Maryland idling law: the 5-minute rule

What the law says

A motor vehicle engine may not be allowed to operate for more than 5 consecutive minutes when the vehicle is not in motion…

Md. Code, Transportation §22-402(c)(3)

Who and what it covers

The text says “a motor vehicle engine,” with no weight, fuel or commercial-use limit, so passenger cars are covered as well as trucks and buses; only Class L (historic) vehicles are excluded (§22-402(c)(5)). The limit is measured in consecutive minutes, and it appears in the same section as Maryland’s muffler and smoke rules, and its enforcement provision dates to 1971.

Exemptions

• Held motionless by traffic conditions or by mechanical difficulties the operator cannot control (§22-402(c)(3)(i))
• Operating heating, cooling or auxiliary equipment installed on the vehicle (§22-402(c)(3)(ii))
• Bringing the vehicle up to the manufacturer’s recommended operating temperature (§22-402(c)(3)(iii))
• When idling is necessary to accomplish the vehicle’s intended use (§22-402(c)(3)(iv))
• Class L (historic) vehicles are exempt from the whole subsection (§22-402(c)(5))

Penalties

The District Court of Maryland’s preset fine schedule, effective October 1, 2026, lists “Allowing m/v engine to operate for more than 5 consecutive minutes when vehicle not in motion” (TR 22-402(c)(3)) at $70.00, which includes the $7.50 Special Funds surcharge. A driver who contests the citation instead goes to court, where the general Vehicle Law ceiling applies: a misdemeanor fine “not exceeding $500” unless another penalty is provided (Transportation §27-101(b)).

Who enforces it, and how to report

Because the limit is in the Maryland Vehicle Law, it is cited like a traffic offense: the preset fine schedule is addressed to “all peace officers of the State of Maryland authorized to issue citations.” The Maryland Department of the Environment has run targeted diesel idling inspections; in a November 2021 compliance advisory for the Cheverly area it said it would partner with the Maryland Department of Transportation and the Maryland State Police to address illegal idling.

Citations under §22-402 are written by peace officers, so a vehicle idling now is a matter for the local police non-emergency line. For vehicle emissions concerns, MDE’s Air Pollution Complaints page directs people to its Air Quality Mobile Sources Program at 410-537-3270. Note the date, time, location, plate and any company name; the statute’s heating, cooling and warm-up exceptions mean a short observation may not show a violation.

Schools and school buses

Maryland has no separate statewide school-bus idling statute that we could verify. MDE’s Idle Free MD program says the Maryland State Department of Education and MDE recommend that schools create their own idling policies, which is guidance rather than law.

History

The idling limit carries a built-in phase-in: §22-402(c)(4) says that for one year from July 1, 1971 it was enforced by warning only, and after that “in the same manner as other violations of this section.”

Reporting in Maryland is unpaid. The only program that pays complainants is New York City's.