Abstract
The paper proposes the use of the Bloss curve (also known as biparametric or bi-hyperclothoid) as a braking curve in the exit lanes of road intersections. The main international standards continue using the clohoid as the principal transitional geometric element, even though the limits of its use in driving regimes with non-uniform speeds are known. The proposal to use the Bloss curve is aimed at overcoming these limitations and opening a debate on the possible need to codify, even in the international standards, the use of more suitable alternative braking curves. In this context, a kinematic study was conducted by comparing the main parameters of the motion (lateral jerk, lateral acceleration, steering speed) between the Bloss curve and more traditional curves, such as clothoid and Generalized Cornu Spirals (GCS). Nine case studies were conducted, each case was characterized considering the type of transition curve used (clothoid, GCS and Bloss curve) and radius R of the exit curve (R = 60 m, 80 m, 100 m). The numerical values assumed by the kinematic variables along the transition curves were “locally” calculated, i.e. “pointby- point”, to take into account the non-uniform motion regime. The results obtained, limited to the cases studied, show that the Bloss curve better meets the kinematic conditions of the vehicle motion in non-uniform driving regimes. Therefore, the Bloss curve can be considered as a braking curve in the design of road intersections and be a candidate for further investigation to assess any additional benefits in terms of comfort, driving safety and visual perception of the geometric element.
Highlights
Transition curves are generally divided into two groups (La Camera, 1992): curves that can be traveled at constant speed and curves corresponding to vehicular trajectories with variable speed
In order to compare the kinematic performances of the designed transition curves, four important parameters are taken into account: lateral acceleration at, lateral jerk c, steering speed θ and rolling speed u of the roadway
R, t, u, u umax umax, m s rad/s rad/s. The conclusions of this kinematic study, which proposes the use of the Bloss curve as an alternative braking curve, can be summarized as follows
Summary
Transition curves are generally divided into two groups (La Camera, 1992): curves that can be traveled at constant speed and curves corresponding to vehicular trajectories with variable speed. The second group includes curves suitable for use at significantly variable speeds, their use is essential in certain road sections, such as exit lanes of intersections where they perform speed control function. All these curves have as theoretical reference the fundamental studies that Blaschke (1956, 1958, 1959) and Heller & Blaschke (1961) conducted on the travel dynamics of exit lanes that allowed defining the ideal line covered by a vehicle in deceleration motion. At present, the use of this curve in the exit lanes of road intersections is quite innovative
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