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In page Vienna:

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The Vienna metro system consists of five lines (U1, U2, U3, U4, U6) with the U5 currently under construction. The metro currently serves 98 stations and covers a distance of 83.5 kilometers.[1] The services run from 05:00 to about 01:00 with intervals of two to five minutes during the day and up to eight minutes after 20:00. On Friday and Saturday evenings and on evenings before a public holiday they operate a 24-hour service at 15-minute intervals.[citation needed]