Drawing a curved road, or any curve in general, is difficult. If you have a pen tool that can create curves, this task might not be so difficult. But getting a curved road right when drawing it by hand or using a tablet can be a real challenge.
Draw a horizon line.
Draw a triangle with the top of the triangle touching the horizon line.
Draw lines that extend to a point further along the horizon line from exactly parallel sides of the triangle.
Use the triangles as guidelines for drawing the curved road.
Trace over the guidelines in a curving motion until you have a smooth curving road.
Going over the curving line several times can help improve the smoothness of the lines.