Radar Detectors in Maine: Legal in a Private Car, a $250 Infraction in a Commercial Vehicle

The negative for ordinary drivers is provable rather than assumed. The Office of the Revisor of Statutes runs a full-text search over the Maine Revised Statutes, current through October 1, 2025 and the First Special Session of the 132nd Legislature, and the quoted phrases "radar detector", "radar detectors", "radar-detector", "detection device", "speed measuring" and "radar interference" all return no sections. The unquoted term "radar" returns a short and unrelated list: radar requirements for vessels operating in Casco Bay at 23 MRS §4406, 35 MRS §3321 and 35-A MRS §5108, the ferry radar chapter at Title 35 chapter 267, the speed provision at 29-A MRS §2075, and §1254 of the former Title 29, the motor vehicle title Maine replaced with Title 29-A in 1995. Maine therefore has neither a possession ban, a use ban, a mounting restriction nor a confiscation power aimed at detectors in a private car, and no fine schedule attached to one. Nothing in Title 29-A chapter 17, the equipment chapter that carries the tint rule at §1916 and the auxiliary lighting rule at §1909-B, reaches a receiver of any kind.

The commercial answer runs the opposite way, and Maine builds it in two layers. The first is 29-A MRS §555(2), which authorises the Bureau of State Police to adopt by rule, incorporated by reference, the federal regulations in 49 CFR Parts 40, 382, 383, 385, 390, 391, 392, 393, 395 and 396. The Maine Administrative Procedure Act does not apply to the adoption by reference itself, except that adopting a provision that would substantively change a state amendment, or adopting an amendment to a federal regulation, is a major substantive rule under Title 5, chapter 375, subchapter 2-A. The Bureau must file a certified copy of the rule and a published copy of the federal regulation with the Secretary of State, and file annually an updated volume of the Code of Federal Regulations.

The second layer is the rule itself. Section 3 of the Maine Motor Carrier Safety Regulation, 16-222 CMR ch. 4, adopts without state amendments "Title 49, Part 392, §§ 392.1 through 392.71 of the Code of Federal Regulations, as amended", along with Parts 40, 382, 390, 393 and 396, and separately §§ 392.80 and 392.82. The range stops exactly at 392.71, which is the federal prohibition on radar detectors in commercial motor vehicles, so Maine has adopted it rather than carved it out. Section 2 of the same chapter states that the regulation applies to any interstate or intrastate common, contract and private motor carrier that transports passengers or property in Maine, so an intrastate Maine trucking operation is inside the rule and not only interstate carriers. Section 1(A) sets the vehicle threshold: a self-propelled or towed motor vehicle used on a highway in interstate or intrastate commerce to transport passengers or property with a gross vehicle weight rating or gross combination weight rating, or an actual gross vehicle or combination weight, of 4,536 kg (10,001 pounds) or more, whichever is greater; or designed or used to carry more than eight passengers including the driver for compensation; or more than fifteen passengers including the driver without compensation; or carrying hazardous material in a placardable quantity.

Maine then went a step further than most adopting states and pulled the section number into statute. Section 558-A of Title 29-A, added by PL 2013, c. 530, §4 and amended by PL 2017, c. 165, §4, sorts motor carrier violations into crimes and traffic infractions, and subsection 2 paragraph A subparagraph (3) lists by number the federal sections that are traffic infractions rather than Class E crimes: 49 CFR §§ 392.7, 392.8, 392.9(a), 392.9(b), 392.16, 392.22, 392.24, 392.25, 392.33, 392.71, 392.80 and 392.82. The radar detector rule is therefore expressly a traffic infraction in Maine, with a mandatory $250 fine on a first violation and a mandatory $500 fine on a repeat, and not the default Class E strict liability crime that §558-A(1)(A) attaches to a violation of the subchapter or its rules generally.

Who can stop the truck is also fixed by rule. Under 16-222 CMR ch. 4, §6, only special agents of the Federal Motor Carrier Safety Administration may enforce the chapter, and §1(D) defines that term for Maine purposes as a motor carrier inspector, state police officer, municipal officer or sheriff who has satisfactorily completed a prescribed course of instruction established by the Maine State Police on the adopted federal regulations. Section 6(B) adds that a special agent approved only for driver-only aspects of the chapter must have reasonable, articulable suspicion to stop a commercial motor vehicle. The chapter's authority line runs to 29-A MRS §555, its original effective date was August 1, 1982, and the version the Secretary of State publishes carries amendments through the final major substantive adoption filed as 2015-096 on June 19, 2015.

For a driver of a private passenger car in Maine there is no violation to describe: no section of the Maine Revised Statutes prohibits owning, mounting or operating a radar detector, and there is accordingly no fine, no forfeiture and no seizure power. For a commercial motor vehicle within 16-222 CMR ch. 71 as adopted by §3 of that chapter. 71 in the traffic infraction list, the penalty is fixed rather than discretionary: §558-A(2)(B)(1) says a fine of $250 must be adjudged, and §558-A(2)(B)(2) says a fine of $500 must be adjudged for a person who violates the subsection after having previously violated it.

Motor carrier violations that are not on the §558-A(2) list fall back to §558-A(1)(A), a Class E crime that is a strict liability crime as defined in Title 17-A, section 34, subsection 4-A, and §558-A(1) caps the fine for a violation of a state rule adopting the federal regulations at $250, or $500 where the violation meets the federal definition of an out-of-service order. 3, outside a criminal investigation, is a civil violation under §558-A(4) whose fine is set with due consideration of the FMCSA uniform fine assessment program and may not exceed the amount that program provides.