MassDOT advertised the Acton-Maynard section of the trail for construction on September 15, 2015. Six Massachusetts construction companies submitted bids by the February 23, 2016 2:00 PM deadline. The bids ranged from $6,719,972 – $10,445,269. The next step will be the winning bidder selected in April-May and construction starting in June-July. Once construction starts, it will take 24 months to finish.
This new section will end at the South Acton MBTA station. The rebuilt station opened on December 19th and features raised platforms and elevators to cross the new double tracks.
Assabet River Rail Trail's Blog 
When will the Acton section on Sylvia st be open?
Officially, the Acton section won’t be finished until spring 2018. But the Acton paving is estimated to be done in 10 days, including the Sylvia Street access.