This paper presents the findings of a comparative road safety assessment between an existing two-lane roundabout and proposed basic turboroundabout, both designed for the same intersection, to determine which one is safer, based on traffic conflicts and surrogate safety measures. We performed microsimulation models in VISSIM to replicate the fieldobserved traffic operation, and the SSAM to determinate six surrogate measures. We validated the consistency of values obtained by several statistical analyzes. The number of conflicts was 72% lower at the turboroundabout. Through a complete-linkage clustering analysis and Euclidean distances of the surrogate measures, we found that traffic conflicts at the turbo-roundabout tend to cluster in a group, whereas conflicts at the roundabout are scattered, suggesting better organization of traffic flows at the turbo-roundabout. Three-dimensional graphical analysis of clusters and its centroids allowed verifying that surrogate measures point out a safer operation at the turbo-roundabout, even though it presented higher operating speeds. Reducing the dimensionality by principal components analysis, the cumulative variance for the first two components (87.72%) allowed observing results on a two-dimensional graph and their clusters. To endorse conflicts classification, resulting of clusters, we used discriminant analysis. Results validate the methodology and the safety benefits of the turbo-roundabout.

Public transport priority systems such as Bus Rapid Transit (BRT) and Buses with High Level of Service (BHLS) are top-rated solutions to mobility in low-income and middle-income cities. There is scientific agreement that the safety performance level of these systems depends on their functional, operational, and infrastructure characteristics. However, there needs to be more evidence on how the different characteristics of bus corridors might influence safety. This paper aims to shed some light on this area by structuring a multivariate negative binomial model comparing crash risk on arterial roads, BRT, and BHLS corridors in Bogotá, Colombia. The analyzed infrastructure includes 712.1 km of arterial roads with standard bus service, 194.1 km of BRT network, and 135.6 km of BHLS network. The study considered crashes from 2015 to 2018 –fatalities, injuries, and property damage only– and 30 operational and infrastructure variables grouped into six classes –exposure, road design, infrastructure, public means of transport, and land use. A multicriteria process was applied for model selection, including the structure and predictive power based on [i] Akaike information criteria, [ii] K-fold cross-validation, and [iii] model parsimony. Relevant findings suggest that in terms of observed and expected accident rates and their relationship with the magnitude of exposure –logarithm of average annual traffic volumes at the peak hour (LOG_AAPHT) and the percentage of motorcycles, cars, buses, and trucks– the greatest risk of fatalities, injuries, and property damage occurs in the BHLS network. BRT network provides lower crash rates in less severe collisions while increasing injuries and fatalities. When comparing the BHLS network and the standard design of arterial roads, BHLS infrastructure, despite increasing mobility benefits, provides the lowest safety performance among the three analyzed networks. Individual factors of the study could also contribute to designing safer roads related to signalized intersection density and curvature. These findings support the unique characteristics and traffic dynamics present in the context of Bogotá that could inform and guide decisions of corresponding authorities in other highly dense urban areas from developing countries.

Preferential bus lanes are a widely use strategy to promote travelers to use public transport instead of private cars. Considering its relevance in the urban transportation planning and operation, it is crucial to evaluate them in terms of the operation and safety externality. We performed a road safety assessment in preferential public transport lanes with complex driving environment using a preventive approach on the 7 th Avenue, in Bogota (Colombia), between 39 th Street and 45 th Street. A detailed study of traffic conflicts was carried out under the guidelines of the Swedish technique, which uses the Time to accident and Conflicting speed to establish the severity of a conflict. A traffic conflict is defined as an incident where, if two road users on collision course maintain their speed and trajectory constant, the crash between them will be imminent. With the field information, we calibrated a VISSIM microsimulation model that correctly replicates its traffic operation. Using the SSAM tool, we validated the base model to identify the simulated traffic conflicts in VISSIM and compared them with the observed conflicts. Under the calibrated environment, we developed and assessed three different scenarios of countermeasures to reduce the number of conflicts observed. As a result, we found that the safest scenario is the one established in the regulations that normalize the operation in preferential lanes, currently not obeyed by most users. Based on our results, we recommend an adjustment in the normative measures, including regulating the stopping time and stopping zones of private vehicles and taxis.

Este documento presenta un modelo físico novedoso que permite medir la conductividad hidráulica en materiales granulares saturados. Una innovación en la ubicación de los piezómetros del dispositivo permite que este se use para evaluar la permeabilidad de los suelos estratificados tanto para flujos paralelos como perpendiculares. La construcción de la sección cuadrada del modelo facilita la compactación del suelo. La metodología de diseño tuvo en cuenta aspectos de construcción, calibración e implementación. Se midieron los coeficientes de permeabilidad en direcciones paralelas y perpendiculares a la estratificación del suelo. Además, se realizó la prueba-t de Student para la relación de los resultados experimentales y correlaciones numéricas existentes. El análisis de resultados muestra que el modelo físico puede replicar el fenómeno de filtración de agua a través de suelos granulares estratificados como sucede en campo. Por otra parte, se encontró que es posible validar el procedimiento de calibración experimental mediante técnicas estadísticas.

Fluctuation of groundwater level induces changes in pore-water pressure of soil. However, this variation is not considered for underground constructions. This article explores the application of a statistical method to evaluate the groundwater level variation in geotechnical designs. The methodology included: (i) data collection, (ii) statistic formulation, and (iii) statistic data analysis. We collected information from the technical studies of the project “Metro de Bogotá”, and selected four boreholes spanning 160 m, approximately, where the 1° de Mayo metro station will be built, in the south of the city. We used groundwater level readings reported by different piezometers for 30 days and data variance was assessed using a multivariate statistical method: analysis of repeated measures profiles. Results present a procedure to estimate the groundwater level fluctuation during a short monitoring period. We concluded that the analysis of repeated measures profiles allows estimating the groundwater level variation under a significance level 1-a.