B. Whenever the operating record of any person shows an accumulation of at least 18 demerit points based on convictions, or findings of not innocent in the case of a juvenile, for traffic violations committed within any 12 consecutive months, or at least 24 demerit points based on convictions, or findings of not innocent in the case of a juvenile, for traffic violations committed within any 24 consecutive months, respectively, the Commissioner shall (i) suspend the person’s license or licenses for a period of 90 days and thereafter until he attends and satisfactorily completes a driver improvement clinic or (ii) require such person to enroll in the Intelligent Speed Assistance Program established pursuant to § 46.2-507 for a period of nine months and satisfactorily complete a driver improvement clinic. The Department shall provide such driver subject to the provision of this subsection with the option, in a written notice, either to have his license suspended or to enroll in the Intelligent Speed Assistance Program. Such driver shall indicate his choice to the Department within 30 days of the receipt of such written notice. The Department shall, pursuant to clause (i), suspend the license of any driver who fails to respond to such written notice within such 30 days. At the end of a suspension period pursuant to clause (i), the person shall be placed on probation in accordance with the provisions of § 46.2-499. No restricted license issued nor enrollment in the Intelligent Speed Assistance Program required pursuant to this section shall permit any person to operate a commercial motor vehicle, as that term is defined in § 46.2-341.4.