Roads, or streets, are paths designated and designed to provide for various modes of transportation that connect different places. Often times paved or leveled out in someway to promote their functionality, roads take up all different types of layouts, be it a freeway, local road or surface street, interstate highway, and so on. Depending on the context and function that a road is meant to serve, its layout will range in its number of lanes and lane width along with the presence of a paved sidewalk, bike lanes or other cycling infrastructure, pedestrian crossings, and the occurrence of road junctions.
Curves are important in road design as they provide transitions between straight roadways for gradual turns. In designing a road, following land formations through use of curves is cost effective and less demanding of construction. Minimizing steepness of hills for vehicles, especially trucks, is also an important reason for implementing curves in road design.
Geometric design focuses on producing efficient, safe, economic, and environmentally conscious roads that are influenced by the vehicles, the drivers, and traffic conditions. Another objective of geometric design is to construct roads that provide for a sense of community and opportunity for the public. Alignments (horizontal and vertical), cross-sections, and profiles are three aspects of geometric design that, in combination, determine the layout for roadway design.
The K-value is representative of the horizontal distance at which a one percent grade change occurs along a vertical curve. There is a target minimum curve length as this K-value expresses abruptness of the grade change. The curve must be long enough so that the driver of a vehicle can see an obstruction, an oncoming vehicle, and prevent excessive forces on passengers traversing along the curve at the designated speed.
