NHTSA Aiming to Improve Rollover Structural Integrity of Large Buses

Aug. 6, 2014

The National Highway Traffic Safety Administration (NHTSA) is issuing a notice of proposed rulemaking (NPRM) on a new Federal motor vehicle safety standard to enhance the rollover structural integrity of certain types of large buses—generally over-the-road buses (of any weight) and non-over-the-road buses with a gross vehicle weight rating (GVWR) greater than 26,000 pounds.

The agency is proposing performance requirements that new large buses of these types must meet in a test in which the vehicle is tipped over from an 800- millimeter raised platform onto a level ground surface. The performance requirements would ensure that these vehicles provide a sufficient level of survival space to restrained occupants in rollover crashes.

The performance requirements would also ensure that seats and overhead luggage racks remain secured and window glazing attached to its mounting during and after a rollover crash, and would ensure that emergency exits remain closed during the rollover crash and operable after the crash.

This NPRM is among the rulemakings issued pursuant to NHTSA's 2007 Approach to Motorcoach Safety and DOT's Departmental Motorcoach Safety Action Plan. In addition, establishing roof strength and crush resistance requirements, to the extent warranted under the National Traffic and Motor Vehicle Safety Act, would fulfill a statutory provision of the Motorcoach Enhanced Safety Act of 2012 (incorporated and passed as part of the Moving Ahead for Progress in the 21st Century Act).

The plan was developed to respond to several National Transportation Safety Board
(NTSB) recommendations, and also to address several crashes that occurred after those recommendations were issued. In 2009, DOT issued a Departmental Motorcoach Safety Action Plan, which outlined a Department-wide strategy to enhance motorcoach safety, addressing additional factors such as driver fatigue and operator maintenance issues.

NHTSA's Approach to Motorcoach Safety identified four specific areas where NHTSA could most effectively address open NTSB recommendations and potentially improve motorcoach safety. The four priority areas were: Reducing the risk of passenger ejection from the motorcoach, improving rollover structural integrity, enhancing emergency evacuation, and upgrading fire safety.
 This NPRM builds on the seat belt final rule by proposing to require those buses to meet increased structural integrity and other requirements to protect both restrained and unrestrained occupants in rollover crashes. An over-the-road bus is a bus characterized by an elevated passenger deck located over a baggage compartment. Some buses are excluded from this latter category, such as transit and school buses.

The following are the main proposed performance requirements that buses covered by this proposed rule must meet when subjected to the rollover structural integrity test:
    (1) Intrusion into the “survival space,'' demarcated in the vehicle interior, by any part of the vehicle outside the survival space is prohibited;
    (2) each anchorage of the seats and overhead luggage racks must not completely separate from its mounting structure;
    (3) emergency exits must remain shut during the test and must be operable in the manner required under FMVSS No. 217 after the test; and

    (4) each side window glazing opposite the impacted side of the vehicle must remain attached to its mounting such that there is no opening that will allow the passage of a 102 mm diameter sphere.