight distance has been used. The headlamp parameters studied were beam range, headlamp height, upward divergence angle and horizontal spread angle. The analysis has been carried out on different real highways, which enabled the study of the influence of each parameter on different 3D alignments

Reliability-based analysis of sight distance modelling for traffic safety

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

Addressing sight-distance-related safety effects of installing median barriers at horizontal curves of undivided highways under a 3D approach

Concrete barriers are often installed to separate opposing directions of traffic at hazardous horizontal curves on undivided highways in order to avoid frequent types of crashes such as head-on collisions. Whereas this treatment is effective for preventing head-on crashes, they reduce the available sight distance (ASD). The estimation of sight distance is usually performed under a two-dimensional (2D) approach, despite the three-dimensional (3D) nature of facilities. Radius curve, clearance and trajectory location on cross section are the only variables considered under the planar approach, ignoring the spatial component. To overcome this limitation, this study applies a 3D sight distance estimation method, where the sight distance reduction caused by installing barriers is evaluated, contemplating their shape and position in a detailed fully 3D model. The procedure facilitates incorporating mass standardized constructive elements into the highway model. This method consists of a geoprocessing model on a geographic information system (GIS), where the impact of the terrain, the roadway itself, and the road furniture on sight distance is broached. The results evidenced that the ASD outcomes were different under either approach. In addition, the ASD fell below the required stopping sight distance (SSD) of the standards under either approach. A potential application of this method is the analysis of the overall safety effects and the subsequent evaluation of crash modification factors associated to this safety measure

Distancia de visibilidad en carreteras: Influencia de modelos digitales de elevaciones y elementos de las márgenes

La distancia de visibilidad juega un papel importante en la seguridad vial de las carreteras. Se pueden emplear dos clases de modelos digitales de elevaciones (MDE) en el cálculo de la visibilidad disponible en carreteras: modelos digitales del terreno (MDT) y modelos digitales de superficie (MDS). Los MDT, que representan la superficie del terreno sin vegetación, se suelen utilizar para calcular la distancia de visibilidad disponible en fase de proyecto de la carretera. Por otra parte, el empleo de MDS proporciona información adicional acerca de los elementos de las márgenes, tales como árboles, construcciones, muros o incluso señales de tráfico que pueden reducir la distancia de visibilidad disponible. Este documento analiza la influencia del empleo de tres tipos de MDE en el cálculo de la distancia de visibilidad disponible. Para ello se han estudiado carreteras de distintas características de la Comunidad de Madrid (España) utilizando una aplicación informática basada en sistemas de información geográfica. El estudio realizado pone de manifiesto la influencia del tipo de MDE en los resultados de distancia de visibilidad, así como los pros y contras de la utilización de dichos modelos

A methodology for sight distance analysis on highways, alignment coordination, and their relation to traffic safety

