towards Helsinki in the morning and returns to Hämeenlinna station in the afternoon, calling at only eight stations on its route. The service was introduced in 2016, terminating at Hämeenlinna. For a while in 2016 and 2017, the D was the only northbound commuter service to skip Tikkurila station. Stopping train to Kerava The K train has terminated at Kerava station ever since its introduction in 1972 but has gradually shifted from an express service to a stopping train, now calling at all stations. Historically, the K had a counterpart stopping at all stations known as the N train. Before finally being merged to the K in 2019, the N was limited to fringe hours and weekend nights. Limited-stop train to Riihimäki / on certain departures to Tampere C The R train is the Main Line's main commuter service. It has two termini – Riihimäki station every half an hour and Tampere Central every two hours. Before Kerava station, the R only calls at major interchanges Pasila and Tikkurila, calling at every station thereafter. Often heavily crowded during peak hours, especially in the HSL region, most R departures are operated with up to four Class Sm4 units. Stopping train to Riihimäki The T train is an hourly night time service, calling at all stations on the way to Riihimäki. It is the only regular train service in Finland to operate throughout the night on weekdays. Lahti Line Limited-stop train to Lahti / on certain departures to Kouvola The Z train is an hourly service on the Lahti Line, inaugurated in 2006 after the new line was completed. Previously, the most straightforward way to Lahti went via Riihimäki station. Certain fringe hour departures are operated all the way to Kouvola station whilst calling at all stations in between. The extended Z route from Helsinki to Kouvola is the longest haul on the entire VR commuter rail network. The Z was the first Finnish commuter service to regularly require rolling stock capable of running at a speed of 160 km/h. Schematic map of services Note that commuter services G, M and O are not part of the Helsinki commuter rail network. Former services Some discontinued letters have since been redesignated to new services on different lines and routes. For the purposes of distinction and clarity, symbols of former Helsinki commuter rail services are colored grey on Wikipedia, regardless of their actual color