Construction on the Rockland Street Bridge likely won’t be finished until December, instead of the original September target, according to state Department of Transportation spokesman Michael Verseckes. The bridge has been closed to traffic since January, and demolition was expected to begin in February. The plan was to rebuild a new bridge on the old foundation, and the project was expected to cost $1.6 million and be complete in the early fall. But construction was halted so the abutments of the bridge could be redesigned when it was discovered that they did not meet modern standards. Verseckes said that the price tag on the project has risen, but said he did not know the revised figure. Construction will resume shortly, said Verseckes, as the abutment problem has been solved. Officials hope to begin demolition this month.