Road Geometry Standards (Layout)
Introduction
Geometric road design is the civil engineering technique that consists of placing the layout of a road or street on the ground. The conditions for locating a road on the surface are many, including the topography of the terrain, geology, the environment, hydrology or social and urban factors.[1] The first step in designing a road is a feasibility study[2] that determines the corridor where the road layout could be located. Generally, several corridors are studied and the environmental, economic or social cost of road construction is estimated. Once a corridor has been chosen, the exact layout is determined, minimizing the cost and estimating the total cost in the construction project, especially that which will involve the volume of earth displaced and the necessary pavement.
Road classification
Roads are classified based on the number of carriageways, the dimension of the carriageway lane or the dimension of the shoulder. The larger the dimensions of the road, the more traffic it can support and the more demanding the layout parameters will be, that is, it will be necessary to make larger curve radii, more extended vertical agreements or steeper superelevations. By increasing these parameters the road will conform less to the terrain, which makes the road more expensive.
The most important data for the design is the design speed, which is the maximum speed to circulate comfortably and safely.
Introduction to the geometry of a road
Contenido
La geometría de una carretera queda determinada en las 3 direcciones del espacio y queda fijada mediante 3 planos:.
Stopping distance
A driver must be able to see a sufficient distance ahead to be able to brake if encountering an obstacle. The stopping distance of a vehicle is equal to[3][4].
Being the speed in km/h, the perception and reaction time (2 s), the coefficient of longitudinal wheel-pavement friction, the inclination of the grade in both times one and the stopping distance in meters. In the geometric design of roads, it must be ensured at all points on the route that it sees this number of meters in front of it, which implies clearing the terrain, smoothing changes in grade and taking care of visibility on curves.