Could North Carolina pass a law or rule allowing window tint as dark as 35% light transmittance on passenger car windows when federal safety standards require 70%?
Plain-English summary
DMV Commissioner William Hiatt asked AG Lacy Thornburg whether NC could allow window tint dark enough to limit light transmittance to 35% on the windows of a passenger car. The federal Motor Vehicle Safety Standard for glazing materials (Standard No. 205) required 70% light transmittance through the windshield and the windows immediately to the right and left of the driver, plus the rearmost windows if used for driving visibility. So the practical question was whether a state law setting 35% could survive federal preemption.
The AG said no. The Motor Vehicle Safety Act expressly preempts conflicting state safety standards. 15 U.S.C. § 1392(d) provides that when a federal motor vehicle safety standard is in effect, "no State or political subdivision of a State shall have any authority either to establish, or to continue in effect" any safety standard "applicable to the same aspect of performance" that "is not identical to the Federal standard." Window light transmittance is exactly such an aspect of performance. A NC rule setting 35% would directly conflict with the 70% federal floor, and would therefore be preempted.
The AG also pointed to the separate federal prohibition in 15 U.S.C. § 1397(a)(2)(A), which forbids any manufacturer, distributor, dealer, or motor vehicle repair business from "knowingly render[ing] inoperative" any element of design installed to comply with a federal safety standard. A tint shop that applies film bringing total light transmittance below 70% to a window that originally complied is, on the federal reading, rendering Standard No. 205 inoperative. Each such installation can carry a federal civil penalty of up to $1,000.
The narrow exception in § 1392(d) lets a state impose a higher standard, but only as a procurement spec for vehicles the state itself buys, not as a rule of general application. A 35% rule for the public is the opposite direction: less stringent than federal, applied generally, so squarely preempted.
The takeaway for NC: tint rules can match or exceed the federal floor, but they cannot lower it. Any state effort to allow darker tint on safety-glazed windows runs into both the express preemption clause and the federal "render inoperative" rule that captures the installers and dealers downstream.
Currency note
This opinion was issued in 1987. Subsequent statutory amendments, court decisions, or later AG opinions may have changed the analysis. Treat this page as historical context, not current legal advice. Verify current law before relying on any specific rule, deadline, or remedy mentioned here. The Motor Vehicle Safety Act has been recodified at 49 U.S.C. Chapter 301, with the preemption provision now at 49 U.S.C. § 30103 and the prohibitions on manufacturers, dealers, and repair businesses at 49 U.S.C. § 30122. Standard No. 205 still requires 70% light transmittance for windows requisite for driving visibility, but the precise text and the exceptions for medical waivers and aftermarket film have evolved. NC's own window-tint statute (now codified in Chapter 20) has also gone through several rounds of amendment that allow somewhat darker tint on rear-side windows and rear windshields than on front-side windows, paralleling the federal "driving visibility" distinction. Anyone checking the current law should pull the current G.S. 20-127 (and its subsections) and the current 49 C.F.R. § 571.205.
Background and statutory framework
The Motor Vehicle Safety Act was enacted in 1966 to give the National Highway Traffic Safety Administration (NHTSA) authority to issue uniform safety standards for new motor vehicles and motor vehicle equipment. The Act defined "motor vehicle equipment" broadly to include not only original components but also accessories and add-ons made or sold for use with a motor vehicle. Window tint film is both a manufactured product sold for "improvement" of an existing motor vehicle component (the glass) and an item "intended for use exclusively to safeguard motor vehicles, drivers, passengers, and other highway users from risk of accident, injury, or death." Both categories pull it under NHTSA's authority.
