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[EN] The presence of cyclists on Spanish rural roads is ever increasing and currently frequent, and thus becoming a serious safety concern. In rural environments, the risk of a crash is higher than in rural areas. The main cause is the higher speed of motor vehicles during overtaking manoeuvres. This manoeuvre is especially challenging when cyclists ride in groups as they may change size, length, shape, and speed along their route. These variables and those related to road cross-section can influence driver behaviour when overtaking a group of cyclists. To study this, instrumented bicycles were used to ride along five road segments with different geometric and traffic characteristics. Cyclists rode individually and in groups. Overtaking was evaluated by analysing the lateral distance, the speed, and other characteristics of the manoeuvre. Wider roads presented higher lateral clearances and overtaking speeds. Narrower roads had a high opposing lane invasion but a high level of compliance with the minimum lateral clearance. A higher clearance and lower speed of overtaking vehicles was registered when cyclists rode in line. Compliance with the 1.5 m clearance depended on the group configuration, being higher when cyclists rode in line. However, overtaking cyclists riding two abreast presented more accelerative manoeuvres, especially on narrow roads., This research is part of the research project TRA2016-80897-R, funded by MCIN/AEI/10.13039/501100011033 and the research project SPIP2017-02280, funded by the General Directorate of Traffic of Spain.

[EN] In Spain, the presence of cyclists' groups riding on two-lane rural roads in a single file or in parallel line is growing. The number of overtaking maneuvers to them is also increasing. This is one of the most dangerous interactions between motor vehicles and bicycles. However, the risk of these maneuvers has not been analyzed in depth. This research analyzes the objective and subjective risk of overtaking maneuvers to cyclists' groups. During this maneuver, the motorized vehicle overtakes the bicycles with a certain speed and lateral distance. These are the surrogate measures used to analyze the objective risk, whereas the subjective risk was analyzed based on the subjective risk perception that 10 cyclists riding instrumented bicycles (in different group configurations) indicated when every motor vehicle overtook them. Results show that the cyclists most exposed to the overtaking maneuver are those at the front and at the rear of the group. In relation to the configuration, the risk is higher in parallel lines, as the lateral clearance is lower compared with a single line. It is even higher when the overtaking maneuver is flying, which is usually performed at higher speeds and lower lateral clearance. The subjective risk perception increases with higher speed and lower lateral clearance, and is higher at the rear positions. Overtaking in which lateral distance is less than 1.5 m is perceived as the riskiest. These results provide scientific recommendations to enhance safety for cyclists' groups, and to integrate cycling with vehicular traffic on two-lane rural roads, The author(s) disclosed receipt of the following financial support for the research, authorship, and/or publication of this article: The study presented in this paper is part of the research project titled "Road safety countermeasures for two-lane rural roads with group of cyclists (Safe4Bikes)'' (SPIP2017-02280), subsidized by the Direccion General de Trafico (General Directorate of Traffic) of Spain. Document

[EN] In 2014, highway vehicles accounted for 72.8% of all Greenhouse Gases emissions from transportation in Europe. In the United States (US), emissions follow a similar trend. Although many initiatives try to mitigate emissions by focusing on traffic operations, little is known about the relationship between emissions and road design. It is feasible that some designs may increase average flow speed and reduce accelerations, consequently minimizing emissions. This study aims to evaluate the impact of road horizontal alignment on CO2 emissions produced by passenger cars using a new methodology based on naturalistic data collection. Individual continuous speed profiles were collected from actual drivers along eleven two-lane rural road sections that were divided into 29 homogeneous road segments. The CO2 emission rate for each homogeneous road segment was estimated as the average of CO2 emission rates of all vehicles driving, estimated by applying the VT-Micro model. The analysis concluded that CO2 emission rates increase with the Curvature Change Rate. Smooth road segments normally allowed drivers to reach higher speeds and maintain them with fewer accelerations. Additionally, smother segments required less time to cover the same distance, so emissions per length were lower. It was also observed that low mean speeds produce high CO2 emission rates and they increase even more on roads with high speed dispersions. Based on this data, several regression models were calibrated for different vehicle types to estimate CO2 emissions on a specific road segment. These results could be used to incorporate sustainability principles to highway geometric design., The study presented in this paper is part of the research project titled "CASEFU - Estudio experimental de la funcionalidad y seguridad de las carreteras convencionales" (TRA2013-42578-P), subsidized by the Spanish Ministry of Economy, Industry, and Competitiveness and the European Social Fund. In addition, the authors would like to thank the Center for Studies and Experimentation of Public Works (CEDEX) of the Spanish Ministry of Public Works for subsidizing the field data collection and the General Directorate of Public Works and Transportation of the Valencian Government, to the Road Department of the Valencian Provincial Council, and to the Spanish Ministry of the Interior, especially the General Directorate of Traffic of Spain, for their cooperation in field data gathering. Finally, we would like to thank Professor Hesham A. Rakha, Virginia Tech (USA), for providing the VT-Micro model and assessing the authors in its use to obtain outcomes.

