The certificate authorizes the one-way transportation by road of cylinders that were manufactured after January 1, 1993 in accordance with a specification for cylinders set out in US DOT 49 CFR. DOT cylinders manufactured after January 1, 1993 are sometimes returned by consumers at propane refill centers, municipal waste disposal sites, or cylinder exchange sites. The TDG Regulations do not allow propane retailers to transport those cylinders back to their facility for disposal, recycling or other reclamation.