Starting Sunday, the historic green Perley Thomas streetcars will return to service on the entire St. Charles Avenue streetcar route, the Regional Transit Authority announced Saturday.

Since early 2011, streetcars have run only part of the line, with buses carrying passengers the rest of the way between Canal Street and Carrollton as the RTA undertook the task of replacing the decades-old wooden cross-ties that support the streetcar tracks.

The original idea was to do the upriver half of the line, between South Claiborne and Napoleon avenues, followed by the downriver half, from Napoleon Avenue to Canal Street, with the whole project wrapping up by early 2012. Things did not go as forecast.

The contractor hired to handle the $7 million project almost immediately walked off the job, bringing all work to a halt for a few months. Then, once it resumed, the task turned out to take far longer than expected, and the project was split into multiple phases.

The RTA said it has “entered the final phase” of the project, though minor construction and clean-up work will continue throughout the month.

The earliest version of the St. Charles line began operating in 1835. The current vehicles date from the 1920s. The line is listed on the National Register of Historic Places.