A CNN investigation found that Greyhound has not been enforcing a rule designed to keep bus drivers alert and passengers safe.

Greyhound documents show that drivers are told to take breaks every 150 miles. But CNN found that the rule is more of a guideline than a mandate. Greyhound has no way of forcing its drivers to stop, and the company has many routes with no required stops for more than 150 miles.  

In a deposition obtained by CNN, the company’s CEO said that Greyhound relies on drivers to use their best judgment. If they’re too tired to drive, he said, they have an obligation to speak up.

Greyhound is the largest bus company in North America. Eighteen million people use the busses every year, traveling about 5.5 billion miles.