Speed restriction on curve in Revere, MA

On the Eastern Route, as the line goes through Revere, the tracks curve as they go under Revere Beach Parkway (going inbound, this curve immediately precedes the long straightaway to Eastern Avenue, in Chelsea). In any case, I believe that trains have been restricted to 65 MPH as they go around this curve - if I am correct, does anyone know why this speed restriction was implemented? As I recall, trains used to travel at 70 MPH around this curve.