[Since this is about a CSX Transportation railroad tunnel, it would seem appropriate to post here]
Washington Post: Aging Baltimore tunnel a threat to shipping economy for the city and Maryland (http://www.washingtonpost.com/local/trafficandcommuting/aging-baltimore-tunnel-a-threat-to-shipping-economy-for-the-city-and-maryland/2012/03/28/gIQAjYCVhS_story.html)
I did find it unfortunate that the reporter did not even mention the other aging tunnel under Baltimore, that being the Baltimore & Potomac ("B&P") Tunnels that were built by the Pennsylvania Railroad and now carry all of Amtrak's N.E. Corridor traffic.
The B&P tunnels carry relatively little freight (NS does have trackage rights for freight), so the height limit is not as much of a problem in terms of double-stack container traffic.