Modeling Real People in Real Buses: Implications Concerning Tire, Axle and Vehicle Weights

The current certification requirements under CFR 49, Part 567 state that GVWR of a motor vehicle shall not be less than the sum of the unloaded vehicle weight, rated cargo weight and 150 pounds times the number of designated seating positions. Actual occupant weight distributions versus certified weight per occupant seat causes a potential conflict between a vehicle's in-use weights versus its certified GVWR. Population weight distributions were developed based upon The Center for Disease Control's (CDC) publication of 2007 - 2010 anthropometric reference data and publically available weights of a special population from high school football teams. For five buses from small (18-seat) to large (55-seat), key parameters were measured. The weight distributions and bus parametric data were combined in a probabilistic analysis to explore the probability that passengers and rated cargo would result in weight distributions that exceeded tire load capability, Gross Axle Weight Rating (GAWR), or Gross vehicle Weight Rating (GVWR). The scope of the paper does not investigate whether increasing the required weight per seat would produce net benefit, but, given historical usage and understandings and recent requirements for objective test criteria, an objectively derived and, if judged necessary, updated occupant weight per seat requirement is suggested. Results demonstrated that load conditions and usage restrictions are identifiable that decrease the probability of operating in a condition that exceeds a tire or vehicle weight rating. The analysis of this paper supports that a median unclothed adult weight of at least 79.3 kg (175 pounds) which would represent an equal male and female population of all race and ethnicity in the United States of America should be considered.