SL has a common ticket system in the entire Stockholm County, which allows for easy travel between different modes of transport. The tickets are of two main types, single ticket and travel cards, both allowing for unlimited travel with SL in the entire Stockholm County for the duration of the ticket validity. On 1 April 2007, a zone system (A, B, C) and price system was introduced. Single tickets were available in forms of cash ticket, individual unit pre-paid tickets, pre-paid ticket slips of 8, sms-ticket and machine ticket. Cash tickets bought at the point of travel were the most expensive and pre-paid tickets slips of 8 are the cheapest. A single ticket costs 32 SEK with the card and 45 SEK without and is valid for 75 minutes. The duration of the travel card validity depended on the exact type; they were available from 24 hours up to a year. As of 2018, a 30-day card costs 860 SEK. Tickets of all these types were available with reduced prices for students and persons under 20 and over 65 years of age. On 9 January 2017, the zone system was removed, and the cost of the tickets was increased.