Service returned to normal yesterday on Metro's Red Line after a derailed train that caused delays was removed.

Metro officials said they remain confounded about what caused the six-car train to come off the tracks at the Silver Spring Station on Thursday afternoon. Initial inspections did not reveal any obvious causes, officials said, and a more thorough investigation will continue into next week.

"I'll be working through the weekend putting the data together," said Steven Feil, Metro's chief operating officer for rail.

The train derailed while making a routine turnaround on a secondary track at Silver Spring, slamming to a stop four to six feet from the main line. No passengers were on the train when it derailed, and no one was hurt in the incident.

Metro officials said the train was put back on the rails at 4:30 a.m. yesterday. Officials said the train's rear four cars left the station under their own power and returned to regular service. The two front cars left under their own power later in the day and went to a yard for further investigation, officials said.

Outbound Red Line train service terminates at Silver Spring or at Glenmont, which is the end of the line in eastern Montgomery County. The trains turn around and head back toward the District and on to either Grosvenor-Strathmore or Shady Grove, in the western part of Montgomery.

Because the turnaround area at the Silver Spring Station was blocked by the disabled train for most of yesterday, the trains that normally terminate there instead turned around one stop north, at the Forest Glen Station. Metro officials said Red Line service was minimally affected by the alteration.

But officials said service was slow in the early morning hours, especially between 5:30 and 6:15, because regular preparations on the line were slowed by the work on the derailed train.

The derailment was the third in two years for Metro and the latest setback for the transit system. This summer, a 20-by-20-foot section of ceiling crashed on the mezzanine area at Farragut North, heavy rains that flooded the Silver Spring Station slowed service for nine days, and a train operator and two passengers were stranded for at least a half-hour outside the Forest Glen Station when communication systems were knocked out during a storm.

Metro officials have said repeatedly that the system needs $1.5 billion in the next six years to buy rail cars and buses and to rehabilitate stations and equipment. Officials released a plan Thursday that calls on local governments to markedly increase Metro funding to pay for their needs. So far, government officials have reacted coolly to suggestions that they increase their contributions.

Metro is the only major transit system in the country without a dedicated source of funding and must go hat in hand to local governments each year in search of funds.

A Metro train blocks the Silver Spring Station turnaround area, which forced trains that usually turn there to turn around at Forest Glen.