2 + 1 Highways: Overview and Future Directions

Most of the rural transportation system is composed of two-lane highways, and many of them serve as the primary means for rural access to urban areas and freeways. In some highways, traffic volumes can be not high enough to justify a four-lane highway but higher than can be served by isolated passing lanes, or can present high number of head-on collisions. In those conditions, 2 + 1 highways are potentially applicable. This type of highway is used to provide high-performance highways as intermediate solution between the common two-lane highway and the freeway. Successful experiences reported in Germany, Sweden, Finland, Poland, or Texas (US) may suggest that they are potentially applicable in other countries. The objective of this white paper is to provide an overview of the past practice in 2 + 1 highways and discuss the research directions and challenges in this field, specially focusing on, but not limited to, operational research in association with the activities of the Subcommittee on Two-Lane Highways (AHB40 2.2) of the Transportation Research Board. The significance of this paper is twofold: (1) it provides wider coverage of past 2 + 1 highways design and evaluation, and (2) it discusses future directions of this field.The authors wish to thank the Fundación Agustín de Betancourt from the Universidad Politécnica de Cartagena for funding the research

Análisis de la funcionalidad del tráfico en carreteras convencionales en función de la distribución y características de sus zonas de adelantamiento

[EN] Two-lane highways must be safe for the motorists, but they also need to provide operational efficiency. The Spanish geometric design standards indicate that the desirable proportion of passing zones is 40% of the total length for each travel direction; and passing zones should be evenly distributed. The standards indirectly expect to accommodate the design hourly volume. The Highway Capacity Manual (HCM 2010) methodology is used in Spain to evaluate traffic operation and quality of service. Three performance measures are used in two-lane highways: average travel speed; percent time spent following; and, percent free flow. The effect of passing is considered through adjustment factors to average speed and percent time spent following. They depend on the percentage of no passing zones and were obtained through simulations in TWOPAS, which was calibrated with field data from the 70's. The PhD thesis develops and analyzes in detail two-lane highways performance measures and the effect of passing zones. To do so, current passing behavior was documented. The analysis included performance measures at one section of the highway and effectiveness of passing zones. Then, TWOPAS was calibrated and validated using genetic algorithms. The model was applied to an ideal two-lane highway varying directional traffic flow, directional split, percentage of no passing zones and average passing zone length. More than 300000 scenarios were evaluated. The analysis allowed to develop technical criteria to adequately include passing zones in two-lane highways considering their operational impacts. Moreover, the HCM 2010 methodology was adapted to Spanish driver behavior.[ES] Las vías deben ser seguras para todos sus usuarios, pero también deben satisfacer la demanda de tráfico con un nivel de servicio aceptable. En la normativa española de diseño geométrico se indica que en las carreteras convencionales el porcentaje de zonas de adelantamiento deseable es del 40% por cada sentido de circulación y debe estar lo más uniformemente repartido posible, para asegurar su adecuada funcionalidad, y se propone la metodología del Manual de Capacidad americano (HCM 2010) para su estimación. El HCM 2010 basa la calidad del tráfico en tres medidas de desempeño: la velocidad media, el porcentaje de tiempo en cola y el porcentaje de velocidad libre. En ellas, el efecto de las zonas de adelantamiento se traduce en unos coeficientes de ajuste en función del porcentaje de zona de adelantamiento no permitido a lo largo del segmento. Estos coeficientes no dependen de la distribución y las características de las zonas de adelantamiento, a pesar de que pueden modificar el comportamiento del tráfico. Además, se desarrollaron en base a simulaciones calibradas con datos americanos de los años setenta. La presente Tesis Doctoral desarrolla y profundiza el análisis de