More than six months after instituting tougher scheduling guidelines, TriMet has eliminated the "doubleback" shifts that once allowed bus drivers to work up to 22 hours in a 24-hour period to stockpile overtime.

Oregon's largest transit agency changed its work rules after The Oregonian investigated bus and train operators falling asleep on the job with passengers on board. As part of what some workers called a "culture of exhaustion," TriMet regularly allowed drivers to pull repeated marathon shifts on little or no rest, the examination showed.

TriMet negotiated a new deal with Amalgamated Transit Union 757: Bus drivers must now take nine to 10 hours off between shifts, depending on their assignments.

Among other incidents, a veteran Yellow Line MAX operator fell asleep at the controls and crashed a 100-ton train at the end of the line in October 2011. The operator told The Oregonian that he was working with chronic fatigue at the time.

In 2013, TriMet has received only one complaint of a drowsy driver.

On the morning of Oct. 30, a rider reported that a No. 35 bus driver nearly rear-ended a car while repeatedly nodding off on Southwest Macadam Avenue. According to the incident report, the "passenger said each time the driver would pick his head up, squint eyes and shake his head, like he was trying to wake up."

It's impossible to know how many bus collisions are linked to fatigue and long shifts, since TriMet has redacted the names of operators from scores of accident reports due to ongoing discipline, investigations or claims of other personnel exemptions. However, the number of bus crashes this year dropped 16 percent to 403 between January and November, compared to 478 during the same period in 2012, records show.

Meanwhile, TriMet also has made headway on saving on overtime.

After the first eight hours of work during a service day, operators earn time and a half. If they drive on holidays, they make their regular pay plus time and a half.

From June to November, the amount of "unscheduled overtime" paid out by the transit agency -- as opposed to the overtime built into most daily runs -- dropped 20 percent from the same period in 2012, records show.

"We don't know if that is due to the (hours of service) policy change, or the increase in hiring operators," said Mary Fetsch, a TriMet spokeswoman.

Since the beginning of January, when the investigation was published, TriMet has hired 153 operators.

Bruce Hansen, president of Amalgamated Transit Union 757, which represents TriMet's operators and mechanics, said he has heard little grumbling from bus drivers who have lost overtime opportunities. The biggest complaint, he said, is the loss of flexibility in swapping shifts.

Often, he said, drivers can't trade because it would require one of them to violate the new hours of service policy. In some cases, Hansen said, that may pose a safety risk.

"If a driver has worked a week of night shifts and gets reassigned to a garage for early morning shifts starting Monday morning," Hansen said, "he or she can't easily swap with someone to keep working a shift that their body and sleep patterns are used to."

The current hours-of-service policy is only an interim agreement, put in place until permanent guidelines are worked out in ongoing negotiations for a new contract.

"We were forced to do this very quickly," Hansen said. "Does that mean we're going to go back to the way were doing things before? If the union has anything to say about it, no."

-- Joseph Rose

-- Mark Friesen of The Oregonian staff contributed to this report