If R is the radius of the main curve, θ is the angle of deflection, S is the shift and L is the length of the transition curve, then the total tangent length of the curve is:
1
(R + S) tan θ/2 – L/2
2
(R + S) tan θ/2 + L/2
3
(R - S) tan θ/2 – L/2
4
(R - S) tan θ/2 + L/2