Search results for "Geometric design"
showing 10 items of 15 documents
Using Genetic Algorithms for Optimizing the PPC in the Highway Horizontal Alignment Design.
2016
Various studies have emphasized the interesting advantages related to the use of new transition curves for improving the geometric design of highway horizontal alignments. In a previous paper, one of the writers proposed a polynomial curve, called a polynomial parametric curve (PPC), proving its efficiency in solving several design problems characterized by a very complex geometry (egg-shaped transition, transition between reversing circular curves, semidirect and inner-loop connections, and so on). The PPC also showed considerable advantages from a dynamic perspective, as evidenced by the analysis of the main dynamic variables related to motion (as well as rate of change of radial accelera…
Estimation of Passenger Car Equivalents for Two-Lane and Turbo Roundabouts Using AIMSUN
2020
The paper addresses issues related to Passenger Car Equivalents (PCEs) at roundabouts. Compared to other road units, the curvilinear elements of roundabout geometric design may impose greater constraints on vehicular trajectories and have a significant effect on the swept envelope of heavy vehicles. Specifically, the aim of the paper is to present the methodological approach which used traffic microsimulation to estimate PCEs. Focus is made on a case study which considered the conversion of a two-lane roundabout into a basic turbo roundabout with comparable size. Empirical capacity functions for both roundabouts were derived as target values to which simulated capacities by lane were compar…
Mixed-aspect fractal surfaces
2013
In order to provide accurate tools to model original surfaces in a Computer Aided Geometric Design context, we develop a formalism based on iterated function systems. This model enables us to represent both smooth and fractal free-form curves and surfaces. But, because of the self-similarity property underlying the iterated function systems, curves and surfaces can only have homogeneous roughness. The aim of our work was to elaborate a method to build parametric shapes (curves, surfaces, ...) with a non-uniform local aspect: every point is assigned a ''geometric texture'' that evolves continuously from a smooth to a rough aspect. The principle is to blend shapes with uniform aspects to defi…
Exact, efficient, and complete arrangement computation for cubic curves
2006
AbstractThe Bentley–Ottmann sweep-line method can compute the arrangement of planar curves, provided a number of geometric primitives operating on the curves are available. We discuss the reduction of the primitives to the analysis of curves and curve pairs, and describe efficient realizations of these analyses for planar algebraic curves of degree three or less. We obtain a complete, exact, and efficient algorithm for computing arrangements of cubic curves. Special cases of cubic curves are conics as well as implicitized cubic splines and Bézier curves.The algorithm is complete in that it handles all possible degeneracies such as tangential intersections and singularities. It is exact in t…
An exact, complete and efficient implementation for computing planar maps of quadric intersection curves
2005
We present the first exact, complete and efficient implementation that computes for a given set P=p1,...,pn of quadric surfaces the planar map induced by all intersection curves p1∩ pi, 2 ≤ i ≤ n, running on the surface of p1. The vertices in this graph are the singular and x-extreme points of the curves as well as all intersection points of pairs of curves. Two vertices are connected by an edge if the underlying points are connected by a branch of one of the curves. Our work is based on and extends ideas developed in [20] and [9].Our implementation is complete in the sense that it can handle all kind of inputs including all degenerate ones where intersection curves have singularities or pa…
Complete, exact, and efficient computations with cubic curves
2004
The Bentley-Ottmann sweep-line method can be used to compute thearrangement of planar curves provided a number of geometricprimitives operating on the curves are available. We discuss themathematics of the primitives for planar algebraic curves of degreethree or less and derive efficient realizations. As a result, weobtain a complete, exact, and efficient algorithm for computingarrangements of cubic curves. Conics and cubic splines are specialcases of cubic curves. The algorithm is complete in that it handles all possibledegeneracies including singularities. It is exact in that itprovides the mathematically correct result. It is efficient in thatit can handle hundreds of curves with a quart…
Safety valuation methods at urban atypical intersections. Analysis of infrastructural scenarios
2007
The definition of decision support tools for identifying ex ante evaluation issues for road safety measures is a new challenge for policymakers and designers managing road networks with the intention of improving traffic safety for roads of their competence. This is consistent with explicit strategies on sustainability in the transport sector established at European level, considering road safety as an essential prerequisite to warrant a sustainable mobility. Based on these considerations, the need for evaluation instruments of safety conditions both for existing infrastructural schemes and for new road installations is recently arisen so that the identification of risks involved in a parti…
An overview of safety effects on pedestrians at modern roundabouts
2011
Pedestrians are important users of the transportation system, but most guidelines have given them little importance in the geometric design of roads and intersections. In these cases it can be difficult for vehicles and pedestrians to share the road safely, particularly at intersections where vehicle-pedestrian conflicts (and the risk of vehicle–pedestrian crashes) can be a frequently recurring situation even with low pedestrian volume. In a sustainable safety vision road system planning and design must include engineering choices that help to improve the sharing of road space between vehicles and pedestrians, as well as for other vulnerable users. It is known that modern roundabouts are sa…
Microsimulation-based passenger car equivalents for heavy vehicles driving turbo-roundabouts
2016
Due to its geometric design, turbo-roundabouts impose greatest constraints to the vehicular trajectories; by consequence, one can expect a more unfavourable impact of heavy vehicles on the traffic conditions than on other types of roundabouts. The present paper addresses the question of how to estimate Passenger Car Equivalents (PCEs) for heavy vehicles driving turbo-roundabouts. The microsimulation approach used revealed as a useful tool for evaluating the variation of quality of traffic in presence of mixed fleets (different percentages of heavy vehicles). Based on the output of multiple runs of several scenarios simulation, capacity functions for each entry lane of the turbo-roundabout w…
The Plateau-Bézier Problem
2003
We study the Plateau problem restricted to polynomial surfaces using techniques coming from the theory of Computer Aided Geometric Design. The results can be used to obtain polynomial approximations to minimal surfaces. The relationship between harmonic Bezier surfaces and minimal surfaces with free boundaries is shown.