 To allow the introduction of low-floor trains without having to demolish existing high platforms, the network was divided into two sub-networks of different floor heights.On weekdays, all lines are served in 5- to 10-minute intervals from 6 am to 8 pm, with little or no service between around 1 am and about 4.30 am, and usually 15-minute intervals in the early night and early morning.On weekends, there is an hourly service throughout the night.