As of Earth Day 2011, the company owns 350.
To celebrate Earth Day and the three-year anniversary of its green fleet, Discount Cab will attempt to best its own record of taxi trips dispatched in a day. Additionally, the company will donate $1 from every ride to the Phoenix-area nonprofit Homeward Bound, which assists families struggling with homelessness and domestic violence.
Craig Hughes, CEO of Discount Cab parent company Total Transit, said the Prii have proved a boon.
"We found real acceptance from both our passengers and our drivers with the Prius platform," said Hughes in a press release. "We've been blown away by not only the durability of the cars but also the positive response we've received from customers."
"We're averaging more than 10,000 trips per day during a period when many taxicab companies are losing business," he said.
The company's customer base has grown 30 percent a year since it added the Prii.
In addition to its green fleet, Discount Cab boasts a green headquarters. Last year the company installed 400 solar panels, which provide 25 percent of the building's power.