NORTH COUNTY - A rustlike substance on the Sprinter's new metal rails is the latest in a string of problems threatening to keep the light-rail line from opening in December, transit officials told the North County Times on Wednesday.

The Sprinter's tight construction schedule called for the entire 22-mile line from Escondido to Oceanside to be ready for testing by Monday. However, trains still aren't moving all the way from Escondido to Oceanside.

When asked about the situation Wednesday, transit district executive director Karen King said workers were trying to iron out kinks in the Sprinter's electrical signaling system.

The district has a few weeks to solve the problem to keep the Sprinter's launch date on schedule, King said, adding that she was confident workers can accomplish that goal.

"If we get to Nov. 1 and we're still not there, then that's a different story," King said.

King said there were delays installing the signaling system that have kept Sprinter trains confined to a relatively short section of track in Escondido and eastern San Marcos.

When rail engineers thought they had all of the system's bugs squashed, she said, a new problem appeared. Workers found that a brown rustlike coating called "mill scale" attached to the Sprinter's steel rails was reducing its ability to conduct electricity.

Project manager Don Bullock said that the Sprinter's $480 million metal rails are a critical component in sending signals to railroad crossing equipment.

"When the train passes over a certain detector in the track, it sends a message to the crossing that tells it to drop the gates and start the bells and all the other things that we have to do when a train is coming," Bullock said. "The (mill) scale was stopping the signals from getting there."

Bullock said the district used wire brushes to remove the scale, but it didn't fix the problem. He said a specialized piece of equipment arrived Tuesday and immediately got to work grinding away the mill scale.

"We've got the equipment for the next four days, and we're going to do as much of the rail as we can," Bullock said.

King said waiting for the equipment had significantly delayed the Sprinter's construction schedule.

"If we could have gotten a grinder here a month ago, we could have gotten past this milestone already," King said.

Signaling has been an problem for the Sprinter in 2007.

In January, the San Diego Association of Governments warned that if the project's contractor did not increase the number of signal workers on the job, the project would not open in December. Designs for signals at some of the crossings also had to be reworked as those crossings were modified.

The Sprinter's original construction schedule called for a three-month period designed to give new train operators, dispatchers and security personnel time to find and fix problems before the first passengers climb aboard.

That time frame has already been significantly reduced and is shrinking daily - a factor that is cause for concern, King said.

"You don't want, on your first day out there, to have the train break down or have a major accident because a signal fails," she said.

However, the transit district chief said she believes the Sprinter will be able to make due with a much shorter testing period and will open in December.

"We won't begin service to the public if we don't believe the service can be operated reliably and safely," King said.

She said the train's operating schedule remains the largest unknown entity between now and opening day. Today, that schedule is only theoretical. Until conductors can begin running east and west on a complete rail line, they will not know whether the proposed schedule of arrivals and departures at each of the 15 stations will work.

"We need to make sure that the trains perform and that the drivers can keep these schedules as they are written," King said. "They need to have as much practice as they can get, and they need time to get to know every inch of the new right of way."

Warren Flateau, a spokesman for the Federal Rail Authority, which governs the nation's rail activity, said Wednesday that there is no prescribed amount of testing time for new rail lines.

"They should take as much time as is necessary to ensure the safe operation of the service," Flateau said.

- Contact staff writer Paul Sisson at (760) 901-4087 or psisson@nctimes.com.