If you are thinking of a winter trip to the park, you may be concerned about what the access will be like this winter by snowmobile or snowcoach. Plans that have been tossed about and changed repeatedly in the past decade or more have now been revised once again. The new plan will take effect in the 2014–15 season. During this coming season there will be no change in the daily quotas for the two types of oversnow vehicles.
Having enjoyed four winter trips to the park over the years, I would like to see fewer snowmobiles, but the technology for them has been much improved between my first winter visit in 1988—when West Entrance rangers wore gas masks to protect themselves from the snowmobile exhaust—and my most recent visit in 2012: http://www.yellowstonetreasures.com/nuggets/winter-in-yellowstone-part-1
I disagree with opening the dangerous East Entrance over Sylvan Pass to any access in the winter months, since the expense of keeping it open is unreasonable considering the relatively few people who take advantage of that access.
A complete discussion of the new winter plan can be found at the excellent National Parks Traveler website: