What is a key feature of a curve that is considered a 'spiral' in surveying?

A key feature of a spiral curve in surveying is that it allows for gradual directional changes. This type of curve serves as a transition between a straight path and a circular curve, which is essential in various applications such as road design and railroad engineering. The gradual transition minimizes sudden changes in direction, enhancing the safety and comfort of vehicles moving through the curve.

In practice, a spiral begins with a very gentle curve that gradually tightens into a sharper curve. This characteristic is particularly important in scenarios where vehicles need to maintain speed while changing direction, as it helps in managing centrifugal forces effectively.

Understanding this feature is crucial for engineers and surveyors, as it informs the design of transportation systems, ensuring they are both functional and safe for users.