A recently activated collision-avoidance system for SEPTA subway-surface trolleys has created chronic rush-hour delays for riders, despite $25 million and much of a decade spent trying to work out the flaws.

The "communications-based train control" system was designed to prevent rear-end collisions by automatically controlling trolleys as they travel underground on their way to and from West Philadelphia.

But the system has slowed the cars too often and sometimes has backed up trolleys five or six deep at the West Philadelphia entrances to the 2 1/2-mile tunnel.

"Almost every other day, I'm late for class," said William Blue, waiting for a Route 11 trolley under City Hall. He commutes from West Philadelphia to computer classes in North Philadelphia. "We're always getting stuck in the tunnel and delayed. It will just suddenly come to a halt."

"In the last two weeks, it's been worse," Dottie Farrell said Monday as she sat on a Route 13 trolley stuck in the tunnel near City Hall. Farrell, of Upper Darby, works at Independence Blue Cross in Center City and was trying to get to 30th Street. "I should have walked to 15th Street."

On one stranded Route 13 trolley last week, the operator handed out paper transfers and directed passengers to go catch a bus. Other arriving passengers made it halfway down the stairs to the trolley station, saw the line of waiting trolley cars, and headed back up to the street.

Mayor Nutter's transportation officials complained to SEPTA last week about the delays, and this week the control system's manufacturer, Bombardier Inc. of Montreal, will be back in Philadelphia to try to fix it.

"We're still having failures several times a day. It's too much," said Patrick Nowakowski, SEPTA's assistant general manager in charge of operations.

The heart of the problem is that the automatic control system cannot keep up with the rapid arrival and departure of trolleys during peak hours, when a trolley arrives about every 50 seconds.

"Look at that. It's brake and go, brake and go," a frustrated trolley driver said last week, pointing to a red light on his instrument panel. Each time the light came on, he had two seconds to slow the trolley or an automatic brake would kick in.

Operators complain that trolleys are routinely 30 minutes to an hour behind schedule during peak periods, and they blame the control system. They say they made much better time with the old-fashioned wayside signal lights and manual braking.

Five Green Line subway-surface routes carry about 90,000 riders a day, converging on the tunnel at two portals in West Philadelphia. The five routes use 112 electric trolleys, which run at street level under manual control after they leave the tunnel.

After about four years of design and installation, SEPTA put the automatic system into part-time operation in the tunnel in May 2005. Because of continuing rush-hour problems, though, SEPTA kept using the manual system during peak hours for three years.

That ended after 11 people suffered minor injuries July 22 when a trolley ran into the back of a stationary trolley at the 13th Street station and knocked it into a third stopped trolley.

It was the kind of accident the automatic system was created to avoid, and SEPTA officials decided to put the system into full-time operation.

"It's a difficult balancing act" between safety and speed, Nowakowski said. He said SEPTA had averaged about two trolley collisions a year.

Most of the nearly $25 million for the system has been borne by Bombardier, which agreed to install it as compensation for mistakes made in producing cars for the Market-Frankford El in the 1990s.

Because Market-Frankford cars came in late and overweight, SEPTA negotiated to receive the trolley control system in lieu of a cash settlement from Bombardier.

The transit agency is still trying to get its money's worth, and has now spent several million dollars of its own on the project.

Despite complaints from operators, passengers and city officials, SEPTA said it needed to keep operating the control system to fix it.

"You've got to see the bugs so you can deal with them," Nowakowski said. "We can't find these problems if we don't turn it on full time."

The system is a complex combination of computers, radio-frequency tags and electronic transponders that is supposed to calculate the location and speed of each car and keep it a safe distance from other trolleys.

Similar systems have worked well in light rail at airports and on transit lines with less-frequent service. But the electronic brains have not been able to cope with the frequent headways of SEPTA trolleys (and today's headways are slower than those of 40 years ago, when rush-hour trolleys ran every 24 seconds).

When the system automatically slows cars to 20 m.p.h. or when it can't promptly identify a car leaving or entering the tunnel, backups quickly develop. And when a car breaks down, the control system exacerbates delays as SEPTA tries to get trolleys back on schedule.

For riders, the delays are an almost-daily annoyance.

"There's no rhyme or reason to it," said Temple student Tania Stead, waiting for a Route 34 trolley. "If it was consistent, you could plan ahead and find another way to go. But you never know when it's going to happen."

Contact staff writer Paul Nussbaum at 215-854-4587 or pnussbaum@phillynews.com.