I Go Cars logo — a patrol car with a red and blue lightbarI Go CarsPolice & government vehicles

Traffic enforcement

Radar detectors in commercial vehicles

Federal rules bar radar and laser detectors in every commercial motor vehicle of 10,001 lb or more, in all 50 states.

By I Go Cars ·

The rule: no radar detectors in commercial motor vehicles

A commercial motor vehicle (CMV), for federal motor carrier safety purposes, is a vehicle used in interstate commerce with a gross vehicle weight rating, gross combination weight rating or actual weight of 10,001 lb or more, along with certain passenger-carrying and hazardous-materials vehicles. Radar detectors are banned in every CMV nationwide. The ban is 49 CFR 392.71, a rule of the Federal Motor Carrier Safety Administration (FMCSA), and it applies in all 50 states, including the 49 where a radar detector is legal in a private car.

The rule has three parts. No driver may use a radar detector in a CMV. No driver may operate a CMV that is equipped with one. No motor carrier (the company that operates the vehicle and employs or contracts the driver) may require or permit a driver to do either. The second clause matters most in practice: the vehicle does not have to be moving with the detector switched on for a violation to occur; operating a truck equipped with one is enough.

This page describes what the federal regulations and state statutes say, as read in October 2026. It is not legal advice, and penalty amounts in particular change with inflation adjustments, so the current text should be checked before anyone relies on a figure.

Which vehicles count as a CMV

The definition in 49 CFR 390.5 sets the weight line at 10,001 lb (4,536 kg). The measure is the gross vehicle weight rating (GVWR, the maximum loaded weight the manufacturer assigns to the vehicle), the gross combination weight rating (GCWR, the same figure for a vehicle plus its trailer) or the vehicle's actual weight. The definition also reaches vehicles designed to carry passengers above set thresholds and vehicles hauling hazardous materials.

The 10,001 lb threshold is the point most drivers get wrong. The federal detector ban is not limited to tractor-trailers or to the heavier class of trucks; many box trucks and pickups pulling trailers in interstate commerce cross the line. A heavy-duty pickup towing a loaded trailer for a business across a state line can be a CMV for this rule.

The federal definition applies to interstate commerce. Many states adopt the federal motor carrier safety regulations, including 392.71, for carriers operating only within the state, but that adoption was not verified state by state for this page.

What counts as a radar detector under federal rules

The same section, 49 CFR 390.5, defines a radar detector broadly: any device or mechanism that detects radio microwaves, laser beams or any other future speed-measurement technology used by law enforcement. Laser-only detectors are therefore covered, and a combined radar and laser unit is covered twice over. The definition is written to cover technology that did not exist when the rule was adopted.

The definition has one exception. A device is not treated as a radar detector for this rule if it is located outside the driver's compartment and is completely inaccessible to the driver. An unplugged detector in the glove box, the sleeper berth or a door pocket does not meet that test, because it remains inside the compartment and within the driver's reach.

Products sold as radar jammers raise a separate question. FMCSA guidance says devices that only reflect incoming energy passively, or that transmit steadily on a police radar frequency, are not radar detectors under the rule. Devices that detect and isolate the incoming signal and then transmit on the same frequency do qualify as radar detectors, so 392.71 bans them in CMVs. Radar jammers are also illegal for every driver under Federal Communications Commission (FCC) rules. The rule text is on eCFR (49 CFR 390.5).

Penalties: federal maximums, CSA scores and state fines

Federal civil penalties for violations of the motor carrier safety regulations are set in 49 CFR Part 386, Appendix B. As read on eCFR on Oct. 29, 2026, a driver who violates a non-recordkeeping requirement in Parts 390 through 399 is subject to a civil penalty of up to $4,812, and a person or entity, such as a motor carrier, is subject to up to $19,246 for each violation. Appendix B does not name 392.71 specifically; these maximums apply because 392.71 is a non-recordkeeping rule in Part 392. The amounts are ceilings, not typical assessments, and they are adjusted for inflation periodically.

The fine is not the only cost. FMCSA's Safety Measurement System, the public side of its Compliance, Safety, Accountability (CSA) program, records violation code 392.71(a), "Using or equipping a CMV with radar detector," in the Unsafe Driving category with a severity weight of 5. For comparison, speeding 6 to 10 mph over the limit carries a weight of 4, speeding 15 mph or more over carries 10, and a seat belt violation carries 7. A detector violation therefore counts against a carrier's safety measurement in the same category as speeding.

No source found lists 392.71 among the out-of-service criteria that take a truck or driver off the road on the spot, and the FMCSA example data show no out-of-service violations for it. Whether it is ever treated as out-of-service under the Commercial Vehicle Safety Alliance criteria was not confirmed, because that document is not public.

State rules: New York, Illinois, Virginia and D.C.

Two states add their own detector rules for heavy and commercial vehicles, with lower fines and different thresholds from the federal rule.

