Complex sentence: Until March 31st, 2006, the cards are free to encourage CTA riders to obtain the cards to avoid the fare increase that started on January 1st, 2006, at 6 AM.
Split into simpler sentences: Until March 31st, 2006, the cards are free. They are free to encourage CTA riders to obtain the cards to avoid the fare increase which started on January 1st, 2006, at 6 AM.