medidas de desempeño de tráfico en carreteras convencionales, en concreto el efecto que las zonas de adelantamiento tienen en ellas, para la evaluación de su funcionalidad. Para ello, se tomaron datos experimentales en zonas de adelantamiento en España y se evaluaron, por un lado, las medidas de desempeño en la sección de carretera y por otro lado, la efectividad de las zonas de adelantamiento. Asimismo, se calibra por primera vez a las condiciones españolas un microsimulador de tráfico con algoritmos genéticos, a partir de los datos observacionales, y se aplica a nuevas configuraciones, variando características geométricas (porcentaje de zona de adelantamiento, longitud media de las zonas de adelantamiento y su distribución) y de tráfico (volumen direccional, reparto y porcentaje de pesados). Así, se puede determinar la afección de las zonas de adelantamiento en la funcionalidad de un segmento de carretera. Todo ello ha permitido, por un lado, el desarrollo de criterios técnicos para la adecuada inclusión de zonas de adelantamiento en el diseño geométrico de una carretera convencional, y por otro lado, la propuesta de una metodología para evaluar la calidad del tráfico en carreteras convencionales españolas.[CA] Les carreteres han de ser segures per a tots els seus usuaris, però també han de satisfer la demanda de tràfic amb un nivell de servici acceptable. En la normativa espanyola de disseny geomètric s'indica que a las carreteres convencionals, el percentatge de zones d'avançament permès desitjable és del 40% per cada sentit de circulació. Les zones han de estar repartides tan uniformement com siga possible, per tal d'assegurar la seua funcionalitat. Es proposa la metodologia del Manual de Capacitat americà (HCM 2010) per a la seua estimació. El HCM 2010 basa la qualitat del tràfic en tres mesures de rendiment: la velocitat mitjana, el percentatge de temps en cola i el percentatge de velocitat lliure. L'efecte de les zones d'avançament en aquelles mesures es tradueix en l'ús d'uns coeficients d'ajust en funció del percentatge de zones d'avançament permès al llarg del segment. Aquests coeficients no depenen ni de la distribució ni de les característiques de les zones d'avançament, factors que podrien modificar el comportament del tràfic. A més, els coeficients es van desenvolupar en base a simulacions calibrades amb dades americanes dels anys setanta. La present Tesi Doctoral desenvolupa i profunditza en l'anàlisi de les mesures de rendiment del tràfic en carreters convencionals. Concretament, en l'efecte que les zones d'avançament tenen en elles, per tal d'avaluar la seua funcionalitat. Per tot allò, es van obtenir dades experimentals en zones d'avançament d'Espanya, i es van avaluar, d'una banda, les mesures de rendiment en la secció de la carretera, i d'altra, l'efectivitat de les zones d'avançament. També es va calibrar, per primera vegada, un microsimulador de tràfic amb les condicions espanyoles i emprant algoritmes genètics. El model calibrat es va aplicar a noves configuracions de segments de carretera, variant les seues característiques geomètriques (percentatges de zones d'avançament permès, longitud mitjana de les zones i distribució al llarg del segment) i de tràfic (volum direccional, repartiment i percentatge de vehicles pesats). D'aquesta manera es va poder determinar l'afecció de les zones d'avançament en la funcionalitat d'un segment de carretera. Tot allò ha permès, d'una banda, el desenvolupament de criteris tècnics per incloure de manera adequada les zones d'avançament en el disseny geomètric d'una carretera convencional. D'altra banda, s'ha proposat una metodologia per avaluar la qualitat del tràfic a les carreteres convencionals espanyoles.Moreno Chou, AT. (2015). Análisis de la funcionalidad del tráfico en carreteras convencionales en función de la distribución y características de sus zonas de adelantamiento [Tesis doctoral]. Editorial Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/49618TESI

Daytime and Nighttime Passing Maneuvers on a Two-Lane Rural Road in Spain

[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.Llorca Garcia, C.; Moreno Chou, AT.; García García, A.; Pérez Zuriaga, AM. (2013). Daytime and Nighttime Passing Maneuvers on a Two-Lane Rural Road in Spain. Transportation Research Record. (2358):3-11. doi:10.3141/2358-01S311235

Operational effectiveness of passing zones depending on their length and traffic volume

