Types of Horizontal Curves

A curve may be simple, compound, reverse, or spiral (figure l). Compound and reverse curves are treated as a combination of two or more simple curves, whereas the spiral curve is based on a varying radius.

Simple
The simple curve is an arc of a circle. It is the most commonly used. The radius of the circle determines the “sharpness” or “flatness” of the curve. The larger the radius, the “flatter” the curve.

Compound
Surveyors often have to use a compound curve because of the terrain. This curve normally consists of two simple curves curving in the same direction and joined together.

Reverse
A reverse curve consists of two simple curves joined together but curving in opposite directions. For safety reasons, the surveyor should not use this curve unless absolutely necessary.

Spiral
The spiral is a curve with varying radius used on railroads and somemodern highways. It provides a transition from the tangent to a simple curve or between simple curves in a compound curve.