def lane_lines_directixes(lane_info):
    """
    Computes the parabola directrix for both curves.
    """

    def directrix(coefficients):
        a, b, c = coefficients
        return (b ** 2 - 4 * a * c + 1) / 4 * a

    return directrix(lane_info.left_fit), directrix(lane_info.right_fit)