Is It Illegal to Tint Your Windshield?

The Federal Floor: FMVSS 205 and the 70% Rule

The National Highway Traffic Safety Administration (NHTSA) — the U.S. Department of Transportation agency created under the National Traffic and Motor Vehicle Safety Act of 1966 — sets the baseline rule for automotive glass through Federal Motor Vehicle Safety Standard No. 205, “Glazing Materials.” FMVSS 205 incorporates by reference the American National Standards Institute and Society of Automotive Engineers standard ANSI/SAE Z26.1-1996, which classifies windshield glass as “AS-1” and requires it to maintain a luminous transmittance — the percentage of visible light that passes straight through — of no less than 70%.^[1]

That 70% floor applies to the entire windshield, not just a portion of it — and it’s a combined measurement of the factory glass plus anything bonded on top of it. Original equipment windshields typically ship between 70% and 80% VLT because of the plastic interlayer and mild factory tinting baked into the glass at the plant. Layer even a nearly clear aftermarket film over that factory glass, and the combined transmittance frequently drops below the federal minimum — turning compliant glass into non-compliant glass with a single install.^[9]

The Shade Band Exception and the AS-1 Line

Federal regulators built in one exception for sun glare. Glass manufacturers permanently etch the edge of a windshield with the designation “AS-1” and a small downward-pointing arrow — the AS-1 line. Everything below that arrow is the primary viewing area and must meet the 70% minimum. Everything above it, the shade band, carries no federally specified minimum transmittance at all, which is why an opaque tinted strip across the very top of the glass is legal while the same darkness lower down is not.^[6] If a particular windshield has no visible AS-1 marking, federal guidance limits the shade band to the area above the top of the rearview mirror mount — in practice, roughly the top five to six inches of the glass.

That distinction is the reason a private citizen who buys a roll of film and applies it themselves in their own driveway is not, in that moment, breaking federal manufacturing law — the federal government does not regulate how individuals use their own vehicles on public roads, only what commercial businesses may do to them.^[2] That gap is exactly what state operational law exists to close, and it’s where most drivers actually get cited.

Why a “Legal” State Tint Percentage Still Doesn’t Protect the Shop

Because states control day-to-day vehicle operation, a state legislature is free to write a law allowing darker glass than the federal standard contemplates, and that law is fully valid for its intended purpose: keeping a state trooper from writing a driver a ticket. What it cannot do is excuse a commercial tint shop from federal law. Under the doctrine of federal preemption, a state statute that appears to legalize a below-70% windshield only shields the driver from a state citation — it has no effect on the separate federal obligation the installer owes under 49 U.S.C. § 30122(b).^[3]

NHTSA has repeated this point in multiple interpretation letters: no state has the authority to grant a commercial business an exemption from a federal motor vehicle safety standard. A shop that installs windshield tint below the federal floor remains exposed to federal civil penalties even in a state whose own vehicle code would allow that same darkness.^[3]

What State Vehicle Codes Say About the Windshield

State enforcement is where nearly every driver actually encounters this rule — during a routine stop or an annual safety inspection, not a federal audit. The table below shows how eleven state vehicle codes describe the legal windshield tint area, each tied to the primary statute or administrative code section that sets it. This is an illustrative sample, not a full fifty-state compilation, and the specific measurement varies by state — a flat inch count from the top of the glass, a distance measured from the driver’s seat, or the AS-1 line described earlier, whichever a given state’s code applies.

