The capacity of Microsoft Corp.'s free Connector regional bus system for employees will more than double under an expansion announced Wednesday. The service, which began in September, will add new routes and expand to a capacity of 4,600 seats a day from the existing 1,800, a company spokesman said in an e-mail.

Microsoft says it's adding seven routes; three Eastside routes begin April 21 and four Seattle routes May 5.

The bus system is one of the amenities the company is using to help recruiting and retention in the face of stiff competition for engineering talent from Google and others. As of November, average ridership was about 55 percent, and about 15 percent of employees who made reservations didn't show.

To date, the Connector system has provided more than 130,000 rides, and it has been used by 4,300 employees, according to the e-mail from Microsoft spokesman Lou Gellos. The company says more than 2,500 of Connector riders had been driving to work alone. It says the system has saved more than 1.3 million pounds of carbon emissions, which Gellos described as the equivalent of turning off electrical power to Microsoft's Building 17, which holds 650 employees, for six months.