We consider the kinematic model of a car which describes the rolling-without-slipping constraint of the wheels on an horizontal floor and the bound on the angle of steering of front wheels. The problem of determining shortest paths for such a vehicle is known as the Reeds and Shepp's problem. Ten years ago, a complete solution to this problem was determined on the basis of a complex reasoning grounded on the necessary conditions of Pontryagin's Maximum Principle and completed with a set of geometric arguments. In this note, we provide a simple new proof of the optimality of this construction by using a verification theorem based on Boltianskii's sufficient regularity conditions. To our knowledge, it is the first example of a regular synthesis for a nonholonomic system in a three-dimensional space.