Maryland Truck Emissions & Clean-Truck Rules

How Maryland handles truck emissions

Maryland tests your smoke at the roadside. Any diesel over 10,000 lb GVWR or GCWR on a Maryland highway can be stopped by State Police or MdTA Police and given an opacity test, and out-of-state plates are not exempt (Md. Transportation Article 23-401 to 23-404). The limit is 40 percent opacity for engines 1991 and newer. Fail and you get a repair order: 30 days to repair and retest on Maryland plates, 15 days to certify on out-of-state plates, then a fine up to $1,000. Maryland's Advanced Clean Trucks rule (COMAR 26.11.43) is a sales mandate on manufacturers and costs you nothing at the roadside. Keep the DPF/DEF working; a delete risks about $45,000 per engine.

What applies to you

• Program: Clean Truck Check
• State rule: 40 percent opacity is your limit in Maryland on any engine 1991 or newer, 55 percent for 1974 to 1990, 70 percent for 1973 and older (COMAR 11.21.02.06). Maryland runs a statewide roadside diesel smoke program covering every diesel over 10,000 lb GVWR or GCWR traveling on its highways, out-of-state plates included (Md. Transportation Article 23-401 to 23-404; COMAR 11.21.02). Maryland State Police and MdTA Police can require any heavy-duty diesel to submit to a smoke opacity test during a weighing or motor carrier safety inspection, or at any location or time when an officer has reasonable cause. Maryland also adopted Advanced Clean Trucks (COMAR 26.11.43, Clean Trucks Act of 2023), a zero-emission sales mandate on manufacturers from model year 2027 that binds no driver, and Governor Moore's April 2025 executive order gave MDE enforcement discretion and waived penalties for model year 2027 shortfalls.
• Penalty: Up to $1,000 if you do not clear a Maryland smoke opacity violation (Md. Transportation Article 23-404). A Maryland-plated truck gets a Safety Equipment Repair Order and must be repaired and retested within 30 days or the registration is suspended. An out-of-state truck gets a Maryland Driver/Vehicle Inspection Report and the owner has 15 days to return it certified to the Maryland State Police; run more than 30 days delinquent and State Police notify the Federal Highway Administration of a 49 CFR 392.2 violation. ACT penalties fall on manufacturers, not drivers. Federal Clean Air Act tampering penalties still apply: about $45,000 per tampered engine and about $4,500 per defeat device.
• DPF / DEF: Federal EPA equipment nationwide, never delete or tamper with it

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