Standard No. 205 ("Glazing Material") incorporates the American National Standard "Safety Code for Safety Glazing Materials for Glazing Motor Vehicles Operating on Land Highways" (ANSI Z26). The standard imposes specific light-transmittance and abrasion-resistance requirements. For passenger vehicles, all windows must transmit at least 70% of visible light. For multipurpose passenger vehicles (the regulatory ancestor of the modern SUV), motor homes, and trucks, the 70% requirement applies to the windshield, the windows to the immediate right and left of the driver, and the rearmost windows when those are used for driving visibility. Notice the structural rule: the 70% floor is keyed to whether the window is needed for the driver to see out, not to whether it is in the front or back of the vehicle.
The federal preemption clause, 15 U.S.C. § 1392(d), is an express clause. It does not just imply preemption from the field; it specifically forbids any state safety standard "applicable to the same aspect of performance" that "is not identical to the Federal standard." Window-glass light transmittance is one aspect of performance, and the federal standard specifies it numerically. A state cannot pick a different number for the same aspect. The exception is narrow: a state can require a higher standard for vehicles the state purchases for its own use, but cannot generally regulate private vehicles to a different number.
The AG cited California Federal S. & L. Assn. v. Guerra for the proposition that "Congress may preempt State law by so stating in express terms." Guerra is actually a 1987 Title VII preemption case, not a motor-vehicle case, but the cited proposition is generic preemption doctrine and applies the same way here. Express preemption clauses do the work that implied conflict preemption would otherwise require.
The "render inoperative" provision (15 U.S.C. § 1397, now codified at 49 U.S.C. § 30122) catches the downstream actors. Even if a state's tint rule is not enforced against the driver, the federal rule reaches the tint shop, dealer, or repair business that installs film bringing total light transmittance below the federal floor. Each installation can be a separate violation. The civil-penalty exposure is what gives the federal floor real bite at the consumer-product layer, because the typical tint customer is buying the install from a regulated business, not applying the film themselves.
The AG's conclusion was therefore stacked on three statutory pillars: the express preemption clause in § 1392(d) for the state rule itself, the "render inoperative" prohibition in § 1397 for the businesses that would carry out a lower state standard, and the architecture of Standard No. 205 itself, which sets a numerical floor that any state below-floor rule cannot meet. A state rule allowing 35% transmittance violates all three.
Common questions
Could a NC law have allowed darker tint than the federal 70% on the front windshield and front side windows?
No. The 70% federal standard for windows "requisite for driving visibility" was the legal floor. A state rule allowing 35% on those windows would conflict directly with FMVSS 205 and be preempted under 15 U.S.C. 1392(d).
What about windows behind the driver, like rear side windows or the rear windshield?
The AG opinion focused on the federal floor as it applies to windows used for driving visibility. The federal standard had different categories for cars vs. multipurpose passenger vehicles, and for rearmost windows used vs. not used for driving visibility. States have generally followed the federal architecture, allowing darker tint on rear windows than on the windshield and front side windows. The preemption analysis applies window-by-window based on whether federal rule sets a transmittance requirement for that window.
Could NC apply a stricter tint rule than the federal standard?
Yes for state-purchased vehicles. The § 1392(d) exception lets a state impose a higher standard for vehicles the state itself buys for its own use. The exception did not authorize stricter regulation of the general public; that would also be preempted if it required the same window to meet a non-identical state standard, though courts have generally read "identical" with some flexibility for state rules that prevent something the federal standard does not address.
Why did the federal "render inoperative" provision matter?
Because it catches the businesses that install tint, not just the manufacturers of the glass. A tint shop that puts film on a window bringing combined transmittance below the federal floor is, on the federal reading, rendering the federally-required design inoperative. The penalty is up to $1,000 per violation. That federal exposure is what makes legitimate tint shops insist on staying above the federal floor on regulated windows, even when state enforcement is loose.
Did this AG opinion become a NC statute?
The opinion was a legal advisory to the DMV Commissioner about what NC could and could not enact. NC subsequently passed and amended its own window tint statute (G.S. 20-127), which has historically tracked the federal floor for windows requisite for driving visibility and allowed darker tint elsewhere, mirroring the federal categories. Anyone checking the current NC rule should look at the current G.S. 20-127 and the medical-waiver provisions in subsections of that statute.