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.Moreno Chou, AT.; Llorca Garcia, C.; García García, A.; Pérez Zuriaga, AM. (2013). Operational effectiveness of passing zones depending on their length and traffic volume. Transportation Research Record. (2395):57-65. doi:10.3141/2395-07S57652395Romana, M. G. (1999). Passing Activity on Two-Lane Highways in Spain. Transportation Research Record: Journal of the Transportation Research Board, 1678(1), 90-95. doi:10.3141/1678-12Al-Kaisy, A., & Freedman, Z. (2010). Estimating Performance on Two-Lane Highways. Transportation Research Record: Journal of the Transportation Research Board, 2173(1), 72-79. doi:10.3141/2173-09Al-Kaisy, A., & Karjala, S. (2010). Car-Following Interaction and the Definition of Free-Moving Vehicles on Two-Lane Rural Highways. Journal of Transportation Engineering, 136(10), 925-931. doi:10.1061/(asce)te.1943-5436.0000148Al-Kaisy, A., & Durbin, C. (2011). Platooning on Two-lane Two-way Highways: An Empirical Investigation. Procedia - Social and Behavioral Sciences, 16, 329-339. doi:10.1016/j.sbspro.2011.04.454Gattis, J. L., Alguire, M. S., Townsend, K., & Rao, S. (1997). Rural Two-Lane Passing Headways and Platooning. Transportation Research Record: Journal of the Transportation Research Board, 1579(1), 27-34. doi:10.3141/1579-04Dixon, M. P., Sarepali, S. S. K., & Young, K. A. (2002). Field Evaluation of Highway Capacity Manual 2000 Analysis Procedures for Two-Lane Highways. Transportation Research Record: Journal of the Transportation Research Board, 1802(1), 125-132. doi:10.3141/1802-15Polus, A., & Cohen, M. (2009). Theoretical and Empirical Relationships for the Quality of Flow and for a New Level of Service on Two-Lane Highways. Journal of Transportation Engineering, 135(6), 380-385. doi:10.1061/(asce)0733-947x(2009)135:6(380)Rozenshtein, S., Polus, A., & Cohen, M. (2012). Models for Estimating Drivers following on Two-Lane Rural Highways. Transportation Research Record: Journal of the Transportation Research Board, 2286(1), 68-75. doi:10.3141/2286-08Al-Kaisy, A., & Durbin, C. (2008). Evaluating new methodologies for estimating performance on two-lane highways. Canadian Journal of Civil Engineering, 35(8), 777-785. doi:10.1139/l08-020Llorca, C., & García, A. (2011). Evaluation of Passing Process on Two-Lane Rural Highways in Spain with New Methodology Based on Video Data. Transportation Research Record: Journal of the Transportation Research Board, 2262(1), 42-51. doi:10.3141/2262-0

Development of a new microscopic passing maneuver model for two-lane rural roads

Microsimulation is a useful tool to analyze traffic operation. On two-lane highways, the complexity of passing and the interaction with oncoming traffic requires specific models. This study focused on the development of a passing desire, decision and execution model. Results of the observation of 1752 maneuvers on 10 rural roads in Spain were used for this development. The model incorporated the effect of new factors such as available sight distance, delay and remaining travel time until the end of the highway segment. Outputs of the model were compared to observed data: firstly, individual passing maneuvers; secondly, traffic flow, percent followers and number of passing maneuvers in four single passing zones with two different traffic levels. The model was validated in four alternative passing zonesData collection was part of the research project "Desarrollo de modelos de distancias de visibilidad de adelantamiento", funded by the Spanish Ministry of Economy and Competitiveness, with reference number TRA2010-21736. Authors wish to thank Spanish General Directorate of Traffic, Spanish Ministry of Public Works, Valencia Regional Department of Transport and Valencia Province Road Department, for their collaboration in the field study.Llorca Garcia, C.; Moreno Chou, AT.; Lenorzer, A.; Casas, J.; García García, A. (2015). Development of a new microscopic passing maneuver model for two-lane rural roads. Transportation Research Part C: Emerging Technologies. 52:157-172. doi:10.1016/j.trc.2014.06.001S1571725

