What does the term "point of tangency" (PT) refer to in roadway design?

In roadway design, the term "point of tangency" refers specifically to the point at which a curve ends and the roadway transitions back to a straight alignment. This point is crucial for understanding the geometry of road design, as it determines how vehicles will move out of the curve and into a straight segment, affecting factors such as speed, visibility, and safety.

When a road curves, it requires precise calculations to ensure that vehicles can smoothly navigate the transition at the point of tangency without abrupt changes in direction. The design must take into account factors such as the radius of the curve and the desired speed of travel. Recognizing the point of tangency is essential for properly designing curves in various types of roadways to maintain safe and efficient travel. This is why the identification of the end of the curve aligns perfectly with the definition of point of tangency.