Commercial Trucks Face a Stricter, Federally Preempted Rule

Passenger-car drivers answer to their state’s vehicle code, but commercial motor vehicles operate under an entirely separate federal regime enforced by the Federal Motor Carrier Safety Administration (FMCSA), which preempts conflicting state tint rules for those vehicles. FMCSA regulations hold commercial motor vehicles to the same 70% light-transmission floor for the windshield and the windows immediately to the driver’s left and right.^[7]

The trucking industry has pushed back on this directly. The International Window Film Association petitioned FMCSA for an exemption allowing darker commercial truck glass, arguing that reduced glare and heat load would improve driver comfort and cut cabin cooling costs on long hauls. FMCSA denied the request, finding the industry hadn’t shown that operating with darker glazing would achieve a level of safety equivalent to complying with the existing 70% standard.^[8]

The Medical Exemption — and Its Federal Contradiction

Most states run a formal administrative process letting a driver with a documented light-sensitivity condition legally exceed the standard tint limit. Conditions that commonly qualify include lupus, melanoma and other skin cancers, albinism, solar urticaria, xeroderma pigmentosum, and erythropoietic protoporphyria — each involving a real physical risk from ordinary sunlight exposure, not simple discomfort.

The process typically requires a licensed physician or optometrist to certify the medical need, with that certification submitted to the state’s Department of Motor Vehicles or Department of Transportation for review. Pennsylvania, for example, routes applications through Form MV-402 to the PennDOT Medical Advisory Board.^[10] An approved driver must carry the physical exemption certificate in the vehicle and produce it on request during a stop. Colorado is a notable exception that currently recognizes no medical tint exemption at all. Iowa no longer issues new medical exemptions, but preserves certain exemptions granted before July 4, 2012 for the documented vehicle while it remains in qualifying use — drivers in both states should confirm current status directly with their state DOT rather than assume a categorical rule.

Why the Windshield Camera Makes This a Mechanical Problem, Not Just a Legal One

Modern passenger vehicles increasingly rely on a forward-facing optical camera mounted directly behind the windshield, usually built into or next to the rearview mirror housing, to power Automatic Emergency Braking, Forward Collision Warning, Lane Keep Assist, and Adaptive Cruise Control. That camera is calibrated at the factory to the exact thickness, curvature, and light-transmission properties of the original glass it looks through.

Adding aftermarket film changes both of the variables that camera depends on. A film that drops light transmission from 70% down toward 35% starves the camera’s low-light performance, degrading its ability to pick out a pedestrian in dark clothing or a lane line in rain or fog. The adhesive layer and polyester film also introduce a small amount of optical refraction — and at highway following distances, even a roughly one-degree bend in the light path translates to several feet of positional error in where the system believes an object actually is.

What Automakers Say in Writing

Subaru’s EyeSight documentation explicitly bans aftermarket windshield treatments and tinting within the dual-camera system’s field of view, warning that film-induced distortion prevents the cameras from correctly measuring distance and can disable the system.^[4] Honda’s technical service documentation instructs installers to “never apply a film or attach any objects to the windshield… that could obstruct the camera’s field of vision and cause the system to operate abnormally,” and notes that even minor nicks in the camera’s zone can disable the safety suite.^[5] Toyota Safety Sense guidance similarly warns against any aftermarket accessory that interferes with the forward recognition camera, since a disrupted view can disable the Pre-Collision System, pedestrian detection, and dynamic radar cruise control.

Civil Liability Beyond the Ticket

An illegal windshield tint citation is rarely the most expensive consequence. If a driver with a heavily tinted windshield strikes a pedestrian or another vehicle at night, plaintiff’s counsel in the resulting civil case can point to the tint as direct evidence that the driver couldn’t see the hazard in time to stop — and because the driver knowingly operated the vehicle in violation of a visibility statute, that argument can support a claim of gross negligence rather than ordinary negligence.

Liability isn’t limited to the driver. In South Carolina, the family of a pedestrian killed by a Nissan Rogue sued both the driver and the retail store that sold and installed the vehicle’s dark windshield tint, alleging the business’s violation of state and federal tint law contributed directly to the driver’s inability to see the pedestrian crossing at night.^[11] A liability waiver signed at the counter doesn’t reliably protect a tint shop in that scenario either — a private contract generally can’t waive a business’s exposure for committing what amounts to an illegal act that contributes to a fatality.