[EN] 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., The authors thank the Polytechnic University of Valencia, which subsidized the research project CONSIM-Desarrollo de un Modelo para la Evaluacion de la Consistencia del Diseno Geometric de Carreteras Convencionales Mediante Simuladores de Conduccion. The study presented here was also part of the research project titled CASEFU-Estudio Experimental de la Funcionalidad y Seguridad de las Carreteras Convencionales, which was subsidized by the Spanish Ministry of Economy and Competitiveness and the European Social Fund.

[ES] La cantidad de estudios de seguridad vial basados en simuladores de conducción está en continuo crecimiento. En este sentido, la Universitat Politècnica de València (UPV) ha desarrollado un simulador de conducción de bajo coste: SE2RCO (Simulador para la Evaluación, Entrenamiento y Rehabilitación de Conductores). El principal objetivo de la investigación es la validación de este simulador, con el fin de desarrollar estudios relacionados con la seguridad vial y el diseño geométrico de carreteras incorporando el factor humano. Dicha validación se ha realizado a partir de la observación en campo de los perfiles continuos de velocidad desarrollados por 28 voluntarios conduciendo su propio vehículo en un tramo de carretera convencional de 30 km. Los mismos voluntarios condujeron posteriormente en el simulador de conducción ese mismo tramo de carretera reconstruido en un entorno virtual. Un total de 79 curvas y 52 rectas fueron objeto de análisis. La comparación entre las velocidades desarrolladas en la realidad y las observadas durante la simulación permitieron llevar a cabo la validez objetiva del simulador de conducción. 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 operación, se observó que la velocidad real era aproximadamente 5 km/h menor que la simulada. Finalmente, estos resultados estuvieron apoyados por la percepción de los conductores, ya que la mayoría de ellos evaluaron la calidad del entorno simulado y el grado de similitud entre la tarea de conducción real y simulada como medio o alto, consiguiendo de esta manera la validez subjetiva del simulador de conducción., Los autores quisieran agradecer a la Universitat Politècnica de València (UPV), que financió el proyecto de investigación “CONSIM - Desarrollo de un Modelo para la Evaluación de la Consistencia del Diseño Geométrico de Carreteras Convencionales mediante Simuladores de Conducción” (PAID 05-2012). Asimismo, agradecer también al Ministerio de Economía y Competitividad y al Fondo Social Europeo, que financiaron el proyecto de investigación “CASEFU - Estudio experimental de la funcionalidad y seguridad de las carreteras convencionales” (TRA2013-42578-P), del cual forma parte este estudio.

