Keeping the Northern Transcon open during the winter is a significant challenge, whether from snow in the Midwest and mountains, or rain in the Pacific Northwest. Heavy rains have the potential to cause mudslides along Puget Sound between Seattle and Everett and in the Nisqually, Washington area between Tacoma and Olympia. For example, in early January 2006, there were four slides between Seattle and Everett. In late January 2006 and again in early February 2006, mudslides occurred both between Seattle and Everett and around Nisqually. Heavy snow in the Rockies around Marias Pass have the potential to cause avalanches that can block the tracks. Following the clearing of a slide or an avalanche, no passenger train can run on the track for 48 hours to ensure that the slide area has stabilized, per BNSF policy.