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Article: The History of Seat Belt Development

Compartmentalization | State Laws and Requirements | Seatbelt FAQ | Web Resources


What does compartmentalization mean? The term is at the heart of the Great Seat Belt Debate. It was coined during the 1967 and 1972 Series 1 and Series 2 “School Bus Passenger Protection” collision tests conducted at the University of California at Los Angeles. Although not an element of compartmentalization, the UCLA researchers concluded that after high back seats, next in importance to school bus passenger collision safety is the “use of a three-point belt, a lap belt or other form of effective restraint.”

Other UCLA conclusions included:

  • High back seats of 28 inches or more greatly contribute to the compartmentalization of passengers thereby reducing the chances of injuries sustained by passengers being hurled against one another, regardless of their size. Seatback height for school buses should not be less than 28 inches.”
  • Lap belts should not be used with low seat back seats as this would lead to head and chest injuries caused by belted passengers rotating forward and striking the upright backrest ahead.
  • School bus seats should not be provided with rigid protruding structures such as handgrips, handrails or similar injury-producing fixtures.
  • Lap belts would provide substantial additional protection if used in combination with high-back seats equipped with additional efficient padding on the rear panel of the backrest ahead.
  • Standees should not be permitted.
  • Seat belts are not recommended for school buses equipped with seats with hard surfaces, a metal bar along the backside of the top of the frame ahead, weak seat frames, or low-back, 24-inch seats.

Compartmentalization became the heart of the federal government’s policy of school bus safety. The concept of compartmentalization envisions children riding in a cocoon or compartment surrounded by an energy-absorbing, passive occupant protection system. Some industry experts use the metaphor “egg carton” as in cushioning the eggs inside, to describe compartmentalization.

This is why standees on school buses should never be permitted.

However, the National Transportation Safety Board (NTSB) found that compartmentalization is “incomplete” and “does not protect passengers during lateral impacts with vehicles of a large mass, in rollovers and from ejection.” According to NTSB, an occupant crash protection system should be developed that would protect passengers in most accident scenarios.

In response, NHTSA updated FMVSS 207, 208, 210, and 222 to enhance compartmentalization with mandatory requirements for equipping all small Type A school buses manufactured as of September 2011 with 3-point lap/shoulder seat belts. Partly due to compartmentalization and the higher cost of larger school buses equipped with these 3-point seat belts, NHTSA only published voluntary standards for equipping school buses that weigh more than 10,000 pounds with the occupant securement systems.

In addition to padding, today’s seats also must have a steel inner structure that bends forward to help absorb energy when a child is thrown against it, especially those students seated behind who may not be wearing their seat belt. Also, of course, the seat is required to be anchored to the floor strongly enough that it will not pull loose during this bending action, or during collisions. Federal regulation requires each passenger seat to be anchored to the school bus floor and withstand 15,000 lbs. pulling force per seat. The floor itself must be strong enough that it will not be bent or torn by the pulling action of the seat anchors. The NHTSA final rule in 2008 also required quasi-static testing of these seats to ensure that belted as well as unbelted passengers remain protected, or compartmentalized, in the event of a crash.

Seat manufacturers CE White, IMMI/Safeguard and Takata/M2K have also solved the potential of losing passenger capacity on school buses with seat belts by creating seats flexible enough to fit two larger students, such as high schoolers, or three smaller elementary or some middle schoolers per seat.

Seatbacks in school buses are also now made higher, wider and thicker than before. After the most recent final rule, seatbacks will be required to be at least 24-inches high. All metal surfaces are covered with energy-absorbing padding. This structure must pass rigid test requirements for absorbing energy, such as would be required if a child’s body were thrown against the padded back. The equivalent of a seat back, called a barrier, is placed in front of the first seat at the front of the bus.

Finally, seatbacks cannot be farther apart than a distance that is deemed safe. Clearly, if the seats are too far apart, the child could be thrown too far before being cushioned and/or could be thrown outside the compartment altogether. Following further research by the federal government, 24 inches spacing was established as the optimal distance between school bus seats.

