http://railfax.transmatch.com/
Here is an example of the information available on this web site. This graph shows Total Traffic for 2007-2008 vs. 2006-2007. There are more graphs and tables on the web site showing data by railroad and by commodity.
Note: This web site has new tables and graphs every Thursday. So, if I am late or miss a week with this blog posting, you can check for new data on Thursdays.