From Boston and Callahan Tunnel: Exit Callahan Tunnel and stay in the left lane. This will lead you past Logan Airport to Route 1A, North. Continue on 1A to the first traffic light. Turn left at that light and follow signs to Park, Shuttle & Fly.
From Route 95 And Route 1 (North Of Boston): Follow Route 1 South through Saugus and into Revere. Exit Route 1 near the Showcase Cinema and take the third right off the circle. That is Route 60 East. Follow Route 60 East until it joins Route 1A. Follow Route 1A South past Suffolk Downs Race Track.
Take first right after the race track and follow signs to Park, Shuttle & Fly.
From Mass Pike: Go to the end of the Mass Pike to downtown Boston. From the Ted Williams Tunnel follow signs onto Rte 1A North. On Rt 1A get in your left lane, and take the left at the traffic light (after the Holiday Inn). Follow signs into the lot.
Have used this service at the Intercontinental many times and love it. Covered parking. Very frequent comfortable luxury shuttles to the L and airport every 15 minutes. Easy process and very courteous staff. Also, you walk right by the very nice hotel restrooms when you come off the elevator.
Most helpful critical review
If I am paying to park my car in the garage, I should not have to take a cab to make my plane on time because during peak times the shuttle only runs every 30 minutes which is quite ridiculous.