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

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

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

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

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

A methodology to measure sight-hidden dips'parameters.

Highway design standards specify several requirements on available sight distance. Usually, compliance with these standards is ensured during the design phase of a new road. This is made through geometric calculations that take into account the terrain and the road. In this paper, a procedure for measuring distances in an existing road from georeferenced photographs is proposed. In addition, an estimation of the error committed when using this procedure is made. Distances measured using this procedure arecompared with the ones measured using a Global Navigation Satellite System (GNSS). Distances error is within the error estimation and is low enough for using it in traffic safety studies. In addition, the procedure is applied to measure several parameters of a sight-hidden dip. This procedure does not need a terrain model to measure these parameters. This is an advantage compared with other existing procedures for estimating the parameters of sight-hidden dips

Evaluating Pedestrians' Safety on Urban Intersections: A Visibility Analysis

Overall visibility plays a key role in the safety of pedestrians. Despite its importance, verifying the right provisioning of sufficient available sight distances among pedestrians and vulnerable road users (VRUs) is not a prevalent practice. On top of that, the pursuit for more sustainable modes of transportation has promoted the establishment of different shared mobility services which are prone to increase walking and, thus, the number of pedestrians and other VRUs in urban settings. With the intention of verifying how car-centered designs perform for non-motorized users, a 3D procedure that evaluates the visibility of pedestrians and other users is presented and applied to specific cases in Madrid, Spain. The proposed solution employs virtual trajectories of pedestrians with mobility impairments and without them, cyclists, and personal transportation device riders. Their visibility was assessed around the functional area of urban intersections, including zones where possible jaywalking practices might occur. The evaluation was performed three-dimensionally, making use of LiDAR data, GIS tools, and 3D objects. Results show the impact of street furniture location on visibility, the distinctive influence of vegetation on the lines of sight of each observer, and how design parameters that were intended to improve motorized traffic could affect VRU

Suitability Testing of LiDAR Processing Software Aimed at 3-D Sight Distance Estimations

Sight distance estimations are significant components of road safety analyses. Drivers ought to have enough available sight distance (ASD) in order to safely perform basic driving maneuvers. When not performed in situ, estimating ASD on existing roads normally requires up-to-date representations of the roads’ geometric properties as well as the execution of roadway design related tasks and geospatial analysis operations; hence, several software products are needed to carry out these calculations throughout their entire workflow. Nowadays, LiDAR based Mobile Mapping Systems (MMS) have been intensively put into use to gather data needed to accomplish many transportation applications. In spite of their many benefits, MMS produce fair volumes of point cloud data which add some complexity to the processing stage in terms of software, computational requirements and interoperability. This paper analyses software capabilities, in terms of suitability and performance, of computer programs capable of LiDAR data processing tasks. The main goal of this evaluation is to gauge their aptness to deliver data needed to perform ASD estimations. To accomplish this, a thorough review of available literature on sight distance analyses was conducted to get a depiction of frequently demanded software tasks and deliverables and based on that, different volumes of point cloud were processed with a variety of software solutions in order to test their appropriateness for the purpose from early stages of the workflow to final calculations. This research highlights how the truly potential of LiDAR data for performing highway safety related analyses relies heavily upon the usage of efficient and powerful software tools

Sight distance studies on roads: influence of digital elevation models and roadside elements

Sight distance plays an important role in road traffic safety. Two types of Digital Elevation Models (DEMs) are utilized for the estimation of available sight distance in roads: Digital Terrain Models (DTMs) and Digital Surface Models (DSMs). DTMs, which represent the bare ground surface, are commonly used to determine available sight distance at the design stage. Additionally, the use of DSMs provides further information about elements by the roadsides such as trees, buildings, walls or even traffic signals which may reduce available sight distance. This document analyses the influence of three classes of DEMs in available sight distance estimation. For this purpose, diverse roads within the Region of Madrid (Spain) have been studied using software based on geographic information systems. The study evidences the influence of using each DEM in the outcome as well as the pros and cons of using each model