(a) The security required under this chapter shall be cash or securities permissible under state law as security for deposit of state funds and in such amount as the executive director may require but in no case in excess of the limits specified in § 15-106 in reference to the limits of a policy or bond. If at the time of the accident there is in effect a liability policy or a bond meeting the requisites of this chapter other than amount of coverage set forth in § 15-106, the executive director may consider such policy or bond in fixing the amount of security. The person depositing security shall specify in writing the person or persons on whose behalf the deposit is made and, at any time while such deposit is in the custody of the State Treasurer, the person depositing it may, upon approval of the executive director, amend in writing the specification of the person or persons on whose behalf the deposit is made to include an additional person or persons; provided a single deposit of security shall be applicable only on behalf of persons required to furnish security because of the same accident. Interest and other income upon securities deposited as herein provided shall be paid or inure to the benefit of the person making the deposit.

(b) Upon ten days’ notification of the parties concerned, the executive director may reduce or, within the limits specified in § 15-106, increase the amount of security ordered in any case if in the executive director’s discretion the amount ordered is excessive or insufficient. In case the security originally ordered has been deposited, the excess shall be returned to the depositor, notwithstanding the provisions of § 15-111. Substitution of security shall be permitted.