El diseño geométrico de las carreteras es un factor de máxima importancia para la seguridad de la circulación. En este sentido, la distancia de visibilidad es una herramienta fundamental tanto para establecer criterios de diseño geométrico de carreteras de nueva planta como para evaluar el trazado de carreteras ya existentes. Las técnicas existentes de estimación de la distancia de visibilidad disponible producen resultados que pueden subestimar o sobreestimar la distancia de visibilidad disponible. En pocos casos se han aplicado sobre carreteras existentes métodos de alto rendimiento y probada precisión, y ninguno de ellos se ha aplicado a estudiar la relación con la seguridad viaria. La relación de la visibilidad disponible con la seguridad viaria no siempre es clara y la literatura muestra diversidad de resultados. El presente trabajo desarrolla una metodología para el estudio de la distancia de visibilidad en tres dimensiones con el fin analizar el trazado de las carreteras desde el punto de vista de la seguridad viaria. A tal efecto, se aprovecha el alto rendimiento de un sistema de información geográfica, donde es posible llevar a cabo un análisis integral (visibilidad, consistencia, intensidad de tráfico, accidentes, etc.). En total se han examinado 11 tramos de carretera de calzada única y un tramo de autopista. Primero se ha estudiado la relación entre distancia de visibilidad disponible y distancia de visibilidad de parada con distintos modelos de elevaciones, constatando que el empleo de modelos digitales de elevaciones que consideran, además del terreno, otros elementos como vegetación, dotaciones viarias o edificaciones, producen resultados más verosímiles. Las diferencias halladas entre los valores de distancia visibilidad disponible de los distintos modelos empleados fueron estadísticamente significativas. A continuación se han empleado estos resultados conjuntamente con la teoría de fiabilidad para abordar el estudio de las implicaciones de la visibilidad disponible sobre la seguridad viaria. Se presentan dos métodos con la visibilidad de parada como función de estado límite para calcular la probabilidad de fallo, incorporando las variables implicadas mediante un enfoque probabilístico frente a los modelos deterministas clásicos todavía vigentes en el diseño geométrico de carreteras. El primer método plantea un estudio continuo de la visibilidad de parada a lo largo de un tramo de carretera. El segundo método analiza la visibilidad de parada en curvas en planta a partir de la visibilidad disponible obtenida en dos y tres dimensiones. Se ha observado que las diferencias en los resultados de probabilidad de fallo, derivadas de cada una de las técnicas de estimación de la visibilidad empleadas, las diferencias son aún más significativas que en los valores de visibilidad disponible. Los resultados de éste último análisis se utilizan además para ajustar un modelo lineal generalizado en curvas en planta que permita evaluar el riesgo de accidente por distancia de visibilidad insuficiente. Las variables de probabilidad y exposición empleadas resultaron estadísticamente significativas. Finalmente se aborda la coordinación tridimensional del trazado en carreteras y sus posibles implicaciones en la seguridad viaria. En primer lugar se ha estudiado el efecto del uso de distintos modelos de elevaciones tanto en la detección de estos defectos del diseño como en los valores de los parámetros que los caracterizan en carreteras de calzada única. Además se han identificado las variables de coordinación tridimensional del trazado que propician la existencia de reapariciones del trazado con mayor frecuencia y su relación con los parámetros característicos. Por otro lado, la coordinación del trazado en autopistas, donde los elementos de la planta, del alzado y la sección transversal tienen dimensiones mayores, se estudia para desarrollar criterios de diseño que permitan evitar la aparición de los principales defectos relacionados con la distancia de visibilidad y la perspectiva de la carretera. Geometric design is a factor of the utmost importance in highway safety. In this regard, sight distance is a fundamental principle to establish criteria both for the geometric design of new highways and to evaluate the alignment of in‐service highways. The outcome of most current sight distance estimation methods may underestimate or overestimate the available sight distance. Only in a few cases, high‐performance methods of proven accuracy have been applied to in‐service highways, and none of them has been applied to establish linkage between sight distance and highway safety. Moreover, the relationship between sight distance and highway safety is not always clear and the literature shows diversity of results. The present work develops a methodology for the study of sight distance in three dimensions in order to assess the alignment of in‐service highways through sight distance, from the point of view of highway safety. For that purpose, the high performance of a geographic information system is exploited, where more comprehensive analyses can be performed (including sight distance, design consistency, traffic volume, collision frequency, etc.). In total, 11 two‐lane rural highways and a motorway section have been examined. First, the difference between the available sight distance and the stopping sight distance has been studied considering different elevation models as inputs. It was observed that the use of digital elevation models that comprise other elements besides the bare ground, such as vegetation, road furniture or buildings, produce more lifelike results. The differences between the available sight distance values on the models used were found to be statistically significant. These results were then used in conjunction with reliability theory to research the implications of available sight distance on highway safety. Two methods are presented contemplating the difference between the available sight distance and the stopping sight distance as the LSF to compute the probability of non‐compliance. The variables involved are incorporated by means of a probabilistic approach instead of the classical deterministic models still in force in highway geometric design standards. The first method conducted a continuous study of the stopping sight distance along a highway section. The second one analyzes the stopping sight distance in horizontal curves from the available sight distance outputs in two and three dimensions. It was observed that the differences in the probability of non‐compliance results, derived from each of the modelling methods contemplated, are statistically even more significant than in the values of the available sight distance. The results of the latter method are also used to fit a generalized linear model in horizontal curves that enables the evaluation of the accident risk caused by insufficient available sight distance. The probability and exposure variables used were statistically significant. Finally, the three‐dimensional alignment coordination of highways and its possible implications on traffic safety are broached. For two‐lane highways, the effect of the use of different elevation models on both the detection of these design shortcomings and on their characteristic parameter values was studied. In addition, the alignment coordination variables which most often favor the existence of sight‐hidden dips have been identified as well as their relation to the characteristic parameters. On the other hand, the three‐dimensional alignment coordination of motorways, where the horizontal and vertical alignments and the cross section are larger, is studied to develop design criteria that prevent the appearance of the main spatial alignment deficits related to sight distance and the perspective of the motorway

