The commission, in authorizing any restrictions on the speed of rail services, shall do so only upon receipt of evidence and a finding (a)that the restriction is required due to track condition, alignment, curvature of tracks, superelevation, or inadequate right-of-way protection, or any combination thereof, as the case may be, and (b)that higher speeds will have an adverse impact upon the health and safety of the public until the specified conditions are changed.