Source
- Landing page: https://ncdoj.gov/opinions/motor-vehicles-regulations-of-dark-shaded-windows-preemption/
Original opinion text
Requested By: William S. Hiatt, Commissioner of Motor Vehicles
Question: Would a State statute or regulation allowing 35% light transmittance through windows in motor vehicles be preempted by current federal safety laws and standards regulating this same subject matter?
Conclusion: Yes.
The National Traffic and Motor Vehicle Safety Act of 1966 authorized the National Highway Traffic Safety Administration (NHTSA) to issue Federal Motor Vehicle Safety Standards for new motor vehicles and items of motor vehicle equipment. "Motor vehicle equipment" is defined in the Act, 15 USCS § 1391(4) as:
"(4) 'Motor vehicle equipment' means any system, part, or component of a motor vehicle as originally manufactured or any similar part or component manufactured or sold for replacement or improvement of such system, part, or component or as any accessory, or addition to the motor vehicle, and any device, article, or apparel not a system, part, or component of a motor vehicle (other than medicines, or eyeglasses prescribed by a physician or other duly licensed practitioner), which is manufactured, sold, delivered, offered, or intended for use exclusively to safeguard motor vehicles, drivers, passengers, and other highway users from risk of accident, injury, or death."
Safety Standard No. 205, "Glazing Material", sets performance requirements for glazing materials in new motor vehicles and those sold as replacement equipment. Standard No. 205 requires that glazing materials for use in motor vehicles conform to the American National Standard "Safety Code for Safety Glazing Materials for Glazing Motor Vehicles Operating on Land Highways" (ANSZ26). This standard requires specific amounts of light transmittance and abrasion resistance.
Standard No. 205 requires 70% light transmittance in all windows in passenger vehicles. Multipurpose passenger vehicles, motor homes, and trucks are required to have 70% light transmittance in the windshield and windows to the immediate right and left of the driver and the rearmost windows if used for driving visibility.
15 USCS § 1397(a)(2)(A) provides as follows: "(2)(A) No manufacturer, distributor, dealer, or motor vehicle repair business shall knowingly render inoperative, in whole or part, any device or element of design installed on or in a motor vehicle or item of motor vehicle equipment in compliance with an applicable Federal motor vehicle safety standard, unless such manufacturer, distributor, dealer, or repair business reasonably believes that such vehicle or item of equipment will not be used (other than for testing or similar purposes in the course of maintenance or repair) during the time such device or element of design is rendered inoperative. For purposes of this paragraph, the term 'motor vehicle repair business' means any person who holds himself out to the public as in the business of repairing motor vehicles or motor vehicle equipment for compensation."
Whoever violates this section is subject to a civil penalty of up to $1,000 for each such violation. The combination of tinting film and glazing must be at least 70% light transmittance in windows requisite for driving visibility.
15 USCS § 1392(d) provides as follows:
"Whenever a Federal motor vehicle safety standard established under this title is in effect, no State or political subdivision of a State shall have any authority either to establish, or to continue in effect, with respect to any motor vehicle or item of motor vehicle equipment any safety standard applicable to the same aspect of performance of such vehicle or item of equipment which is not identical to the Federal standard. Nothing in this section shall be construed to prevent the Federal Government or the government of any State or political subdivision thereof from establishing a safety requirement applicable to motor vehicles or motor vehicle equipment procured for its own use if such requirement imposes a higher standard of performance than that required to comply with the otherwise applicable Federal standard."
Congress may preempt State law by so stating in express terms. California Federal S. & L. Assn. v. Guerra, 93 L Ed 2d 613. Therefore, a State statute or regulation allowing 35% light transmittance through windows in motor vehicles would conflict with Standard No. 205 which requires 70% light transmittance in windows requisite for driving visibility and would be preempted by the federal law. 15 USCS § 1392(d).
LACY H. THORNBURG
Attorney General
Mabel Y. Bullock
Assistant Attorney General