RESUMO
Numerous studies have previously used a variety of count-data models to investigate factors that affect the number of crashes over a certain period of time on roadway segments. Unlike past studies which deal with crash frequency, this study views the crash rates directly as a continuous variable left-censored at zero and explores the application of an alternate approach based on tobit regression. To thoroughly investigate the factors affecting freeway crash rates and the potentially temporal instability in the effects of crash factors involving traffic volume, freeway geometries and pavement conditions, a classic uncorrelated random parameters tobit (URPT) model and a correlated random parameters tobit (CRPT) model were estimated, along with a conventional fixed parameters tobit (FPT) model. The analysis revealed a large number of safety factors, including several appealing and interesting factors rarely studied in the past, such as the safety effects of climbing lanes and distance along composite descending grade. The results also showed that the CRPT model was not only able to reflect the heterogeneous effects of various factors, but also able to estimate the underlying interactions among unobserved characteristics, and therefore provide better statistical fit and offer more insights into factors contributing to freeway crashes than its model counterparts. Additionally, the results showed significant temporal instability in CRPT models across the studied time periods indicating that crash factors (including unobserved characteristics and the underlying interactions among them) and their effects on crash rates varied over time, and more attentions should be paid when interpreting crash data-analysis findings and making safety policies. The modeling technique in this study demonstrates the potential of CRPT model as an effective approach to gain new insights into safety factors, particularly when the heterogeneous effects of factors on safety are interactive. Additionally, findings from this study are also expected to assist in developing more effective countermeasures by better understanding the safety effects of factors associated with freeway design characteristics and pavement conditions.
Assuntos
Acidentes de Trânsito/estatística & dados numéricos , Ambiente Construído/provisão & distribuição , Humanos , Modelos Estatísticos , Medição de Risco , Segurança/normasRESUMO
El sedentarismo está aumentando en la Ciudad Autónoma de Buenos Aires (CABA). Es importante estudiar el ambiente construido que promueve la realización de actividad física (AF). Nuestro objetivo fue analizar la distribución del espacio verde (EV) apto para realizar AF, así como la oferta estatal de actividades deportivas gratuitas en la ciudad. Se realizó un estudio ecológico analizando y mapeando datos según fuentes e informes oficiales de CABA para 2015. Hicimos un análisis por número absoluto, superficie, densidad poblacional y valor promedio del metro cuadrado construido por comuna. Además, realizamos un análisis cualitativo según imágenes satelitales de la ciudad. La mediana de espacio verde apto para AF era de 2,6 m2/habitante (rango intercuartílico de 1,0 a 4,6). La menor cantidad estuvo en las comunas céntricas, más densamente pobladas, así como en la mayoría de las de menor valor del terreno (una de estas tenía buena cantidad de EV, pero con un ambiente construido que podría limitar la realización de AF). En cambio, en cuanto a las actividades deportivas gratuitas, a menor valor del terreno había mayor oferta. Estos resultados deben analizarse junto con condiciones ambientales y de seguridad para la planificación integral de la ciudad. (AU)
Sedentary lifestyle is increasing in Buenos Aires City (CABA). It is important to study the built environment that promotes physical activity (PA). Our objective was to analyze the distribution of the green spaces or urban open spaces (GS) suitable for PA, as well as the state offer of free sports activities in the city. We did an ecological study, analyzing and mapping data according to sources and official reports of CABA for 2015. We performed analyses by absolute number, area, population density and average value of the built squared meter for each district (comuna). In addition, we did a qualitative analysis according to satellite images of the city. The median of green space suitable for PA was 2.6 m2 / inhabitant (interquartile range 1.0 to 4.6). The smallest amount was in the central districts, more densely populated, as well as in most of the lower landvalue ones (one of these had a good amount of GS, but with a built environment that could limit the practice of PA). In contrast, regarding free sports activities, the lower the value of the land, the greater the state offer. These results must be analyzed along with environmental and safety conditions for an integral planning of the city. (AU)