A special license required to operate certain large, heavy, or hazardous vehicles for work.

"Special" means it comes with stricter testing and medical rules than an ordinary driver's license. A driver usually must pass knowledge and road exams, meet federal medical standards, and carry any needed endorsements for tank vehicles, passenger vehicles, school buses, or hazardous materials. "Large, heavy, or hazardous" points to the kinds of vehicles covered, such as tractor-trailers, buses, and trucks carrying certain loads. Under the federal Commercial Motor Vehicle Safety Act of 1986, states issue CDLs using national standards. In Connecticut, the DMV handles CDL licensing, and crash investigations involving commercial vehicles may also draw attention from agencies such as Connecticut State Police Troop G on the Merritt Parkway corridor.

For an injury claim, a CDL can become key evidence. It may show whether the driver was properly trained, medically qualified, and authorized to drive that vehicle with that cargo. Missing endorsements, an expired medical certificate, or a suspended CDL can support arguments about negligence, negligent hiring, or negligent retention.

A CDL also matters because commercial drivers and motor carriers are held to safety rules that do not apply to ordinary motorists. If a crash involves a fleet truck serving an industrial employer in East Hartford or another work route, lawyers often examine the driver qualification file, training records, and any CDL restrictions to see whether a safety violation helped cause the collision.