An upcoming signal replacement project on the MBTA’s Red Line will cause weekend train shut-downs in July and August — starting this weekend— between the JFK/UMass and Ashmont stations.

The diversions will begin at the end of service starting this Friday night and last until 4 a.m. on Monday during two July weekends (July 14-16 and July 21-23) and two August weekends (Aug.4-6 and Aug. 11-13). During these diversions, Savin Hill Station, Fields Corner Station and Shawmut Station will all be closed and busses will runalong Dorchester Ave. between Ashmont Station and JFK/UMass Station.

Passengers will still be able to board Braintree trains going to Alewife Station at JFK/UMass.

The MBTA’s Columbia Junction Signal System Replacement project will involve the replacement of antiquated equipment in the area of the JFK/UMass Station and the installation of fiber optic cable between JFK/UMass and Ashmont stations.

“Once the project is completed, T riders will see an improvement in service reliability,” MBTA Communications Director Joe Pesaturo said in an email.

Weekends were chosen as the most opportune time since ridership is lowest during these times and the time span would provide the contractor ample time needed to complete the project. According to statistics provided by Pesaturo, on an average Saturday about 3,975 people enter Ashmont Station, with this number dropping to 2,455 on an average Sunday. The next most trafficked station in this area is Fields Corner, with an average of 2,635 passengers on Saturdays and 1,940 on Sundays.

No problems are expected by the MBTA because of the weekend diversion, and both Ashmont and JFK/UMass Stations will be staffed by MBTA officials who will be available to assist customers and answer any questions, Pesaturo said.

The MBTA says riders allow 15 minutes extra travel time due to the shuttle.