“In compartmentalization, the crash forces are absorbed by the vehicle structure which is designed to protect the occupant,” said Charles Hott. NHTSA’s school bus specifications engineer. “In an occupant restraint system in general passenger vehicles, the crash forces are absorbed by the body of the occupant.”

Source: School Bus Passenger Protection; Institute of Transportation and Traffic Engineering, University of California at Los Angeles, by Severy, Derwyn M.; Brink, Harrison M. and Baird, Jack D. (Los Angeles, CA 1967).

State Laws and Requirements

Of the nine states to pass school-bus, seat-belt laws, only Louisiana has been unable to fully implement the requirement to install belts in new buses due to insufficient funding.

The law in the Pelican State requires supplemental funding to be made available by the state legislatures in order to enforce two-point, lap seat belts. Texas was in the same predicament until June 2017, when the state legislature passed and Gov. Greg Abbott approved a new three-point, lap-shoulder belt to replace the old one that requires all school district purchases of new school buses to included the three-point occupant restraints, unless the local school board votes in a public meeting to defer the requirement due to lack of funds. The previous law passed in 2007 made implementation reliant upon funds being appropriated by the legislature.

Louisiana passed its law in 1999, the same year as Florida, which began requiring two-point belts on buses in 2001 but doesn’t make funding available to school districts. Charlie Hood, the retired director of school transportation at the state Department of Education and currently the executive director of the National Association of State Directors of Pupil Transportation Services (NASDPTS), said funding has never been an issue, as the cost of the restraint systems is less than 2 percent of the overall purchase cost of a new school bus.

“Districts have absorbed that upcharge over the years,” he added.

Hood said that, as of July 3, 2013, about 12,000 of the state’s 15,000 school buses in daily service are equipped with lap seat belts.

New Jersey updated its existing law in August 2018 to require lap-shoulder belts from the previous requirement of lap belts.

Meanwhile, California, Florida, New Jersey and Texas require students to use the restraints. California student riders must also be taught how to use the three-point restraints “in an age-appropriate manner.” New York allows individual school boards to decide if they will provide lap or lap-shoulder belts on buses but does not mandate students to use them.

Nevada passed its three-point law in June 2017, and Diana Hollander, state director of transportation at the Nevada Department of Education, said requirements that students use the restraints will be written into regulation before the mandate went into effect for the 2019-2020 school year.

California and Florida law stipulate that transportation providers first allocate lap-shoulder belts on elementary-school routes. Both state laws and the one in New Jersey also protect any rider, school district or organization operating a school bus from being ticketed for not wearing seat belts.

Texas school districts must require students to wear their three-point seat belts on buses equipped with them, and they may develop a disciplinary policy to enforce seat belt usage. Texas law also requires student training on the lap-shoulder systems.

Nevada requires all new school buses in operation by July 1, 2019, to be equipped with lap-shoulder seat belts. Arkansas also has a law on lap-shoulder seat belts but first requires local voters to approve property tax increases to pay for them. However, if seatbelts are installed on school buses, state law requires that students wear them. Maine has a similar usage law.

Individually, local school districts in other states may voluntarily install seat belts. The National Congress on School Transportation in 2005 passed a resolution that urged the National Highway Transportation Safety Administration to change the federal regulations to only allow lap-shoulder seat belts in school buses 10,000 pounds GVWR and less. NHTSA’s revised FMVSS 222 published in 2010 requires these three-point restraint systems in small school buses while leaving to school districts and states the decision on requiring three-point belts on school buses over the 10,000-pound GVWR threshold.

Iowa became the latest state to require three-point lap/shoulder seatbelts on all new school buses ordered on or after Oct. 2, 2019. The Iowa Administrative Code states that adding a lap/shoulder belt would cost an additional $123 per seating position.

STN Seatbelt FAQ

Common Seatbelt Questions Discussed by Industry Expert

School Transportation News shared questions and concerns from readers about implementing lap/shoulder seatbelts in school buses with former National Child Passenger Safety Board member Charles Vits. Vits is also the former market development manager for IMMI seat and seatbelt brand SafeGuard. He retired at the end of 2020. Vits provided answers and guidance.

