Starting tomorrow, rush-hour subway service will be increased on the Red Line and $1-a-day parking fees will be charged at the Shady Grove station, according to Metro officials.

Trains on the Red Line will run every three minutes during rush hours between the Silver Spring and Grosvenor stations. Trains will operate every six minutes during rush hours between Grosvenor and Shady Grove.

Officials said most Red Line trains will consist of four cars rather than six. Metro recently switched to six-car trains on the Red Line because four-car trains had led to crowding. If crowding occurs under the new schedule, officials said, revisions might be considered.

Trains previously ran every four minutes between Silver Spring and Grosvenor and every eight minutes between Grosvenor and Shady Grove at rush hours. No change is planned in nonrush-hour service.

The $1 parking fees will be collected at Metro's 3,100-space lots at Shady Grove on weekdays from 3 p.m. to 8 p.m. Drivers must pay at exits when they leave. No fee will be charged on weekends or holidays. To encourage ridership, Metro provided free parking for three months after the Shady Grove station opened.