http://railfax.transmatch.com/
Here is an example of the information available on this web site. This graph shows Total Traffic for 2008-2009 vs. 2007-2008. There are more graphs and tables on the web site showing data by railroad and by commodity.
Also check out our post on Monday, 3/16/09, titled Railroads Could Telegraph Rebound.
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.