in the 1970s, the letter A was designated to a stopping train to Kirkkonummi station. Limited-stop train to Kauklahti The E train has been in operation since 1974, originally as a stopping train terminating at Espoo station. In 2007, the service was extended one stop further to Kauklahti station. Stopping train to Kirkkonummi The L train is one of only three services which have remained unchanged since the alphabetical services were introduced in 1972. It operates exclusively in the fringe hours and is the only Coastal Line service to run hourly through the night on weekends. Limited-stop train to Kirkkonummi The U train was instated in 1988 as a rush hour express service, becoming an all-day service in 2002 after the Leppävaara Urban Line was completed and capacity grew. In 2016, remaining services of the S train were merged into the U which then became a trunk service with 30 minute intervals. Limited-stop train to Siuntio The X train first came to existence as one daily back-and-forth service to Kirkkonummi, in operation between 2016 and 2018. The X was reinstated in 2020 as the identifier for limited-stop trains to Siuntio station, formerly operated as exceptional services of the U train. Before being instated on the Coastal Line in 2016, the letter X had been used unofficially by railway staff to designate a letter-lacking service to Riihimäki station on the Main Line. Express train to Siuntio The Y train is the fastest westbound service on the system, calling only at seven stations out of the 18 on its route. The terminus of the Y has changed quite often in the 2000s, currently terminating at Siuntio station since 2016 after Karis station was excluded entirely from the commuter rail network. Ring Rail Line Anti-clockwise stopping train to Helsinki Airport and back to Helsinki Central Clockwise stopping train to Helsinki Airport and back to Helsinki Central The I & P trains are commuter services running in opposite directions and calling at all stations. These services were instated in their current forms in 2015, after the completion of the Ring Rail Line, and have run on 10 to 20 minute intervals throughout the day ever since. The I and the P also cover the initial stretch of the Main Line and the entire Vantaankoski Line. Main Line Express train to Hämeenlinna The D train is a single return service operated on weekdays. It departs