Desarrollo de competencias transversales y evaluación de su adquisición en el Grado en Ingeniería Civil

[EN] The Vice-Rectorate for Studies, Quality and Acreditation and the Institute of Education Sciences promotes that education is based on competencies, either generic or specific. The School of Civil Engineering of the Universitat Politècncia de València has chosen the course “Caminos y Aeropuertos” to evaluate the generic competencies “Team working and leadership” and “Effective communication”, both oral and written. The course “Caminos y Aeropuertos” is a core subject in third year of the Deegree in Civil Engineering. The teaching methodology of this technical subject is based on the active participation of students through a diverse set of assignments. This paper explains the adaptation of the methodology to include the evaluation of generic competencies, having a high number of students (124). It is based on written exercises in teams of 1, 2 and 4 students, as well as on an oral presentation.[ES] Desde el Vicerrectorado de Estudios, Calidad y Acreditación de la Universitat Politècnica de València, junto con el Instituto de Ciencias de la Educación, se está llevando a cabo un proyecto para dar un giro hacia la formación basada en competencias. En la Escuela Técnica Superior de Ingenieros de Caminos, Canales y Puertos, se ha elegido la asignatura "Caminos y Aeropuertos" como punto de control para la evaluación de las dimensiones competenciales "Trabajo en Equipo y Liderazgo" y "Comunicación Efectiva", incluyendo comunicación oral y escrita. “Caminos y Aeropuertos” es una asignatura de carácter troncal impartida en tercer curso del Grado en Ingeniería Civil, con una base claramente técnica. Desde su concepción, su docencia se ha diseñado con base en metodologías activas. No obstante, ha sido necesario modificar ligeramente su metodología docente para incluir la evaluación de las competencias mencionadas. En este trabajo se muestra cómo se ha adaptado la metodología docente y cómo se ha procedido a la evaluación de estas competencias dentro de una asignatura eminentemente técnica y con un alto número de alumnos matriculados (124). La metodología se basa principalmente en la realización de trabajos escritos de diferente entidad en grupos de 1, 2 y 4 personas y una exposición oral.Pérez Zuriaga, AM.; Llorca García, C.; Moreno Chou, AT. (2015). Desarrollo de competencias transversales y evaluación de su adquisición en el Grado en Ingeniería Civil. En In-Red 2015 - CONGRESO NACIONAL DE INNOVACIÓN EDUCATIVA Y DE DOCENCIA EN RED. Editorial Universitat Politècnica de València. https://doi.org/10.4995/INRED2015.2015.1616OC

Optimization-based assisted calibration of traffic simulation models

Use of traffic simulation has increased in recent decades; and this high-fidelity modelling, along with moving vehicle animation, has allowed transportation decisions to be made with better confidence. During this time, traffic engineers have been encouraged to embrace the process of calibration, in which steps are taken to reconcile simulated and field-observed performance. According to international surveys, experts, and conventional wisdom, existing (non-automated) methods of calibration have been difficult or inadequate. There has been extensive research on improved calibration methods, but many of these efforts have not produced the flexibility and practicality required by real-world engineers. With this in mind, a patent-pending (US 61/859,819) architecture for software-assisted calibration was developed to maximize practicality, flexibility, and ease-of-use. This architecture is called SASCO (i.e. Sensitivity Analysis, Self-Calibration, and Optimization). The original optimization method within SASCO was based on "directed brute force" (DBF) searching; performing exhaustive evaluation of alternatives in a discrete, user-defined search space. Simultaneous Perturbation Stochastic Approximation (SPSA) has also gained favor as an efficient method for optimizing computationally expensive, "black-box" traffic simulations, and was also implemented within SASCO. This paper uses synthetic and real-world case studies to assess the qualities of DBF and SPSA, so they can be applied in the right situations. SPSA was found to be the fastest method, which is important when calibrating numerous inputs, but DBF was more reliable. Additionally DBF was better than SPSA for sensitivity analysis, and for calibrating complex inputs. Regardless of which optimization method is selected, the SASCO architecture appears to offer a new and practice-ready level of calibration efficiency. (C) 2015 Elsevier Ltd. All rights reserved.Hale, DK.; Antoniou, C.; Brackstone, M.; Michalaka, D.; Moreno Chou, AT.; Parikh, K. (2015). Optimization-based assisted calibration of traffic simulation models. Transportation Research Part C: Emerging Technologies. 55:100-115. doi:10.1016/j.trc.2015.01.018S1001155