  • New York. Vehicle and Traffic Law § 397-a bars a radar detector or laser detector in any motor vehicle with a GVWR over 18,000 lb, and in any commercial vehicle with a GVWR over 10,000 lb. A detector connected to a power source and in operable condition is presumed to be in use, a presumption the driver may rebut. The offense is a traffic infraction with a fine of $25 to $100, and the section authorizes no seizure. Because the 18,000 lb clause reaches any motor vehicle, it applies to heavy vehicles that are not used commercially.
  • Illinois. 625 ILCS 5/12-714 bars operating, or being in actual physical control of, a commercial motor vehicle equipped with a radar detector. A detector in a locked opaque box, or outside the passenger compartment and not operating, is not a violation. The offense is a petty offense with minimum fines of $50 for a first offense and $100 after that; the device is seized on a repeat conviction, and police may not stop a vehicle solely for this violation.
  • Virginia and Washington, D.C. Both ban radar detectors in all vehicles, trucks included: Virginia under Va. Code § 46.2-1079 and the District under 18 DCMR § 736.

The state fines are modest next to the federal maximums. Whether other states have additional truck-specific detector statutes was not compiled for this page. New York's statute is published by the New York State Senate.

Can police tell a truck has a radar detector?

A radar detector can, in principle, be detected itself. A radar detector is a receiver, and its internal local oscillator (the circuit that generates a reference signal to tune the receiver) leaks a weak signal. The FCC found in 2002 that radar detectors radiate in the 11.7 to 12.2 GHz band and set emission limits there, effective Aug. 28, 2002, for detectors made or imported after that date. In the same proceeding the FCC noted that manufacturers had changed their oscillators to enhance detection of police radar while "making it more difficult for police to detect the presence of radar detectors in vehicles."

Equipment built to sense those emissions is called a radar detector detector (RDD). No U.S. agency document describing RDD use in commercial vehicle enforcement was found. The only U.S. account located is trade press: in January 2002, Heavy Duty Trucking reported that Texas Department of Public Safety license and weight troopers had been equipped with devices to detect trucks using radar detectors, with FMCSA grant money paying for 101 units and 43 more planned. That report is more than two decades old, names no device and is not an agency record, so it should be read as historical. The only government statement found on RDDs is from outside the U.S.: a 2007 answer from Queensland's Minister for Police, in Australia, said police there used RDDs across the state. Current U.S. practice is unverified.

Common misconceptions

  • "Only big rigs are covered." The federal line is 10,001 lb GVWR or GCWR under 49 CFR 390.5, which includes many box trucks and pickups with trailers in interstate commerce.
  • "A laser-only detector is allowed." The federal definition covers devices that detect laser beams, and New York's § 397-a names laser detectors expressly.
  • "Unplugged in the cab is fine." The federal exception requires the device to be outside the driver's compartment and completely inaccessible. New York presumes use when a detector is powered and operable.
  • "It is only the driver's problem." 392.71 also bars the motor carrier from requiring or permitting detector use, and the violation counts in the carrier's CSA Unsafe Driving measurement.
  • "It puts the truck out of service." No source found lists 392.71 in the out-of-service criteria; FMCSA records it as an Unsafe Driving violation with severity weight 5.

Frequently asked questions

Are radar detectors legal in commercial trucks?

No. 49 CFR 392.71 bars any driver from using a radar detector in a commercial motor vehicle or operating a CMV equipped with one, and bars carriers from permitting it. Under 49 CFR 390.5 a CMV includes interstate vehicles with a GVWR or GCWR of 10,001 lb or more. The ban applies in all 50 states, regardless of whether detectors are legal in private cars there.

What is the fine for a radar detector in a CMV?

The federal maximum civil penalty is $4,812 for a driver and $19,246 per violation for a carrier, under 49 CFR Part 386, Appendix B, as read in October 2026. Those are ceilings that are adjusted for inflation, not typical amounts. States add their own fines: New York charges $25 to $100, and Illinois sets minimums of $50 and $100.

Can police detect a radar detector in a truck?

It is possible in principle. Radar detectors leak a weak signal from their local oscillator, which the FCC found in 2002 falls in the 11.7 to 12.2 GHz band, and devices called radar detector detectors are built to sense it. A 2002 trade-press report said Texas troopers used them for truck enforcement. No current U.S. agency document on their use was found.

Does a laser detector count as a radar detector for truck drivers?

Yes. The federal definition in 49 CFR 390.5 covers any device that detects radio microwaves, laser beams or future speed-measurement technology used by police. New York's VTL § 397-a also names laser detectors expressly for vehicles over 18,000 lb GVWR and commercial vehicles over 10,000 lb. A laser-only unit gives a CMV driver no exemption from 392.71.

Does a radar detector violation affect CSA scores?

Yes. FMCSA's Safety Measurement System records violation 392.71(a), using or equipping a CMV with a radar detector, in the Unsafe Driving category with a severity weight of 5. That is slightly above speeding 6 to 10 mph over, weighted 4, and below speeding 15 mph or more over, weighted 10. The violation counts against the carrier's safety measurement as well as the driver.

Is an unplugged radar detector in the cab legal?

No, under federal rules. 49 CFR 390.5 exempts a device only if it is outside the driver's compartment and completely inaccessible to the driver, so an unplugged unit in the cab or sleeper is still covered. Illinois law separately allows a detector in a locked opaque box, but that state exception does not override the federal rule for interstate CMVs.

Sources

Top