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.
This week marks the end of the 3rd quarter of 2008. Note that the "Total Traffic" for 2008 (blue line) has been running behind 2007 (green line). If you visit the Railfax web site though, you will find that grain and coal traffic are up this year versus last. Check it out.
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.