Operational Considerations of Passing Zones for Two-lane Highways: Spanish Case Study

[EN] The U.S. Highway Capacity Manual (HCM 2010) methodology is used in Spain to evaluate traffic operation and quality of service. In two-lane undivided highways, the effect of limiting where drivers could pass slower vehicles, or passing restrictions, is considered through the percentage of no-passing zones. This measure does not account for how passing opportunities are distributed along the road. The objective of this research was to evaluate the effect percentage of no-passing zones and average passing zone length on two-lane, and incorporate them in the analysis methodology, if significant. The TWOPAS microsimulation program was calibrated and validated to the Spanish conditions. Passing restrictions had little effect on average traffic speed (ATS), with differences lower than 6 km/h between a segment of road with no passing restrictions and a segment of a road with 100% of length with passing restriction. Conversely, passing restrictions can increase percent time spent following (PTSF) up to 30%. Increasing the passing zone length beyond 2,000 m does not improve PTSF. The new models could be used to better estimate traffic operation on Spanish two-lane highways.The research was funded by the Spanish Ministry of Economy and Competitiveness [TRA2013-42578-P], and has been partially developed as a result of a mobility stay at the University of Florida funded by the Spanish Ministry of Economy and Competitiveness [EEBB-I-15-09970]. The research was completed with the support of the FPI Research and Teaching Fellowship of the Spanish Ministry of Economy and Competitiveness [BES-2011-044612] and the TUM University Foundation Fellowship (TUFF) for international postdocs. We would like to thank Dr. Lemke from the Bundesanstalt fur Strassenwesen (Federal Highway Research Institute) for providing the final report of the research project FE 16.0015/2009 (23). This work was supported by the German Research Foundation (DFG) and the Technical University of Munich (TUM) in the framework of the Open Access Publishing Program.Moreno Chou, AT.; Llorca Garcia, C.; Washburn, S.; Bessa Jr., JE.; García García, A. (2018). Operational Considerations of Passing Zones for Two-lane Highways: Spanish Case Study. PROMET - Traffic&Transportation. 30(5):601-612. https://doi.org/10.7307/ptt.v30i5.2776S60161230

