FAMILY HANDYMAN, GETTY IMAGESSchool buses are pretty easy to recognize. And for good reason. Their bright yellow paint job, flashing red lights, fold-out stop signs, and large rectangular shape are iconic and easy to spot, which is intentional to make sure drivers are paying extra attention when they're on the road.But there may be another unique feature that often gets overlooked. School buses often feature long black stripes that run horizontally along the side. They aren't decorative trim or rubber bumpers, but form part of the bus body's reinforcement.Learn what those school bus stripes, called rub rails, actually do, why they're manufactured that way, and why the design can vary.What the Black Stripes on a School Bus Actually DoRub rails are used to reinforce the sides of a school bus and protect its exterior panels from damage. Many state standards call for 16-gauge steel or another material with similar strength, although exact requirements can vary. They generally use a ribbed or corrugated shape rather than a flat strip of metal.AdvertisementAdvertisementThe placement of rub rails isn't random. School bus construction standards position them near important parts of the passenger compartment and body structure. They attach to the body posts and other upright structural members, which adds reinforcement along the sides while helping shield the exterior panels from everyday contact and damage.They're also commonly painted black because school bus paint and finish specifications in many states call for black rub rails.Are All School Buses Designed the Same?No. Requirements can differ by state, and individual school districts may also have their own purchasing specifications.The National Highway Traffic Safety Administration recognizes rub rails as part of a school bus's exterior, but the rails themselves aren't treated as body-panel joints under the federal joint-strength standard. The federal rule describes them as "support members such as rub rails which are entirely outside of body panels."AdvertisementAdvertisementThat distinction matters because the federal rule focuses specifically on the strength of the joints connecting the bus's body panels. States can set their own more specific rules for how rub rails are built and where they're placed.The number of stripes will depend on the bus type, manufacturer design, and applicable state requirements. Some states require one rail at seat-cushion level, another at or just above the floor line, and a rub rail or similar horizontal reinforcement near the bottom of the side skirt. Others also include a rail near the bottom edge of the windows.That's why some buses have more black stripes than others. Their exact placement may vary, but the rails serve the same general purpose of reinforcing and protecting the bus body.So the next time a school bus passes by, those black stripes may stand out a little more.SourcesU.S. Code of Federal Regulations, "School bus body joint strength"Texas Department of Public Safety, "School Bus Specifications"RELATED:The Real Reason Aluminum Foil Has a Shiny Side and a Dull SideThink Adirondack Chairs Are Uncomfortable? You're Using Them WrongWhy You Shouldn't Crush Aluminum Cans Before Recycling