Papers by Alejandra Medina
Perspectives on Public Management and Governance, 2020
This article provides a systematic review of the network formation literature in the public secto... more This article provides a systematic review of the network formation literature in the public sector. In particular, we code and categorize the theoretical mechanisms used in empirical network research to motivate collaboration and tie formation. Based on a review of the 107 articles on network formation found in 40 journals of public administration and policy from 1998 to 2019, we identify 15 distinct theoretical categories. For each category, we describe the theory, highlight its use in the literature, and identify limitations and concerns with current applications. Overall, we find that most studies rely on a similar set of general theories of network formation. More importantly, we find that most theoretical mechanisms are not well specified, and empirical tests are often unable to directly assess the specific underlying mechanism. The results of our review highlight the need for our field to embrace experimental designs, develop panel network datasets, and engage in more network-...
2002Final reportMoyer, Joseph; Inman, Vaughn W.PDFTech ReportFHWA-RD-02-003Driver errorsUnited St... more 2002Final reportMoyer, Joseph; Inman, Vaughn W.PDFTech ReportFHWA-RD-02-003Driver errorsUnited States. Federal Highway AdministrationWierwille, Walter W.Hanowski, Richard J.Hankey, Jonathan M.Kieliszewski, C. A.Lee, Suzanne E.Medina, A.Dingus, Thomas A.Virginia Polytechnic Institute and State University. Transportation InstituteUnited States. Federal Highway AdministrationNTL-SAFETY AND SECURITY-Human FactorsFederal Highway AdministrationDriver error is cited as a contributing factor in most automobile crashes, and although estimates vary by source, driver error is cited as the principal cause of from 45 to 75 percent of crashes. However, the specific errors that lead to crashes, and the nature of driver error contributions to crash circumstances often cannot be specified. Rather, driver error has been used as a catchall category When machine failures have been ruled out. This report describes an effort to gather more specific information about the driver errors that lead to crashes, the relative influences that various driver errors have in causing crashes, and the degree to which current infrastructure features may contribute driver errors. This project's objectives were to: (1) develop driver error taxonomies, (2) identify the causes of errors within taxonomic categories, (3) gather data to further develop these taxonomies, and (4) provide recommendations for improvements to traffic control devices, roadway delineations, and accident reporting forms. This report summarizes the tasks that were conducted in support of these project objectives. One highlight of the project was a site surveillance effort in which video cameras recorded over 1,200 traffic events caused by driver error. Analysis of these events included the development of infrastructure-based countermeasures to reduce the number of incidents caused by driver error
Transportation Research Record: Journal of the Transportation Research Board, 2020
Crashes involving roadway objects can cause severe injuries and property damage. Utilizing data f... more Crashes involving roadway objects can cause severe injuries and property damage. Utilizing data from the Second Strategic Highway Research Program (SHRP 2) naturalistic driving study (NDS), this study investigated crashes involving roadway objects and their implications for the potential of machine vision-based driving systems in preventing such crashes. A comprehensive statistical and machine learning analysis was first conducted to identify major factors affecting the occurrence and severity of such events. Machine vision performance metrics (based on the SHRP 2 NDS cameras) and human driving decisions were then analyzed to identify opportunities where machine vision systems could particularly mitigate risk factors. The results suggest that driver behaviors/errors, speed, reaction time, and object characteristics played the most significant role in the occurrence and severity outcome of the SHRP 2 events. The average object detection distance based on the SHRP 2 cameras was approx...
