Vehicles abandoned in or upon vehicular crossings may be sold or disposed of by the Triborough Bridge and Tunnel Authority in such manner as it may deem best. Vehicles shall be deemed to have been abandoned if found unattended in or upon vehicular crossings. However, vehicles left in such places as may be designated by the Triborough Bridge and Tunnel Authority as parking areas shall not be deemed to have been abandoned unless such vehicles are permitted to remain in such areas for a period in excess of 18 hours.