Spiral curves

Spiral curves

Spiral curves were originally designed for the Railroads to smooth the transition from a tangent line into simple curves. They helped to minimize the wear and tear on the tracks. Spiral curves were implemented at a later date on highways to provide a smooth transition from the tangent line into simple curves. The highway engineers later determined that most drivers will naturally make that spiral transition with the vehicle; therefore, spiral curves are only used on highways in special cases today.
Because they were used in the past and in special cases today, we need to know how to calculate them.
From the surveyor’s perspective, the design of spiral curves has already been determined by the engineer and will be documented on existing R/W and As-built plans. All we have to do isuse the information shown on these plans to fit the spiral curve within our surveyed alignment.