Complex sentence: SmarTrip was the first contact-less smart card for transit in the United States when WMATA began selling SmarTrip cards on May 18,1999, and by 2004,650,000 SmarTrip cards were in circulation.
Split into simpler sentences: SmarTrip was the first contact-less smart card for transit in the United States when WMATA began selling SmarTrip cards on May 18,1999. By 2004,650,000 SmarTrip cards were in circulation.