This book presents a whole study of designing the horizontal curve, which consists of two phases. First phase contains the calculations of all curve elements of the four types of the horizontal curve and second phase contains the modeling of the ten methods of estimating the radius of the horizontal curve. This book is very important for surveying engineers and for transportation engineers. It helps them or choosing the right deign of roadways and horizontal curves with a high safety. Also this book discusses the development of computer software named as HCRET, which stands for Horizontal Curves and Radius Estimating Techniques. The program is written in Visual Basic-Version 6 language. The developed program deals with the calculation of all elements of the horizontal curve of the four types of the horizontal curves. The program also used for modeling of the ten methods of radius-estimating of horizontal curve. The program output is comprehensive and easy to understand, while the program input is user friendly and provided with many graphical objects to facilitate ease of use.