The New York Times reports that “Amtrak Dominates Northeast Corridor Travel.” That’s absolutely true–as long as you don’t count buses. Or cars. Or intermediate points between Boston, New York, and Washington.
The Times says that Amtrak has a 75 percent share of the “air/rail” market between Washington and New York, but it only has a 54 percent share of the “air/rail” market between New York and Boston. It doesn’t say anything about intermediate points.
In a more realistic assessment, page 4 of Amtrak’s 2010 Vision for the Northeast Corridor reports that Amtrak carries 6 percent of travel in the Northeast Corridor, while planes carry 5 percent and the remaining 89 percent goes by highway. Amtrak doesn’t break out bus travel, but I estimate buses carry significantly more passengers than Amtrak, or approximately 8 to 9 percent of the corridor market.