It was found—in cities like Paris and Copenhagen—that to have a major impact there had to be a high density of available bikes. Copenhagen has 2500 bikes which cannot be used outside the zone of the city centre (a fine of DKr 1000 applies to any user taking bikes across the canal bridges around the periphery). Since Paris's Vélib' programme operates with an increasing fee past the free first half-hour, users have a strong disincentive to take the bicycles out of the city centre. The distance between stations is only in inner city areas.