Speed Table Evaluation and Speed Modeling for Low-Volume Crosstown Roads

More than 50% of injury accidents in Spain take place on crosstown roads in urban areas. Traffic calming is an initiative to reduce the impact of traffic on local streets by lowering both the number and the severity of crashes. However, the implementation of traffic-calming devices in Spain was not standardized in the past, and no technical criteria were applied. The paper presents the methodology, results, and conclusions of an analysis specifically related to speed tables, which are flat-topped speed humps, as part of the research project MODETRA. For the research, five low-volume crosstown roads with 16 speed tables were selected to analyze drivers' behavior. Speed data were collected from a sample of more than 900 vehicles through the selected crosstown roads using Global Positioning System trackers. For each individual vehicle, a continuous speed profile along the path was obtained. The analysis showed that the minimum speed occurred when the vehicle left the traffic-calming device and the maximum deceleration occurred just before the device. Geometric characteristics of the speed tables were measured by using a digital profilometer. A wide dispersion in the geometry can be concluded. It was found that the speed reduction depended mainly on the separation between traffic-calming devices, whereas the speed over the speed tables depended crucially on the entrance-ramp slope, the speed table length, and the distance from the previous traffic control device. Also, no statistical correlations were found between speed table height and speed reduction or spot speed over the speed table.The authors thank the Center for Studies and Experimentation of Public Works of the Spanish Ministry of Public Works, which subsidized the research. They also thank the Infrastructure and Transportation Department, General Directorate of Public Works, Valencian Government, Spain, and the Ministry of the Interior, General Directorate of Traffic, Spain, for their cooperation during data collection.Moreno Chou, AT.; García García, A.; Romero Rojas, MA. (2011). Speed Table Evaluation and Speed Modeling for Low-Volume Crosstown Roads. Transportation Research Record. 2203(1):85-93. doi:10.3141/2203-11S859322031Hallmark, S. L., Hawkins, N., Fitzsimmons, E., Resler, J., Plazak, D., Welch, T., & Petersen, E. (2008). Use of Physical Devices for Calming Traffic along Major Roads through Small Rural Communities in Iowa. Transportation Research Record: Journal of the Transportation Research Board, 2078(1), 100-107. doi:10.3141/2078-14Zuriaga, A. M. P., García, A. G., Torregrosa, F. J. C., & D’Attoma, P. (2010). Modeling Operating Speed and Deceleration on Two-Lane Rural Roads with Global Positioning System Data. Transportation Research Record: Journal of the Transportation Research Board, 2171(1), 11-20. doi:10.3141/2171-0

DEVELOPMENT AND VALIDATION OF SPEED KIDNEY, A NEW TRAFFIC CALMING DEVICE

Traffic calming has been widely applied to urban areas in recent decades to moderate speed and traffic volume. Because most measures used are physical, a vehicle must modify its path and speed. A benefit of traffic calming is improved safety from speed reduction and traffic volume reduction. However, traffic calming has disadvantages, such as emergency response delays, traffic diversion, noise, vibrations, damage to vehicles, and discomfort. Common traffic-calming devices do not consider discomfort for drivers who achieve an appropriate calmed and safe speed. Consequently, it was necessary to develop a new traffic-calming device to moderate speed and to minimize the disadvantages of the previous devices. The Highway Engineering Research Group of the Polytechnic University of Valencia, Spain, has invented, designed, and developed a new traffic-calming device, Speed Kidney. This paper provides the objectives of the Speed Kidney, a description of the new traffic-calming device, and its geometric design. The technological development of the device is described, as are the main results from preliminary tests, implementation on a campus street, and implementation on a controlled test track. Implementation criteria are also given. The Speed Kidney is a functional, feasible, sustainable, and safe solution for traffic calming.The authors thank the Center for Studies and Experimentation of Public Works of the Spanish Ministry of Public Works and the Education Department, Valencian Government, Spain, which subsidized the research. The authors also thank the company Pavasal E.C. for cooperation on the implementation and the improvement of the constructive method. Finally, the test site could not have been constructed without the loan of the site from the Ministry of Public Works, Spain, and the collaboration of the company Abertis.García García, A.; Moreno Chou, AT.; Romero Rojas, MA. (2011). DEVELOPMENT AND VALIDATION OF SPEED KIDNEY, A NEW TRAFFIC CALMING DEVICE. Transportation Research Record. (2223):43-63. doi:10.3141/2223-06S43632223Barbosa, H. M., Tight, M. R., & May, A. D. (2000). A model of speed profiles for traffic calmed roads. Transportation Research Part A: Policy and Practice, 34(2), 103-123. doi:10.1016/s0965-8564(98)00067-6García, A., & Romero, M. (2009). Discussion of «Video-Capture-Based Approach to Extract Multiple Vehicular Trajectory Data for Traffic Modeling» by Heng Wei, Chuen Feng, Eric Meyer, and Joe Lee. Journal of Transportation Engineering, 135(3), 149-150. doi:10.1061/(asce)0733-947x(2009)135:3(149