Francisco Javier Camacho-Torregrosa

New geometric design consistency model based on operating speed profiles for road safety evaluation

To assist in the on-going effort to reduce road fatalities as much as possible, this paper presents a new methodology to evaluate road safety in both the design and redesign stages of two-lane rural highways. This methodology is based on the analysis of road geometric design consistency, a value which will be a surrogate measure of the safety level of the two-lane rural road segment. The consistency model presented in this paper is based on the consideration of continuous operating speed profiles. The models used for their construction were obtained by using an innovative GPS-data collection method that is based on continuous operating speed profiles recorded from individual drivers. This new methodology allowed the researchers to observe the actual behavior of drivers and to develop more accurate operating speed models than was previously possible with spot-speed data collection, thereby enabling a more accurate approximation to the real phenomenon and thus a better consistency measurement. Operating speed profiles were built for 33 Spanish two-lane rural road segments, and several consistency measurements based on the global and local operating speed were checked. The final consistency model takes into account not only the global dispersion of the operating speed, but also some indexes that consider both local speed decelerations and speeds over posted speeds as well. For the development of the consistency model, the crash frequency for each study site was considered, which allowed estimating the number of crashes on a road segment by means of the calculation of its geometric design consistency. Consequently, the presented consistency evaluation method is a promising innovative tool that can be used as a surrogate measure to estimate the safety of a road segment.

Use of Heading Direction for Recreating the Horizontal Alignment of an Existing Road

A new method for fitting the horizontal alignment of a road to a set of (x, y) points is proposed in this article. The proposed method describes the horizontal alignment as a sequence of headings unlike current methods that represent road alignment through curvature.These points are obtained from digital imagery or global positioning system (GPS)-data collection. An analytic-heuristic approach is introduced and the proposed method produces unique solutions for complex horizontal alignments. Researchers and departments of transportation could obtain accurate geometric features using the solution. However, the solution may not be accurate enough for road redesign. The article presented case studies using the method.

Tangent-to-Curve Transition on Two-Lane Rural Roads Based on Continuous Speed Profiles

AbstractIn the road geometric design process, speed variation along the road segment is one of the most popular criteria to evaluate road consistency, hence the importance of estimating operating speed and its variations. Most of the estimation models are based on speed spot data collection, usually assuming some hypotheses like operating speed remains constant at curves and speed variations take place entirely at preceding tangent. This paper presents the results of the study of the deceleration phenomenon using a new methodology based on data collection by global positioning system devices. By means of this new methodology, not only new and more accurate models can be developed, but also the previous hypotheses can be checked and new studies can be carried out. Tangent-to-curve speed variations have been evaluated, comparing the 85th percentile speed differential (Δ85V) and the differential of the 85th percentile operating speed (ΔV85), analyzing the percentage of deceleration length that takes place at...

New Consistency Model Based on Inertial Operating Speed Profiles for Road Safety Evaluation

AbstractRoad crashes are mainly caused by three concurrent factors: infrastructure, vehicles, and human factors. The interaction between infrastructure and human factors leads to the concept of geo...

Validation of a Low-Cost Driving Simulator Based on Continuous Speed Profiles

The number of road safety studies that are based on driving simulators is growing significantly. The Polytechnic University of Valencia, Spain, developed a low-cost driving simulator for the assessment, training, and rehabilitation of drivers (SE2RCO). The main objective of this research was the validation of the driving simulator so that studies about road safety and highway geometric design that considered human factors could be performed. The validation was based on continuous speed profiles collected from 28 volunteers on a 30-km-long, two-lane rural road section. The same volunteers drove through the same road section built in SE2RCO. Speed data of 79 curves and 52 tangents were selected for the analysis. Comparison of the real and simulated speeds ensured the simulator’s objective validity according to average and operating speeds. Two models were developed to predict field speeds from simulated speeds. Results showed that a simulated average speed lower than approximately 90 km/h was linked to a similar real average speed. For higher simulated speeds, the average speed in the real environment was lower than the simulated one. In addition, the actual operating speed was around 5 km/h lower than the operating speed in the driving simulator. Most volunteers assessed the quality and similarity of the virtual environment compared with the real world as medium or high and assessed the driving tasks similarly, thus achieving subjective validation of the simulator.

Time-Based Calibration of the Inertial Operating Speed to Enhance the Assessment of the Geometric Design Consistency

Road crashes are mainly caused by three concurrent factors: infrastructure, vehicle, and human factors. The interaction between the infrastructure and human factors leads to the concept of geometric design consistency. Recently, a global consistency model was developed based on the difference between the inertial operating speed profile and the operating speed profile. The first was defined as the weighted average operating speed of the previous road section based on distance, and represents drivers’ expectancies, whereas the second represents road behavior. However, drivers’ expectancies are related to short-term memory which declines gradually and depends on time. Thus, a time-based inertial operating speed would allow a more accurate estimation of the phenomenon. This research analyzes different periods of time and weighting distributions to identify how drivers’ expectancies should be estimated. A set of 71 homogeneous road segments located in Italy were considered in the study. As a result, 25 seconds and a convex parabolic distribution should be used to calculate the inertial operating speed profile. This new way of estimating drivers’ expectancies showed better results than those obtained based on distance. Finally, the proposed consistency model was compared with the previous models and was found to be able to assess more accurately the geometric design consistency. Therefore, the proposed consistency model is a useful tool for engineers to estimate the number of crashes so that they can incorporate road safety considerations into the geometric design of either new two-lane rural roads, or improving the existing ones.