This document is the final report for NCHRP Project 15-41, “Sag Vertical Curve Design Criteria fo... more This document is the final report for NCHRP Project 15-41, “Sag Vertical Curve Design Criteria for Headlight Sight Distance.” This report includes a review of the current methodologies used in the design of sag vertical curves, a review of the changes in headlamp technologies, the results of the survey of practitioners, two visibility experiments, and discussion on potential changes to the American Association of State Highway and Transportation Officials (AASHTO) design guide. The review of the headlamp technology shows that, over time, headlamp technologies have had increasing limitation on the amount of light emitted above the horizontal axis of the headlamp. In addition to the regulatory impact, headlamp technologies such as visually optically aligned technologies also limit uplight. In the practitioner survey, it was found that very few deviations from the AASHTO design methodologies were used. Based on the practitioner review, the potential to modify the current methodologies is limited to the manipulation of the vehicle speed, deceleration, and the angle of curvature change. The results of the visibility experiments found that participants detected objects at distances which were significantly shorter than the safe stopping distance (SSD). This occurred not only in sag vertical curves, but also on flat roadway. This indicated that even if sag vertical curves were redesigned, visibility distance would still be shorter than SSD because the headlamps would be the limiting factor. A review of the potential modifications to sag vertical curve designs (which were suggested as a result of the practitioner survey) found that these changes would be inadequate to make up the difference between visibility distance and SSD.
According to statistics compiled by the National Highway Traffic Safety Administration (NHTSA), 4... more According to statistics compiled by the National Highway Traffic Safety Administration (NHTSA), 4,229 fatalities and 90,000 injuries resulted from crashes involving heavy trucks in 2008 (1). In regard to rear-end crashes, heavy trucks were 3.2 times more likely than light vehicles to be struck in the rear in fatal multiple-vehicle crashes (1). The Federal Motor Carrier Safety Administration (FMCSA) contracted with the Virginia Tech Transportation Institute (VTTI) to perform a General Estimates System (GES) crash database analysis on rear-end collisions involving heavy trucks using data from 2006 as part of the Enhanced Rear Signaling for Heavy Trucks project (2). Findings indicated that there were 23,508 rear-end crashes involving heavy trucks which resulted in 135 fatalities, 1,603 incapacitating injuries, 2,074 non-incapacitating injuries, and 2,711 possible injuries. The three most common rear-end crash configurations where a heavy truck was struck from behind were: (i) the heavy...
Revista alergia Mexico (Tecamachalco, Puebla, Mexico : 1993)
Polyarteritis nodosa is a diffuse vasculitis of small- and medium-sized muscular arteries that ca... more Polyarteritis nodosa is a diffuse vasculitis of small- and medium-sized muscular arteries that can involve the vessels of one or several organ systems. We report an 11-year-old boy with severe atopic dermatitis further complicated with erythroderma and cerebellar symptoms. Laboratory studies showed negative antinuclear antibodies and antineutrophil cytoplasmic antibodies; increased serum complement, IgG cryoglobulins 96.8 mg/dL (0-80) and serum IgG 2,160 mg/dL (613-1,295), and positive alpha-cardiolipin test. The IgE value was high. Skin prick tests and RAST were positive for dust mites and casein. The viral profile was negative. Imaging studies disclosed tortuousity in the vessels and ischemic infarction in the cerebellum and thalamus. A diagnosis of polyarteritis nodosa with central nervous system involvement was made. The patient improved with immunosuppressive therapy and thalidomide. Currently, the patient is controlled and in a rehabilitation program. Other cases of polyarteri...
Journal of Safety Research, 2015
Introduction: Large truck crashes have significantly declined over the last 10 years, likely due,... more Introduction: Large truck crashes have significantly declined over the last 10 years, likely due, in part, to the increased use of onboard safety systems (OSS). Unfortunately, historically there is a paucity of data on the real-world efficacy of these devices in large trucks. The purpose of this study was to evaluate the two OSSs, lane departure warning (LDW) and roll stability control (RSC), using data collected from motor carriers. Method: A retrospective cohort approach was used to assess the safety benefits of these OSSs installed on Class 7 and 8 trucks as they operated during normal revenue-producing deliveries. Data were collected from 14 carriers representing small, medium, and large carriers hauling a variety of commodities. The data consisted of a total of 88,112 crash records and 151,624 truck-years that traveled 13 billion miles over the observation period. Results: The non-LDW cohort had an LDW-related crash rate that was 1.917 times higher than the LDW cohort (p = 0.001), and the non-RSC cohort had an RSC-related crash rate that was 1.555 times higher than the RSC cohort (p b 0.001). Conclusions: The results across analyses indicated a strong, positive safety benefit for LDW and RSC under real-world conditions. Practical applications: The results support the use of LDW and RSC in reducing the crash types associated with each OSS.
