"It was the 'hell train' that did it," he said. "They didn't like the bad publicity, and they didn't want to lose the contract."

Taylor said this was the first year in which MARC had access to all 26 locomotives in the new diesel fleet that the MTA ordered in early 2008 at a cost of nearly $90 million. There was hope at the time that the new fleet could significantly improve service in 2010, but a slow delivery schedule and a dispute over safety certification delayed their full impact until this year.

But now the MTA is pleased with its acquisition. Taylor said the new diesel engines have held up well to the rigors of operating in Maryland and have allowed MARC to reduce its dependence on the more powerful, but more breakdown-prone, electric engines on the Penn Line.

The Penn Line improvements came despite serious weather problems this summer, including stretches of 100-plus-degree days in June and July. MARC even posted a small gain on the line in August: a 91 percent on-time rate despite an earthquake and Hurricane Irene. That month, according to MTA records, 51 percent of the delays were weather-related, compared with only 7 percent chalked up to mechanical failures.

In September, a month in which MARC usually improves from the torrid summer months, Penn Line trains met their schedule 98 percent of the time. The percentage of delays caused by mechanical problems plummeted to 8 percent from 53 percent in September 2010.

MARC and Amtrak will make further tweaks to the Penn Line schedule in November in an attempt to improve service. Taylor said MARC's big push over this winter will be to improve service on the Brunswick Line.

Guroian said the big problem on the Penn Line now is overcrowding. Another is that the trains don't travel quite as fast when pulled by the new diesel engines, compared with the electric locomotives.

But most MARC riders can live with those problems if the trains run on time, he said. "The predictability in the MARC system is the No. 1 concern."

The crowding, he noted, is a sign of the MARC's growing ridership.

"It's a testament to the fact that people in Maryland need a commuter service and they need it more than they ever have," he said.