In one embodiment, a method includes the operation of segmenting a raw reference line into a plurality of reference line segments, including a first reference line segment, a second reference segment, and a third reference line segment in a sequential order, in response to receiving the raw reference line representing a route from a first location to a second location associated with an autonomous driving vehicle (ADV). The method further includes the operations of smoothing the first reference line segment and the third reference line segment using a Quadratic programming (QP) spline smoother; and smoothing the second reference line segment using a spiral smoother. Smoothed reference line segments from the plurality of reference line segments are connected to generate a smoothed reference line, which is to be used as a reference line of the route to control the ADV.