Journal Oral Of Research, 2012
ARTÍCULO ORIGINAL / ORIGINAL ARTICLE ¿Predicen los requisitos de ingreso a odontología el rendimi... more ARTÍCULO ORIGINAL / ORIGINAL ARTICLE ¿Predicen los requisitos de ingreso a odontología el rendimiento académico durante primer año? Do admission requirements to dentistry predicts the academic performance over the first year? Resumen: Introducción: Al tener claridad respecto de cuáles son los predictores de desempeño académico, se puede mejorar la selección de los estudiantes que ingresan a la universidad asegurando que estén en posesión de las competencias necesarias que garanticen un buen rendimiento. Objetivos: Determinar la capacidad predictiva de los requisitos de ingreso y del proceso PSU, para el rendimiento académico de los alumnos de primer año de la carrera de odontología. Material y Método: Estudio observacional descriptivo de corte transversal con alumnos que cursaron primer año entre el 2004-2008 (inclusive). Se revisó las planillas de ingreso de la Unidad de Admisión y Registro Académico Estudiantil (UDARAE) obteniendo información referida al género, año de ingreso, promedio de notas de enseñanza media (NEM), puntaje de selección (PSU-SEL) y puntajes de las pruebas de lenguaje (PSU-L), matemáticas (PSU-M) y ciencias (PSU-C). Para el rendimiento académico se consultó las planillas de notas de la Oficina de Registro y Control de la Facultad. Resultados: El mayor porcentaje de aporte a la explicación del rendimiento académico correspondió al promedio NEM, con 10%, luego la PSU-C, con 5,6%. Las PSU-L y PSU-M arrojaron un 0% de aporte y el PSU-SEL un 23,4%. Conclusiones: La variable que más fuertemente se asocia con el rendimiento académico es el promedio NEM, seguido por la PSU-C. Tanto la PSU-L como la PSU-M presentaron una capacidad predictiva nula. El proceso PSU presentó una capacidad predictiva limitada.
Transportation Research Record: Journal of the Transportation Research Board, 2011
Two microscopic simulation methods are compared for driver behavior: the Gazis–Herman–Rothery (GH... more Two microscopic simulation methods are compared for driver behavior: the Gazis–Herman–Rothery (GHR) car-following model and a proposed agent-based neural network model. To analyze individual driver characteristics, a back-propagation neural network is trained with car-following episodes from the data of one driver in the naturalistic driving database to establish action rules for a neural agent driver to follow under perceived traffic conditions during car-following episodes. The GHR car-following model is calibrated with the same data set, using a genetic algorithm. The car-following episodes are carefully extracted and selected for model calibration and training as well as validation of the calibration rules. Performances of the two models are compared, with the results showing that at less than 10-Hz data resolution the neural agent approach outperforms the GHR model significantly and captures individual driver behavior with 95% accuracy in driving trajectory.
Proceedings Title: Proceedings of the 2012 Winter Simulation Conference (WSC), 2012
This paper presents a research effort aimed at modeling normal and safety-critical driving behavi... more This paper presents a research effort aimed at modeling normal and safety-critical driving behavior in traffic under naturalistic driving data using agent based modeling techniques. Neuro-fuzzy reinforcement learning was used to train the agents. The developed agents were implemented in the VISSIM simulation platform and were evaluated by comparing the behavior of vehicles with and without agent behavior activation. The results showed very close resemblance of the behavior of agents to driver data.
