In Alexandria, where bicycle commuting is already well-established, the City Council agreed unanimously Tuesday night to join Capital Bikeshare, adding a third city to the regional network.

The city, with its brick-and-cobblestone streets, will install six stations, with 54 bikes, in the Old Town and Carlyle neighborhoods. If successful, the program would expand to Del Ray, Arlandria, Potomac Yard and the West End, later connecting to the Arlington network. The earliest that the bright-red bikes will be stationed in Old Town will be spring 2012, city officials said.

Council members were inundated with calls and e-mails lobbying them to approve the measure, “probably the most e-mails I’ve ever gotten in an hour,” Mayor William D. Euille (D) said.

Tourists are expected to be prime customers, but local residents out for a quick errand or commute also are targets.

“We have a higher share of bike ridership for commuting to work than Arlington has,” council member Rob Krupicka (D) said last month when the idea was raised to the council. “The Eisenhower Valley to the east, and West End is where this pent-up demand for non-car transportation is.”

When the network was launched in Washington and Arlington 11 months ago, with 1,100 bikes at 110 stations, officials expected 6,000 people to buy the $75 annual membership within the first year. Instead, that benchmark was reached in six months, then doubled when the network offered a half-price promotion. Capital Bikeshare now claims 70,000 daily and weekly memberships (costing $5 or $15, respectively) and 15,000 annual memberships, generating 1 million rides.

Alexandria expects similar success. Between 40,000 and 50,000 bike trips are expected in the first year, which officials think will eliminate hundreds or thousands of single-occupancy car trips.

The cost of setting up and operating the network the first year would be covered by $400,000 in federal transportation funds, and revenues from the rental bikes are expected to help defray most of the cost of the program the second year, as has been the case in the District and Arlington. In addition, some Alexandria employers are asking about covering the capital and operating costs of a station in exchange for promotion.

For users, the first 30 minutes of every ride is free, and daily memberships can be purchased at any station, while longer memberships can be bought online or by phone. A rider could pick up a bike in Old Town and travel to downtown Washington, leaving it at any Capital Bikeshare station.

City staff said if the council approves the proposals, they would coordinate with citizens’ groups and other stakeholders to determine where the bike stations would be placed, most likely on city or Washington Metropolitan Transportation Authority property. More than 30 individuals and groups have contacted the council to ask the city to join the network.