The US Federal Transit Authority, similar to its Canadian counterpart, the Canadian Transit Authority, is responsible for making recommendations and regulations on mass transit. Currently, the standards by which safety on public transit is based on surveys done in the early 1960s, and don't really reflect the way people are built in today's world. From Smart Planet:
So public transit companies are going to have to make some changes (unless people in general make changes to their diet, but that doesn't seem likely). I haven't seen information about Ottawa or Canada, but in time, we're likely going to need to lower the number of people we allow on buses, or make buses bigger. Neither option is without a cost.
The Federal Transit Authority has proposed to raise the assumed average weight of a bus commuter around the United States to accommodate the increasing waistline of most Americans.
The federal agency wants to raise the assumed average weight per bus passenger from 150 pounds to 175 pounds, which could mean fewer people will be allowed to board city buses to meet safety regulations.
The authority has also proposed to add an extra quarter of a square foot of floor space per passenger on buses. With several passengers weighing far more than 200 pounds, the new system seems slightly more realistic.