2007 IEEE Intelligent Transportation Systems Conference, 2007
In the absence of advanced traveler information systems, commuters tend to select their routes of... more In the absence of advanced traveler information systems, commuters tend to select their routes of travel, within a congested network, primarily based on historical average travel times. Typical traffic conditions can be sufficient if a specific day is similar to these average conditions. However, if traffic conditions vary considerably from the norm, historical information may not be sufficient for commuters
Transportation Research Record: Journal of the Transportation Research Board, 2008
Adequate spacing and design of access to crossroads in the vicinity of freeway ramps are critical... more Adequate spacing and design of access to crossroads in the vicinity of freeway ramps are critical in the safety and traffic operations of the freeway, crossroad, and properties near interchanges. Research attempted to develop a methodology to evaluate the safety impact of different access-road spacing standards. Results clearly demonstrate the shortcomings of the AASHTO standards and the benefits of enhancing these standards. The models developed as part of this research effort were used to compute the crash rate associated with alternative section spacing. The study demonstrates that the models satisfied the statistical requirements and provide reasonable crash estimates. Results demonstrate an eightfold decrease in the crash rate over an access-road spacing ranging from 0 to 300 m. An increase in the minimum spacing from 90 m (300 ft) to 180 m (600 ft) results in a 50% reduction in the crash rate. The developed models provide an excellent tool to evaluate the trade-off of alternat...
Transportation Research Record, 2004
During the course of an FHWA-sponsored research project, driver errors in crashes and near-crashe... more During the course of an FHWA-sponsored research project, driver errors in crashes and near-crashes (i.e., critical incidents) were investigated, and an analysis approach was developed with which to identify infrastructure-related and non-infrastructure-related problems at intersections and other roadway sites. Referred to as a specific site critical incident analysis, this analysis approach consisted of four general steps: ( a) selection of a site, ( b) careful review of the site's critical-incident data, ( c) determination of the potential critical-incident contributing factors, and ( d) identification of incident clusters. An incident cluster is a group of critical incidents with similar characteristics that occur at the same location. From these incident clusters, researchers gained insight into potential infrastructure-related and non-infrastructure-related causal factors associated with critical incidents and, subsequently, could redesign solutions. An overview is presented...
Transportation Research Record: Journal of the Transportation Research Board, 1999
A case study in which the researchers developed a prototype low-volume roads pavement management ... more A case study in which the researchers developed a prototype low-volume roads pavement management system (PMS) using a geographic information system (GIS) platform for Fountain Hills, Arizona, is described. The approach used and the problems faced are discussed. The first stage of the study entailed the collection of all information available from the city. City engineers provided a database with inventory and condition data, and an AutoCAD map of the city streets. The research team then evaluated several software packages. They selected the Road Surface Management System (RSMS) package developed at Arizona State University for the PMS portion. This program was developed to help local Arizona agencies systematically manage low-volume road and street pavements. The researchers evaluated two GIS packages for the study, based on the software’s capabilities and the city’s needs. They selected Maplnfo because it was less expensive and easier to learn. A menu-driven MapInfo application tha...
Transportation Research Record: Journal of the Transportation Research Board, 1998
The development of a formula to prioritize pavement rehabilitation projects based on experts’ opi... more The development of a formula to prioritize pavement rehabilitation projects based on experts’ opinion is presented. This formula is used for the preparation of the Arizona Department of Transportation (ADOT) 5 yr pavement preservation program. The knowledge to determine the prioritization formula and treatment assignment criteria was captured from a group of experts using a survey design based on the rational factorial methodology. The survey questionnaire provided a set of pavement sections with different characteristics and asked the experts to indicate which sections should receive a rehabilitation treatment, what type of treatment they would recommend for each section, and which priority should be assigned to the resulting preservation project. Eight pavement characteristics (functional classification, geographical region, structural number, traffic, pavement rideability, cracking, rutting, and average maintenance cost for the past 3 yr) were identified as influence variables. A...
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Papers by Alejandra Medina