PETALUMA – The Sonoma Marin Area Rail Transit District is expected to consolidate its administrative operations to a new Petaluma headquarters in the third week of September, a move that General Manager Farhad Mansourian said would begin with the transit agency’s Santa Rosa project office at 490 Mendocino Ave, Ste. 102.

A second office, at 750 Lindaro Street, Ste. 200 in San Rafael, will move to the new headquarters in October, he said. Operations are expected to begin at the Petaluma site, at 5401 Old Redwood Hwy., by late September.

The SMART Board of Directors authorized a six-year lease with San Mateo-based Cornerstone Properties in June. The 25,000-square-foot, second-floor space was leased at approximately $510,000 per year with a 3 percent annual escalation.

Work is currently under way to improve internet capacity and other features at the location. Long-term plans could include up to 100 workers at the site, including consultants and more than 70 staff members.

The office will also include backup systems for the dispatch and operations center that will be constructed as part of a maintenance center on a 5.5-acre parcel at 1210 Airport Blvd. in Santa Rosa, purchased in April for $2.7 million.

Construction is ongoing for the commuter rail system, with the initial 38.5-mile operating segment is expected to be operational between Santa Rosa and San Rafael by late 2015 or early 2016. Workers are currently improving railroad crossings and track, starting from the north end of the segment.

Total cost to before the segment becomes operational is expected to be between $360 million and $366 million. When further funding is available, the transit district plans to extend the line north to Cloverdale and south to Larkspur, for a total length of 70 miles.