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Free flow speed is a very used transportation parameter but there are many ways to define it. In this paper "space mean speed" is used to characterize free flow conditions. The study overall objectives are, first, to determinate the time intervals that define isolated vehicle and then to develop models to estimate free-flow speed. The methodology is based on geometric features and space mean speed data collected in urban roads tangents located in Cagliari, Italy. The data were analyzed with statistical tools. It was used a multiple linear regression that allowed to obtain different models. On these models, a diagnostic analysis and residual tests was performed to assess adequacy of models (model verification phase). At last, a model validation phase was developed. The first study result shows that a vehicle is isolated when the vehicle ahead is at a time distance greater than or equal to six seconds and the following vehicle is at a time distance greater than or equal to four seconds. Based on this assumption, isolated vehicles have been identified through a survey. Three statistical models are constructed, and all these have passed the diagnostic analysis showing to be adequate to interpret the phenomenon. Nevertheless, only two are validated to predict free flow speed. Variables influencing freeflow speed are lanes width, type of median, tangent length, type of left-lateral obstacle, lateral clearance on the right side, access points and presence of crosswalk. The paper shows that even if all statistical verifications are good, it is important to validate models with a sample not used in the model construction. In fact, validation phase can ensure model replicability in different contexts. [ABSTRACT FROM AUTHOR]

Crossing red lights at intersections are serious violations and can lead to severe consequences. Official statistics show that Dubai experienced 46% of road traffic crashes due to red light crossing in the United Arab Emirates in 2016. With the lack of published studies on this important issue in Dubai, which is an important economic hub in the whole region, this study aims to investigate factors that contribute to red light violations in it. A retrospective quantitative research methodology was chosen where data on red light violations and subsequent crashes as well as road design characteristics that have the potential to affect red light crossing was collated and assessed for 16 four-leg lighted intersections with red light cameras in Dubai. Results show that red light violations rate in Dubai at intersections with red light cameras is, on the average, 0.63 per 10,000 vehicles which is considered low when compared to other cities worldwide. Results also show that there is a tendency for drivers to cross red lights more often at intersections with longer cycle duration, at wider intersections, on roads with higher speed limits and on weekends more than on weekdays. Based on the results, recommendations are given at the end to reduce red light crossing rate in Dubai further. [ABSTRACT FROM AUTHOR]

Purpose: Taking all users of the road system into account -- notably those who use non-motorized modes of transportation -- is a major challenge for urban engineers when designing roads and public spaces. And yet, although a body of knowledge exists concerning the effects of the environment on pedestrian accidentology, so far very little research has been carried out on the perception pedestrians have of the road environment (structure of buildings, vegetation, etc.) and its influence on decision-making when crossing. This exploratory research aims at studying this perception through a qualitative approach. Methods: We used the focus group method to study the perception of 20 two-way street environments with a certain level of diversity from the point of view of buildings (type, density, and heterogeneity), activities, position in relation to the city center, width of the sidewalks and type of traffic. The participants in the two focus groups were 11 regular or occasional pedestrians. Results: The verbal material obtained is analyzed in terms of perception of the environment, inferences about driver behavior (notably toward pedestrians), and influence on the pedestrian crossing behavior. Pedestrians prefer environments in which they have the "upper hand" or environments that are highly predictable. Conclusions: The results suggest a few tendencies or lines of approach concerning the design of spaces that make street crossing more comfortable for pedestrians. They also show that the focus group method is of great interest for studying the perception and interpretation of urban environments. [ABSTRACT FROM AUTHOR]

In recent years, there has been a growing need to develop and delineate algorithms that quickly provide optimized highway alignments. The matter is very complex since it is dominated by several factors and engineers have to achieve different and relevant targets (such as minimization of construction and earthwork costs, compliance with environmental and right-of-way constraints, maximization of safety and comfort for users, conformity with geometric standards). The possible solutions of this problem are clearly infinite and only modern artificial intelligence techniques can really simplify and speed up the highway design process. In this study a search algorithm, based on a Swarm Artificial Intelligence technique (Particle Swarm Optimization method), to optimize highway 3-dimensional alignments, considering also environmental constraints, is proposed. This algorithm pertains to the minimization of a particular cost function, made up of different kinds of construction costs and some penalties, related to geometric and environmental constraints (geomorphologic, hydraulic and seismic constraints) and useful to avoid and discard incorrect alignments. Some specific operators, derived from Genetic Algorithms (GAs), were also introduced in the model for improving its efficiency and correcting inappropriate solutions. To test the model efficiency, through the MatLab © software, an original script has been developed. The topography of the study area was reproduced through a particular Digital Terrain Model (DTM) representation. [ABSTRACT FROM AUTHOR]

The role of drivers is an important issue in the evaluation of new or existing roads to attain safe traffic operations. In accordance with the recent research about visual activity, in this paper, visual behaviour of a sample of drivers has been examined. Several trials has been made by means of an instrumented vehicle and a post process of image analysis. The results has permitted to propose some new synthetic indexes, correlated with the usual variables known by road engineers, that could represent a valid instrument to solve the most critical situations not yet highlighted by a collision occurrence. [ABSTRACT FROM AUTHOR]