Overtaking is one of the most dangerous manoeuvres on two-lane rural highways. The most influential factors are related to drivers, so ITS and assistance systems are not yet common. This research is based on experimental data of overtaking manoeuvres collected using an instrumented passenger car, equipped with four cameras, laser rangefinders and a global positioning service (GPS) tracker. This vehicle was driven along four different road segments in the surroundings of Valencia (Spain) at a speed slightly slower than the operating speed of each segment. Overtaking time and speeds were measured. Unlike previous work, the influence of human factor was also considered. Age and gender of overtaking driver, as well as time spent following were used to characterise this influence. More than 200 manoeuvres were recorded and the influence of driver characteristics and delay on gap acceptance, manoeuvre duration and speed differences have been analysed. Results show differences in behaviour between age and gender groups, since young male overtaking drivers have shown a more aggressive behaviour. Overtaking times were around 1 s lower than other drivers, whereas average speed difference was 4 km/h higher. Collected data and their analysis have provided a basis to review design criteria and to develop future assistance systems., Authors would like to thank Spanish Ministry of Economy and Competitiveness that subsidizes the research project with reference code TRA2010-21736. Authors thank also Spanish General Traffic Directorate, Spanish Ministry of Public Works and Valencia Regional Governance for their collaboration during field study.

[EN] Passing is one of the most complex driving maneuvers performed on two-lane rural roads and has important effects on road safety and traffic operation. Passing is affected by driving behavior, road geometry, traffic volume, and traffic composition as well as external factors. Research was developed to compare the passing process under daytime and nighttime conditions. An experimental method was designed to collect video data of passing maneuvers on a two-lane rural road segment located near Valencia, Spain. Two methods were used: (a) external observations of four passing zones with six video cameras and (b) an instrumented vehicle equipped with video cameras and laser rangefinders, driven slightly below the operating speed along a segment of the same road so it would be passed by other vehicles. A total of 291 maneuvers were observed, up to 20% of which were at night. Macroscopic analysis results indicated that approximately 17% of passes were at night, even though passing frequency and passing demand decreased at night. Also, the behaviors of individual drivers who passed other vehicles were different at night and during the day. Maneuvers limited by the presence of an opposing vehicle were performed more quickly at night, even if the accepted gaps were longer. In this case, a more difficult perception of distances to opposing vehicles and of vehicle speeds explained the differences. In contrast, maneuvers limited by sight distance (without a visible opposing vehicle) were slower at night. This observation matched a traditional hypothesis: passing at night is safer because the headlights of an opposing vehicle allow a driver to anticipate the vehicle's position before it becomes visible., The authors thank the Spanish Ministry of Economy and Competitiveness for subsidizing the research project as well as the Spanish Ministry of Public Works and the Spanish General Traffic Directorate for collaboration during the field study.

The occurrence of road crashes depends on several factors, with design consistency (i.e., conformance of highway geometry to drivers' expectations) being one of the most important. A new consistency model for evaluating the performance of tangent-to-curve transitions on two-lane rural roads was developed. This model was based on the inertial consistency index (ICI) defined for each transition. The ICI was calculated at the beginning point of the curve as the difference between the average operating speed on the previous 1-km road segment (inertial operating speed) and the actual operating speed at this point. For the calibration of the ICI and its thresholds, 88 road segments, which included 1,686 tangent-to-curve transitions, were studied. The relationship between those results and the crash rate associated with each transition was analyzed. The results showed that the higher the ICI was, the higher the crash rate; thus, the probability of accidents increased. Similar results were obtained from the study of the relationship between the ICI and the weighted average crash rate of the corresponding group of transitions. A graphical and statistical analysis established that road consistency might be considered good when the ICI was lower than 10 km/h, poor when the ICI was higher than 20 km/h, and fair otherwise. A validation process that considered 20 road segments was performed. The ICI values obtained were highly correlated to the number of crashes that had occurred at the analyzed transitions. Thus, the ICI and its consistency thresholds resulted in a new approach for evaluation of consistency., The authors thank the Center for Studies and Experimentation of Public Works of the Spanish Ministry of Public Works, which partially subsidized the data collection, for obtaining the empirical operating speed profiles used in the validation process. The authors also thank the General Directorate of Public Works of the Infrastructure and Transportation Department of the Valencian government, the Valencian Province Council, and the General Directorate of Traffic of the Ministry of the Interior of the Government of Spain for their cooperation in data gathering.

