This paper deals with the analysis of the main variables involved in the visual activity of a driver of motor vehicles, in order to identify the most important quantities and implement, therefore, appropriate corrective actions to the achievement of road safety. The first step in this research was to survey a number of variables within the road environment and processing this data base with clustering techniques in order to extract useful information for purpose. In this case, a mixture of procedures based on Fuzzy Logic (FL) and Artificial Neural Network (ANN) were applied not only to extract knowledge not known a priori but, above all, to define the membership functions and rules of the fuzzy model without recourse to the skills of the analyst, not always so objective. This procedure, applied to a rural road open to traffic, showed a good performance in predicting the user's visual behavior and, especially, in identifying the most influential variables. This aspect may allow the agency to direct the maintenance operations so that to facilitate understanding of the information contained within the road environment, thus improving safety.
The use of transition curves in the road design is a solution to make the gradual evolution of curvature and, at the same time, to improve the comfort level of drivers and provide a good visual perception of the curve. Clothoid is the most widely used transition curve in road design so far, because it ensures the continuity of the curvature with the other geometric elements of the alignment.
However, several researches allow the use of polynomial functions as an alternative to the clothoid. Such use is permitted in accordance with the verification of allowable vehicle–road dynamics.
Polynomial solutions of transition curves can be a valuable alternative for the traditional solutions (first transition curve, circular arc, second transition curve).
A fifth‐degree polynomial parametric curve (PPC‐curve) for the design of highway alignment is proposed in this article. An analysis of the theoretical aspects to solve more complex geometrical problems recurring in practical highway geometric design is carried out. With regard to this problem, a shape parameter giving flexibility to the polynomial solution in relation to project needs has also been introduced.
To implement the procedure, an original computer program has been developed. Numerical applications have been performed for comparison with the traditional solutions.
The current international road standards, in order to give organization and safety, promote the classification of roads according to their technical and functional characteristics beyond their administrative membership, but the procedures are yet strongly based on the expertise's judgment. In fact, although this activity has a great importance for the consequences that produces in terms of responsibility and allocation of economic resources, it is solely based on the quantification of some variables without specifying methods or analytical procedures. In this paper, after an instrumental survey of the road environment, we applied data mining techniques that consider the 'vagueness' of the analysed scenario. The type of algorithms used, therefore, permits to quantify a degree of membership (among 0 and 1) of a road to the groupings provided and to prepare any corrective action in order to direct the final result towards a specific class with greater precision. In addition, this method is very flexible and willing to contain new variables or observations at different times with great easiness. Moreover, the geographical location of the individual observations, as it was done also in this research, can be transferred to a GIS system, with a positive impact on maintenance programs.
The term 'Context Sensitive Solutions' was adopted by the Federal Highway Administration in 1997 and is a synonym of flexibility that allows the designer to balance the safety, mobility and preservation of environmental resources. When the optimal use of design criteria produces an unacceptable solution, the correct application of design value outside the current guidelines with a particular attention to safety and legal risk is needed. In this case, a feasible alternative meets the purpose of design and is considered constructible and maintainable within social, economic and environmental constraints. Unlike in many other countries, road standards in Italy do not permit to work out a simple solution to the problem of flexibility. Speciflcally, one of the most debated subjects, concerning the items of the Italian Ministerial Decree (MD) 5/11/2001 confer with a designer the possibility of deviating from prescriptive obligations on condition to suggest some appropriate safety analysis. However, it does not indicate any methodology to objectively quantify removal eflect from the reference values established by the rule. At this purpose, the paper suggests an analytical instrument for controlling design values outside the current guidelines applying a methodology based on interval analysis, a technique generally used for managing uncertain variables. The procedure applied to designing a planimetric curve has identified the most significant variables and produced some range in which they may be retained acceptable, though outside the limits of the geometric standard.
The proposed research addresses the problem of predicting driver's visual behavior. Notably, this issue is of great importance for road safety because it provides information about the true perception of the road environment. This need is particularly felt when the real situation is so complex that it cannot be represented by simple analytical audits contained in the road international standard. Therefore, with the help of an instrumented vehicle, the authors conducted some trials to identify relevant data useful to recognize the road environment as perceived by drivers. Based on this data, the authors prepared a linear model that, properly calibrated, would enable them to predict the drivers' visual strategy. The results were encouraging, because a model so simple in structure as well as in the number of variables involved could control a very complex phenomenon, such as that of visual perception. The proposed methodology can be applied as a further control in the design of new roads and in the maintenance of existing ones and, in particular, in the analysis of special scenarios (e.g., unusual conditions of weather or traffic) that are not represented by ordinary audits contained in the road standards.
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