Amtrak Guest Rewards is running a winter promotion on Acela. Register for the Great Escape promotion and for every three roundtrips (or six one-way trips) you take on Acela through March 19, 2011, you’ll receive one free roundtrip on Acela that can be redeemed for travel between July 3 and Aug. 31, 2011. A minimum spend of $85 is required per qualifying one-way trip or $170 roundtrip. Free award trips are subject to Acela award restrictions on weekdays and members redeeming their free trips are not allowed to travel between the start-of-service and 8:59am, or between 2:00pm and 5:59pm on Monday through Friday. Free trips can be booked starting June 1, 2011 on amtrakguestrewards.com or by calling (800) 307-5000.

Members can earn up to two roundtrips and the free roundtrips will be awarded as two one-way trips.

Bottom line: Buy three, get one free is a good bonus, but be aware that there are restrictions on when you can travel on the award ticket during the week and the cheapest fares you can find aren’t eligible for the three required trips. But if you can find fares at the minimum of $170 roundtrip, getting a free trip works out to about a 33 percent discount.