Closest Point on Spline (+Offset) to some World Position

[_Aka_]

Hi,
This should answer your question:

Code:

Vector3 P;
float carTf = yourSpline.GetNearestPointTF(carTransform.position, out P);
Quaternion splineOrientation = yourSpline.GetOrientationFast(carTf);
//the projection is to handle possible scenarios where the car is not on the road
Vector3 carProjectionToRoadCenter = Vector3.ProjectOnPlane((carTransform.position - P), splineOrientation * Vector3.up);
float lanePosition = Vector3.Dot(carProjectionToRoadCenter, splineOrientation * Vector3.right);