Window tint: 50% front side windows, 35% rear, 3% tolerance

Wis. Stat. § 347.43 requires safety glass in every window of a Wisconsin motor vehicle built after January 1, 1936, but it fixes no light-transmission figure. The section instead carries a cross-reference to ss. Trans 305.32 and 305.34 of the Wisconsin Administrative Code, and that is where the percentages actually live. Trans 305.32 was created by Register, February, 1996, No. 482, effective March 1, 1996, and its tinting subsections have not been renumbered since.

For the vent and front side windows, Trans 305.32(4)(b) allows exactly three things. The glass may be tinted by the manufacturer of the glazing and installed as part of the original manufacturing process. Film may be applied to the inside of the glazing so long as glass plus film together pass at least 50 percent of the visible light striking the window, and that film may not be reflective. Or film passing at least 35 percent may be applied under the medical recommendation described below. Nothing else qualifies, so a 35 percent front film sold as legal in a neighboring state is a violation the moment it is applied to a Wisconsin car without the physician's statement.

The rear window and the rear side windows are both governed by a 35 percent floor, again non-reflective, under Trans 305.32(5)(b)2. and Trans 305.32(6)(b). Wisconsin does not follow the common pattern of allowing any darkness behind the driver: a limousine-dark rear side window is as unlawful here as a dark front one, unless the glass itself came that way from the glazing manufacturer. Trans 305.32(5)(b)3. adds a consequence most drivers miss. If the rear window does not transmit at least 60 percent of the visible light striking it, the vehicle must carry an outside rearview mirror on both the left and the right side of the driver's compartment. Any legal 35 percent rear film therefore triggers the two-mirror requirement, which is enforced alongside Trans 305.26 and Wis. Stat. § 347.40.

The windshield is handled separately by Trans 305.34(6). Film or other nontransparent material may be attached only to the part of the windshield that is both outside the windshield critical area and above the horizontal line marked "A" by the glass manufacturer, and if no such mark was affixed by the manufacturer, no window tinting film may be attached to the windshield at all. Trans 305.05 defines the windshield critical area as the portion normally used by the driver for necessary observations to the front, including the areas normally swept by a factory installed windshield wiper system.

Wisconsin's medical exception, in Trans 305.32(4)(b)3., is unusual in both who may issue it and what must be carried. The recommendation may come from a physician or from a Christian Science practitioner treating the owner or an immediate family member of the owner, and it lowers the front side and vent window floor from 50 percent to 35 percent. There is no state-issued placard or DMV permit. Instead the driver must carry a written statement in the vehicle at all times identifying the patient, the medical condition justifying the recommendation, whether the condition is temporary or permanent, and the vehicle by make, model, year and vehicle identification number. The film must be removed when the vehicle is sold, when the person for whom the recommendation was made no longer resides in the owner's household, or when a temporary condition expires.

Trans 305.03 makes it unlawful to operate, or allow to be operated, any vehicle on a Wisconsin highway that does not conform to chapter Trans 305, and Trans 305.04 sets the penalty by reference to Wis. Stat. § 110.075(7): a forfeiture of not less than $10 nor more than $200 unless another statute provides otherwise. A safety-glass violation charged under the statute itself carries the same $10 to $200 range under Wis. Stat. § 347.50(1).

Wisconsin runs no periodic safety inspection for passenger cars, so tint is a roadside matter. Wis. Stat. § 110.075(2) provides that when directed by any traffic officer or motor vehicle inspector the operator of any motor vehicle shall stop and submit the vehicle to inspection, and it lists glass among the items to be checked. Under § 110.075(5) the officer may issue a repair order that the owner or driver must then satisfy, and under § 110.075(4) a vehicle found unsafe for operation may be ordered off the highway until it has been repaired. If the vehicle is then found to conform, § 110.075(3) directs that an official inspection sticker be issued, and that sticker exempts the vehicle from inspection for one year. The only recurring test Wisconsin requires is the emissions inspection under Wis. Stat. § 110.20, which the department operates only in the counties identified under § 110.20(4), and it is an emissions and equipment check tied to air quality rather than a tint check.

The reasonable-cause limit on equipment stops in Wis. Stat. § 349.02(2)(a) reaches chapters 341 to 346 and does not extend to the Trans 305 equipment rules, and that paragraph expressly does not apply to a traffic officer or motor vehicle inspector performing duties under § 110.075(2).