Ticket machines operate at every Luas stop and these are the only source of single-journey and return tickets. They also sell 1-day, 7-day and 30-day tickets, valid in either some or all the fare zones, for adults, children and students. It is also possible to purchase 'Combi' tickets valid on Dublin Bus and Luas. DART and Luas 'Combi' tickets have been produced since Luas opened but despite this being a major ticket option these Luas-DART Combis are not available at either ticket newsagents or online from either Iarnród Éireann or Luas, nor are they available in Luas vending machines. They are available only from Iarnród Éireann ticket offices. Transport user lobby groups like 'Rail Users Ireland' have written to both Luas and Iarnród Éireann asking for an explanation for this and none has been forthcoming. While it is also possible to purchase Luas-DART-Dublin Bus 'triple combi' tickets (from Iarnród Éireann booking offices) from monthly ramblers upward, these are often more expensive than simply topping up a Leap Card to its weekly cap rate (currently €40 for Adults). Certain ticket combinations are not possible (for example a one-day student ticket), and tickets can only be valid from the stop at which they are purchased and must commence their validity within 90 minutes, valid until a specific time shown on the card. Certain tickets require the user to hold an ID card and write the number on the ticket, to prevent the ticket from being transferred to another person. Ticket machines accept card payments (by American Express, Laser, MasterCard, or Visa and have a weekly limit of €150 (upper limit changed from €50 per transaction to €150 per week in January 2012 after upgrading all POS terminals to have a PIN keypad). Formerly €5 was the minimum amount which could be paid via card, but this limit has since been removed. Like other Irish transport operators, Luas has taken to requiring students to purchase a special Student Travelcard, not recognising their student cards as enough to get a discount. These have been merged with the Leap Cards to form a personalised orange Leap Card with new benefits such as lower daily caps.