Patent ID: 7010412

Claim:
In a method for designing a road, an improvement comprising calculating parameters A 1 and A 2 in an S-shaped clothoid with R 1 , R 2 , D and A 2 A 1 being known values and R 1 and R 2 being radii of two circles and A 1 and A 2 being clothoid parameters A adapted to R 1 and R 2 , respectively, and D being a shortest distance between circumferential portions of two circles, a method for calculating the S-shaped clothoid parameter comprising: a step in which an initial value of a tangential angle τ 1 of the radius R 1 is set; a step in which the tangential angle τ 1 is compared with 0, and when a result of the comparison is less than 0, since it means there is no solution, the process is stopped, and when a result of the same is greater than 0, a value of (R 1 +D+R 2 ) 2 −X M 2 is calculated, X M being a function of an unknown value τ 1 ; a step in which a value of (R 1 +D+R 2 ) 2 −X M 2 is compared with 0, and when a result of the comparison is less than 0, τ 1 is properly adjusted, and the routine goes back to the next step of setting the initial value of the tangential angle τ 1 , and when a result of the same is greater than 0, the function F(τ 1 ) is calculated and the function F′(τ 1 ) which is differentiated with τ 1 from the function F(τ 1 ) is calculated; a step in which a ratio G = F ⁡ ( τ 1 ) F ′ ⁡ ( τ 1 ) is calculated; a step in which τ 1 =τ 1 −G is calculated (τ 1 is reduced by G); and a step in which an absolute value of G is compared with a tolerance of 10 −6 , and as a result of the comparison when the absolute value of G is greater than the tolerance, the routine is fed back to the next step where the initial value of τ 1 is set, and when it is less than the tolerance, the tangential angle τ 1 is determined, and A 1 , which is a clothoid parameter A adapted to R 1 , is easily calculated using τ 1 , and A 2 , which is a clothoid parameter A adapted to R 2 , is also easily calculated using A 1 and given value A 2 A 1 .