Undergraduate Student Performance in a Structural Analysis Course: Continuous Assessment before and after the COVID-19 Outbreak

The COVID-19 pandemic situation in 2020 forced educational institutions worldwide to fully adopt online learning for both teaching and assessment. However, this change may lead to less satisfactory learning outcomes, if the online technologies used have not been adequately applied. This study compares student engagement and performance through online continuous assessment in a one-semester structural analysis course for undergraduate architecture students before and after the pandemic outbreak. Online continuous assessment assignments had already been deployed and validated in the course evaluation system before the outbreak, and they were further leveraged during the online course. These assignments consisted of three weekly Moodle questionnaires throughout each of the fifteen course weeks, which determined the continuous assessment score. More than 200 students participated in each period. The results showed that shifting to online education affected continuous assessment outcomes very little in terms of participation rates and student performance. The possible underlying causes for the slight differences found between the two academic years are also discussed. The results highlight the robustness of the continuous assessment method used and emphasize the importance of having developed and validated online learning procedures to broach learning activities if contingency situations are required

Three-Dimensional Virtual Highway Model for Sight-Distance Evaluation of Highway Underpasses

When it comes to the safe design and operation of highways, sight distance is of utmost importance. The estimation of sight distance must be performed taking the three-dimensional (3D) nature of roadways and related features into account. Horizontal curves and crest vertical curves were the common sight restrictions considered in highway design. However, overhanging features may also affect sight distance. This paper presents a 3D virtual model for evaluating sight distance on sites where overpass structures restrict sight distance and for detecting sight-distance-related issues. The procedure and inputs for the computation of sight distance are described as are the results, which were validated and applied to a case study of an in-service highway underpass. Stopping sight distance and passing sight distance were evaluated for a section of highway with specific sight-distance characteristics of overpasses. The effect of the observer and target heights on sight distance for underpasses proved the opposite of those on horizontal curves and crests. Near an overpass, the heights should be switched from those used on curves and crests to evaluate stopping and passing sight distance according to operational and safety criteria. Finally, the currently existing passing zones were evaluated by means of the results obtained, revealing possible deficiencies in the establishment of passing zones

Driver glare exposure with different vehicle frontlighting systems

Introduction: Highway safety performance at night has received less attention in research than daytime, despite the higher accident rates occurring under night-time conditions. This study presents a procedure to assess the potential hazard for drivers created by headlight glare and its interaction with the geometric design of highways. Method: The proposed procedure consists of a line-of-sight analysis performed by a geoprocessing model in geographic information systems to determine whether the rays of light that connect headlights and oncoming drivers are obstructed by either the roadway or its roadsides. Then, the procedure checks whether the non-obstructed rays of light are enclosed by a given headlight beam. Different hypotheses were set concerning the headlight beam features, including the horizontal spread angle and whether the headlights are fixed or swiveling. A highway section was selected to test and validate the procedure proposed. A 3D recreation of the highway and its environment derived from a LiDAR point cloud was used for this purpose. Results: The findings disclose how glare is produced on tangents, horizontal curves, transitions between them and sequences of curves. The effect of visual obstructions conveniently placed is also discussed. Conclusions: A greater glare incidence is produced as the horizontal headlights spread angle increases. Swiveling headlights increase glare on highways left curves and reduce it on right curves. Practical Applications: The procedure and conclusions of this study can contribute to develop more effective glare avoidance technologies as well as identify and assess glare-prone sections. The glare evaluation assists in evaluating glare countermeasures such as deciding whether to place a vegetation barrier and where