Holiday shoppers visit product shipping sites like clockwork, even though online retailers have extended their shipping dates to accommodate procrastinators, and the amount of traffic on shipping Web sites has risen, according to Hitwise.

The Tuesday and Wednesday before Christmas have continued as the peak days for the highest number of visits for shopping and shipping Web sites, according to Hitwise. The online intelligence company reported a 12% increase in traffic to shipping sites like Federal Express, UPS, and DHL on that Tuesday compared with the same day last year and a 17% increase on the Wednesday before Christmas this year, also compared with the same day last year.

Web sites in the shopping and classifieds category drove most traffic to shipping Web sites, while e-mail and search engines followed as the main drivers. Sites that offer shopping and classifieds sent 27% of the traffic to shipping Web sites for the week ending Dec. 15, while e-mail referred 26% of the visits and search engines drove 15% of the traffic to shipping sites, according to Heather Dougherty, director of research at Hitwise.

Dougherty found that most traffic to shipping Web sites comes from retailers' Web sites or e-mail confirmations. Dougherty said although online retailers have simplified systems for tracking packages, some have retained barriers -- like account login requirements -- which take time and may discourage shoppers.

She said e-mail messages notifying buyers that their shipments have been sent generate traffic from consumers eager to track their packages. She said that Yahoo Mail drove most of those visits to shipping sites (15%), while Windows Live Mail drove 7% of the visits in mid-December.