Examination of the Free-Flow Speed Distribution on Two-Lane Rural Roads

Free-flow speed variation of passenger vehicles along a road segment is one of the most used factors in road safety studies, as a surrogate measure to evaluate road design consistency. Free-flow speed may be measured when a road segment is already built but must be estimated during the design phase. Several studies have been carried out to calibrate models to estimate free-flow speed, with geometric features as explanatory variables. Currently, most free-flow speed models focus only on mean speed or speed in particular percentiles, such as the 85th or 95th. Moreover, most studies have assumed normality in the free-flow speed distribution without checking this hypothesis. The main objective of this study was to analyze the free-flow speed distribution on two-lane rural road curves and tangents. The research focused on two main issues: determining whether speed data were normally distributed at a specific site and analyzing the behavior of the mean and standard deviation of speed on curves and tangents. The study was based on continuous operating speed profiles, which were obtained from a database of more than 16,000 vehicles/km. A total of 63 horizontal curves and 78 tangents were analyzed. According to the results, the normal distribution is not the best distribution in most cases for describing free-flow speeds. In 46 of the curves and 64 of the tangents, free-flow speed cannot be assumed to be normally distributed. Therefore, some other distributions should be tested in further research.

ANÁLISIS DEL COMPORTAMIENTO DE CONDUCTORES EN CURVAS DE BAJO ÁNGULO DE DEFLEXIÓN

Las curvas con un bajo angulo de deflexion pueden ser un problema para la percepcion por parte de los conductores. Para evitar este aspecto, las diferentes normativas establecen criterios de desarrollo o radios minimos, que las haga apreciables por los conductores. Los criterios que estan incorporados en las normativas espanolas nunca tuvieron una base experimental cientifica sino fueron fruto de juicios tecnicos. Los objetivos de esta investigacion son analizar la percepcion subjetiva y caracterizar la respuesta de los usuarios de carreteras convencionales ante curvas de bajo angulo de deflexion, para conseguir unas recomendaciones de diseno para este tipo de curvas. Estas curvas se restituyen geometricamente con el objetivo de identificar cual servira para un posterior estudio mas detallado in situ. Para ello se presenta el diseno y desarrollo de un cuestionario online, el cual incorpora una base de datos de curvas de bajo angulo de deflexion presentes en carreteras convencionales espanolas. El cuestionario consiste en mostrar a un amplio numero de conductores una serie de videos aleatorios donde se visualiza, desde el punto de vista del usuario de la carretera, el recorrido de varias de las curvas. Tras este paso, los encuestados deben expresar su percepcion y comportamiento a traves de varias preguntas de tipo abierto y cerrado. Estos resultados quedan registrados en una base de datos, para su posterior filtrado, tratamiento e interpretacion estadistica. DOI: http://dx.doi.org/10.4995/CIT2016.2016.4118

Validación de un simulador de conducción de bajo coste para el diseño de carreteras convencionales

La cantidad de estudios de seguridad vial basados en simuladores de conduccion esta en continuo crecimiento. En este sentido, la Universitat Politecnica de Valencia (UPV) ha desarrollado un simulador de conduccion de bajo coste: SE 2 RCO (Simulador para la Evaluacion, Entrenamiento y Rehabilitacion de Conductores). El principal objetivo de la investigacion es la validacion de este simulador, con el fin de desarrollar estudios relacionados con la seguridad vial y el diseno geometrico de carreteras incorporando el factor humano. Dicha validacion se ha realizado a partir de la observacion en campo de los perfiles continuos de velocidad desarrollados por 28 voluntarios conduciendo su propio vehiculo en un tramo de carretera convencional de 30 km. Los mismos voluntarios condujeron posteriormente en el simulador de conduccion ese mismo tramo de carretera reconstruido en un entorno virtual. Un total de 79 curvas y 52 rectas fueron objeto de analisis. La comparacion entre las velocidades desarrolladas en la realidad y las observadas durante la simulacion permitieron llevar a cabo la validez objetiva del simulador de conduccion. Los resultados mostraron que la velocidad media en el simulador y en la realidad era similar cuando la velocidad simulada era inferior a 87.3 km/h. En caso de ser superior, la velocidad media en la realidad era menor que en el simulador. En cuanto a la velocidad de operacion, se observo que la velocidad real era aproximadamente 5 km/h menor que la simulada. Finalmente, estos resultados estuvieron apoyados por la percepcion de los conductores, ya que la mayoria de ellos evaluaron la calidad del entorno simulado y el grado de similitud entre la tarea de conduccion real y simulada como medio o alto, consiguiendo de esta manera la validez subjetiva del simulador de conduccion. DOI: http://dx.doi.org/10.4995/CIT2016.2016.3444