  1. What information is provided on injuries from the seatbelts? There is always a potential for a seatbelt injury in a serious crash, but the more severe the crash, the greater the likelihood of a serious injury or fatality when not wearing any belt. There have been studies done by both the NTSB and NHTSA that conclude in a crash it is more dangerous to be unbelted than it is to wear a lap-shoulder belt or even a lap belt. So as far as concerns for belt induced injuries, it’s better to have a seatbelt injury than a fatal injury.
    There was a crash near the Tennessee-Georgia border back in 2000, where a train impacted a bus that was crossing the railroad tracks. The impact was so severe that the bus body separated from the chassis. The school bus driver was wearing a lap/shoulder belt that broke during the crash but received minor injuries. Of the four passengers that were not ejected from the bus, two were fatally injured, one sustained serious injury and the one restrained by a lap belt received minor injuries. Read the report from the NTSB.  
  2. When children are buckled up, school bus drivers can’t see the children. Can we lower the seatbacks? Seatback height was regulated to the current high-back seat height in 2009, based on the increasing height of our students and the greater potential for the taller student to ride over the previous lower height seat back in a frontal crash. Reverting to the lower height seatback would mean two things.
    First, there would have to be 100-percent usage of lap/shoulder seatbelts by every single passenger. On the off chance, a child doesn’t wear his/her seatbelt for the trip, that child would be dependent on compartmentalization with the higher seat back for their best protection.
    Second, if the height of the seats is lowered, then the seatbelt shoulder anchorage will too have to be lowered by that same four inches. Therefore, the taller students wouldn’t be able to use the seatbelts as effectively. So, while the visibility of the children is a valid concern, lowering the seatbacks, would create greater issues for student protection.
  3. Who is liable when students don’t buckle up? Liability differs based on states and districts. However, districts are just as liable now for safe transportation on unbelted school buses, and when students are not seated properly for their compartmentalization protection. When a crash occurs, we will all be in court. Those who have been proactive about student protection will be in a far better position to argue liability than those who have limited their student protection actions to only meeting minimum requirements.
    When implementing lap/shoulder belts, districts and states must have verbiage discussing the usage policy. For instance, the Montana state seatbelt law mandates the use of belts if the vehicle is equipped with belts. This includes school buses if they are equipped. California code explicitly states that belts must be worn in equipped school buses. However, real enforcement comes from the district when there is an enforceable usage policy. If districts choose to install the belts, then it is up to the district to set a policy on how student belt usage works. Districts are adding the policies into their student code of conduct on the bus and disciplining the child accordingly if they choose not to wear them. These disciplinary actions include warnings, suspension from the bus, etc.
    A Montana district that recently added the safety restraints said it would be the same procedures as an airplane. The school bus driver walks the bus aisle once and makes sure everyone is wearing their belts.
  4. If I install seatbelts, will I lose seating capacity? In 2007, flexible seating technology was introduced to the industry. Prior to that, you would lose seating capacity if you installed lap/shoulder belt-equipped seats. However, with the flexible seating technology, meaning three smaller elementary students or two larger high students per seat, you are not losing capacity. An 84-passenger bus remains an 84-passenger bus, etc.
    For those districts sitting three middle and/or three high school students to an unbelted seat, they might interpret a capacity loss. However, depending on the size of those kids, the aisle-seated student won’t be receiving proper compartmentalization protection. Vits explained that compartmentalization does not fully work with kids sitting in the aisle, positioned outside of their compartments. According to experts, that should not be happening in the first place. Information from NHTSA explains “The Number of People Who Can Safely Sit on a School Bus Seat.” 
  5. How much time does it take to adjust the flexible seating seatbelt onto a student? It takes seconds to adjust the flexible seat buckle from a first grader to a 12th-grader, Vits said. It’s something the children can do on their own. Either they slide the buckles into place, or the buckles will automatically slide into adjustment, based on the size of the child. The shoulder height adjuster is then lowered to provide them with the most comfort at their neck.
  6. What if there is a fire on the bus and students can’t get out? Just like anywhere else in our schools, evacuation drills need to be conducted to prepare a response in the event of an emergency. When school buses are equipped with lap-shoulder belts, an unbuckling practice should also be included with the evacuation drill so unbuckling becomes an automatic response when the diver says “unbuckle” or “evacuate”.
    The Iowa Pupil Transportation Association (IPTA) did a study on evacuation times in July 2019 for children with a seatbelt and children without. It took a little over a minute for children to evacuate from the bus with no seatbelts and about 45 seconds to evacuate with seatbelts. Although the results may seem illogical, we can conclude that the introduction of belts makes no difference in evacuation time. This has been proven in real-world, belt-equipped school bus fires that have already occurred. Successful, quick evacuations were reported. Read more about the IPTA evacuation exercise at
    Vits said the other benefits to lap/shoulder belts in an emergency is that they reportedly help with behavior. Using the belts creates a calmer and quieter bus. That allows children to immediately and more clearly hear the bus driver directions to evacuate. STN has covered articles on lap/shoulder belts and the influence on behavior that the restraints have.

