A new fleet management system run by Zipcar will help Washington D.C. save $6.6 million over five years by getting district government employees to share more vehicles, according to the company.

Zipcar, a company partly owned by the city's transportation director, calls the new system FastFleet, a service for governments. The district is serving as a testing ground for the system, which replaces the district's fleet of 360 vehicles with 58.

Zipcar will equip the cars with global positioning system devices, which will allow the city to better monitor who is driving its cars and where they are going. The city will pay Zipcar a one-time fee of $1,200 a car to install the technology and $115 a month per vehicle to maintain it.

Zipcar (also known as Mobility), which is based in Cambridge, Mass., promotes itself as the largest car-sharing company in the world, with 275,000 members.

The company's Washington D.C. office launched a pilot car sharing program in October with 29 vehicles and four sites. That program saved about $300,000, city officials said. "The one driver-per-car model is broken," said Zipcar Chief Executive Scott Griffith.

The city, not Zipcar, owns the vehicles. Since its fleet was reduced, the city has sold more than 100 cars through Liquidation.com.