WASHINGTON – The U.S. government may adapt the formula it uses to write municipal-bus safety rules because the average passenger is getting heavier, a change that could lead to changes in bus design.

The Federal Transit Administration proposed raising the assumed average weight per passenger to 175 pounds from 150 pounds and calculating an additional quarter of a square foot per passenger for its testing procedures. The proposal was published in today’s Federal Register.

Bus manufacturers may choose to upgrade chassis, tires, wheels, brakes or suspensions to carry more weight, the transit agency said.