Web Resources

Presented below are links to web pages devoted to seatbelts in motor vehicle transportation and in school buses.

Final Rules:

  • School Bus Passenger Seating and Crash Protection: Seating Systems, Occupant Crash Protection, Seat Belt Assembly Anchorages 
    Final rule effective Oct. 21, 2011, that upgrades the school bus passenger crash requirements of FMVSS 222

    • Requires new school buses of 4,536 kilograms (10,000 pounds) or less gross vehicle weight rating (GVWR) (“small school buses”) to have lap/shoulder belts in lieu of the lap belts currently required.
    • Sets performance standards for seat belts voluntarily installed on school buses with a GVWR greater than 4,536 kilograms (10,000 pounds) (“large school buses”).
    • Raises the height of seatbacks from 508 mm (20 inches) to 6102 mm (24 inches) on all new school buses and requiring a self-latching mechanism on seat-bottom cushions that are designed to flip up or be removable without tools.
    • Each state or local jurisdiction may decide whether to install seat belts on these large school buses.


Web Sites:

  • Alabama School Bus Seat Belt Pilot Program: A three-year study to assess the impact of lap/shoulder restraint systems on passenger safety. The program is a result of a study group formed by Alabama Gov. Bob Riley in November 2007 following a fatal school bus crash in Huntsville. The final report was released in the fall of 2010. Study authors admitted that pilot tests at school districts failed to incorporate data from new flexible-seat technology that allows for either two or three students to be bucked up per seat, depending on the student’s age and size (two per seat for large middle school students or high school students; three per seat for elementary school and most middle school students).
  • National Highway Traffic Safety Administration: School Bus Safety
  • A public awareness website by IMMI describing the benefits of occupant securement systems on school buses.

  • School Bus Safety: The Seat Belt Issue
    A review of the issue by the New Brunswick Department of Education, January 2002 [PDF file]

  • IMMI of Westfield, Ind., offers the SafeGuard 3-point lap/shoulder belt securement system. The company’s Web site describes IMMI’s four-year research project, including half a dozen full-scale dynamic bus crash tests and more than 70 sled tests, to develop a lap and shoulder belt occupant protection system for school buses.

  • HSM’s C.E. White line features the Student Safety Seat System, a 3-point lap/shoulder belt system.

  • Syntec Seating Solutions is another school bus seat manufacturer that offers a 3-point lap/shoulder belt solution for school districts that need to fit either two or three students per seat depending on their age and size.

  • Users interested in learning the arguments in favor of seat belts on large school buses should visit National Coalition for Seat Belts on School Buses. This site offers extensive documentation about the pro seatbelt position.

  • The Network of Employers for Traffic Safety offers guidance about increasing seat belt usage among employees.

Position Papers:

    • School Bus Occupant Protection
      A Consideration of the Issues for State Policy-Makers
      By the National School Transportation Association, March 15, 2012

Advisory Letters:

  • Texas SB 693
    Read a letter from Sen. Sylvia Garcia to all state school district superintendents, school boards, transportation departments and state agencies assisting in the implementation of the law that goes into effect for model-year 2018 school buses that requires them to be equipped with three-point, lap-shoulder seat belts.