The Regulatory Framework
School bus glazing sits at the intersection of two federal motor vehicle safety standards, both administered by NHTSA[1].
FMVSS No. 205 (Glazing Materials)[2] is the foundational standard. It applies to all motor vehicles sold in the United States, including school buses, and defines the safety glazing classifications that any material must meet to be used in a vehicle. FMVSS 205 incorporates ANSI Z26.1 by reference, meaning the test methods and performance requirements in ANSI Z26.1 are the actual technical substance of the federal rule.
FMVSS No. 217 (Bus Emergency Exits and Window Retention and Release)[3] adds requirements specific to buses. It governs how glazing must perform during a crash (retention in the frame) and what is required of windows designated as emergency exits: force limits, operating instructions, and labeling.
Both standards must be satisfied. A glazing material that passes FMVSS 205 classification tests but fails window retention under FMVSS 217 is not compliant for use in a school bus.
ANSI Z26.1 and the AS Classification System
ANSI Z26.1 (American National Standard for Safety Glazing Materials for Glazing Motor Vehicles and Motor Vehicle Equipment Operating on Land Highways) defines 12 glazing types, numbered AS1 through AS12. Each type is defined by a combination of performance requirements for optical clarity, light transmission, impact resistance, and abrasion resistance. The “AS” designation appears as a marking on compliant glazing, along with the manufacturer name and certification number.
The classifications most relevant to school bus applications:
AS1 is the highest classification. It covers windshields. Requirements include light transmission of 70% or greater, extremely low optical distortion, and the highest impact resistance thresholds. AS1 glazing must pass a penetration resistance test and a head-form impact test. Only materials meeting the complete AS1 requirement set are permitted in the school bus windshield position.
AS2 covers side windows and rear windows in positions where clear outward visibility is required. Light transmission must be 70% or greater. The impact and abrasion requirements are less stringent than AS1 but remain specific. Side windows in the forward seating area of a school bus typically fall into this category.
AS3 covers glazing positions where light transmission below 70% is acceptable. Rear corner windows and some supplemental glazing positions may qualify.
AS10, AS11, and AS12 are the safety plastic classifications. AS10 applies to plastic glazing in non-windshield positions with no minimum light transmission requirement. AS11 covers plastic glazing for side window positions requiring 70% or greater light transmission. AS12 is the highest plastic classification, covering windshield applications.
Where Polycarbonate Qualifies
Polycarbonate can be certified under AS11 for side window positions requiring 70% or greater light transmission, and AS10 for positions without that requirement. At typical transit glazing thicknesses (4mm to 10mm depending on position and impact load), uncoated polycarbonate meets the light transmission floor but requires a hard coating to satisfy the abrasion resistance component of the applicable AS test.
ANSI Z26.1 Test 17 evaluates abrasion resistance using a Taber abraser: haze increase after 100 cycles under a 500-gram load. Uncoated polycarbonate exceeds the haze limit in this test. Properly coated polycarbonate passes. Coating selection is therefore not optional for school bus glazing: it is part of what makes the material certifiable to the applicable AS class.
Light transmission is evaluated across the 380-780nm wavelength range. Polycarbonate transmits at 88-90% in this range at typical glazing thicknesses. The challenge is maintaining that number after field use. Cleaning chemicals, abrasive contact, and UV exposure all reduce transmission over time. Coating durability determines whether the window stays within specification over a service cycle that, for a school bus, can span 10 or more years.
FMVSS 217: Retention and Emergency Egress
Beyond material classification, FMVSS 217 sets requirements for what happens to glazing during and after a crash. Two requirements are relevant to polycarbonate specification.
Window retention: During the crash pulse tests specified in FMVSS 217, glazing designated as an emergency exit must remain in its frame. The standard specifies the retention force the window must withstand when pushed inward, and separately the force at which a designated emergency exit window must release when pushed outward from the inside. Polycarbonate, because it does not shatter, is inherently advantageous in the retention test: the material deforms without fragmenting, and a properly designed frame system can maintain panel position through the required test sequence.
Emergency exit operation: Windows designated as emergency exits must be operable from the inside without special tools and within a specified force range. This is a design and hardware requirement as much as a material requirement, but it affects glazing specification because panel weight and frame design must permit operation within the force limits. Polycarbonate is significantly lighter than glass of equivalent thickness, which reduces the force required to operate push-out emergency exits.
FMVSS 217 also specifies minimum opening areas for emergency exits, labeling requirements, and exit marking locations. None of these directly limit the choice between glass and polycarbonate, but they constrain the panel geometry the glazing material must accommodate.
Specification Checklist for School Bus Glazing
For engineers writing polycarbonate glazing specifications for school bus applications:
Confirm the glazing position first: windshield, forward side window, rear side window, emergency exit window, or supplemental position. Each maps to a different AS classification and a different set of tests.
For side window positions, specify AS11 certification from the polycarbonate supplier. Request the certification number and verify the material is marked at the edge or corner per ANSI Z26.1 marking requirements.
Specify the hard coating by abrasion performance, not by brand. The coating must pass ANSI Z26.1 Test 17. Request test data showing haze increase after 100 Taber cycles at 500g load on the specific coating grade before committing to a supplier.
Account for chemical exposure. School bus windows are cleaned frequently with a range of agents. ANSI Z26.1 Test 20 evaluates chemical resistance using specified reagents including cleaning compounds. Request chemical resistance data for the cleaning agents actually used by the fleet operator.
For emergency exit windows, confirm that glazing panel weight and frame design together meet the force range specified in FMVSS 217 for exit operation.
Five Star’s School Bus Glazing Capabilities
Five Star Fabricating produces coated polycarbonate windows for mass transit applications including school bus platforms. Fusionite-coated polycarbonate satisfies the abrasion requirements for AS11 certification, and Five Star’s in-house lab tests to ANSI Z26.1 and ASTM D1003 for light transmission and haze on a per-production-run basis.
Five Star’s lab testing capabilities[4] include optical testing per ASTM D1003, Taber abrasion per ASTM D1044, impact testing per FMVSS 205 S5.3, and chemical resistance per ASTM D1308. Test data is available for specification review before production commitment.
Contact
To discuss school bus glazing specifications or request test data for a specific Fusionite coating grade, contact Five Star Fabricating in Twin Lakes, WI: +1 (262) 877-2171.
View mass transit glazing capabilities and submit a quote request at fivestarfabricating.com/applications/mass-transit.