Metro officials say few riders are claiming the $3 rebates being offered to those who buy SmarTrip cards.
Since the transit agency started offering the incentive back in September, only one out of four riders have taken advantage of the deal.
Metro officials say one possibility is that most riders already have SmarTrip cards, and recent purchases may have been made by those who rarely use the system or are simply visiting the area. Another theory is that some riders might be forgetting to claim the rebate or aren't aware of it.
The incentive was Metro's way to get customers to make the switch from paper fare cards the plastic during the final four months of 2012. More than 350,000 people made the switch, but just 67,000 riders have claimed the $3 rebate.
To get the rebate, the card has to be registered online and the rebate is added five days after it is used. However, it has to be claimed within 30 days at a station used in the past 20 days.