Most studies on two-lane highway operations have focused on the percentage of following vehicles or the adjustment of the Highway Capacity Manual (HCM) procedure to local data. The HCM proposes the length of no-passing zones as a model parameter; however, the distribution and characteristics of passing zones are not addressed. In fact, only a few studies on the expected number of passes in a passing zone have been carried out. This research presents an analysis of the effectiveness of passing zones in terms of their length and traffic volume. Data were collected from four passing zones on a rural highway in Spain. The two-way traffic volumes ranged from 100 to 900 vehicles per hour (vph), and the passing zone lengths ranged from 265 to 1,270 m. More than 1,600 passing maneuvers were recorded. The operational effectiveness of the passing zones was obtained from the passing frequency and the passing rate. The results indicated that the longer the passing zone, the higher the passing frequency; however, the results stabilized with lengths above 1,100 m. Balanced flows with two-way traffic volumes between 600 and 700 vph optimized the number of passes. Nevertheless, the increase in the passing frequency with the traffic volume was lower than with the increase in following vehicles. The results were validated with data from another 12 passing zones. Finally, HCM adjustments based on the percentage of no-passing zones did not reliably represent the effectiveness of passing zones. Therefore, the effectiveness of every passing zone should be considered, and adjustment factors should be modified to maximize the passing opportunities for traffic volumes between 600 and 700 vph., The authors thank the Spanish Ministry of Science and Innovation, which subsidized the research project, and the Spanish Ministry of Public Works for its collaboration during the field study.

Methodologies based on naturalistic observation provide the most accurate data for studying drivers' behaviour. This study presents a new methodology to obtain naturalistic data related to drivers' behaviour in a road segment. It is based on the combination of using global positioning system data and drivers' questionnaires. The continuous speed profiles along a road segment and the characteristics of drivers, of their trips and the type of their vehicles can be obtained for a great amount of drivers. It has already been successfully used for several studies, such as the development of models to estimate operating speed profile in two-lane rural road segments; or the characterisation of driving styles. These operating speed models have been the key for the development of a new geometric design consistency model, allowing an easier road safety evaluation. Besides, knowledge on the human factors that influence speed choice may be useful for road safety media campaigns and education programs designers, and also for the improvement of intelligent driver assistance systems., The authors thank 'Centre for Studies and Experimentation of Public Works (CEDEX)' of the 'Spanish Ministry of Public Works' that partially subsidizes the research. We also wish to thank to the 'General Directorate of Public Works, Urban Projects and Housing' of the 'Infrastructure, Territory and Environment Department' of the 'Valencian Government', to the 'Valencian Provincial Council' and to the 'General Directorate of Traffic' of the 'Ministry of the Interior' for their cooperation in field data gathering.

[EN] In the road design process, speed variation along the road segment is an important issue to consider in adapting road geometry to drivers' expectations. To achieve this objective, speed criteria are used to evaluate road consistency. Being able to estimate the operating speed in the design phase can lead to safer road alignment. With this objective, several researchers have developed operating speed models. Most of these models are based on collected spot speed data. They assume constant speed on curves and, therefore, deceleration that occurs entirely on the approach tangent. According to these assumptions, spot speed data are collected at the center of the horizontal curve and at the midpoint of the preceding tangent to obtain operating speed models. This paper presents a new methodology based on the use of Global Positioning System devices that allow continuous collecting and processing of speed data. With this new methodology, not only can new and more accurate operating speed models he developed, but cited hypotheses can also be checked. Observed speed continuous profiles allow studies that previously could not be done, especially as related to deceleration and speed variations. This study calibrated new speed models, including three for horizontal curves with a radius curve and the curvature change rate of a single curve as explanatory variables, and one for tangents that incorporates the curve speed model. Tangent-curve speed variations are evaluated, with comparison of Delta(85)V and Delta V(85), analysis of the deceleration length occurring on a curve, and development of two deceleration models., The authors thank the Center for Studies and Experimentation of Public Works of the Spanish Ministry of Public Works, which partially subsidized the research. The authors also thank the Infrastructure and Transportation Department, General Directorate of Public Works, Valencian Government, Spain; the Valencian Provincial Council; and the Ministry of the Interior, General Directorate of Traffic, Spain, for their cooperation in field data gathering.