Frequent flight delays, often caused by weather or congestion, have also played a role in the switch from planes to trains. Amtrak arrives on time 90 percent or more of the time, according to its data. Delta said the shuttle’s on-time percentage was “in the mid-80s,” and US Airways said its record was a little higher.

The Acela has played a big role in attracting passengers in the Northeast. The trains averaged about 80 percent full and earned an operating profit of more than $200 million last year on nearly $500 million in revenue.

But Acela tickets can be costly and wireless service spotty, and Amtrak just added a cancellation fee policy for all of its trains. Acela fares between New York and Washington range from an average of $145 for regular business class to $351 for first class; New York to Boston, $104 to $251; and Boston to Washington, $163 to $393.

Non-Acela train fares between New York and Washington average $49 to $153 for coach and $120 to $193 for business class; New York to Boston, $49 to $133 for coach and $104 to $168 for business; and Boston to Washington, $70 to $185 for coach and $144 to $233 for business class.

At US Airways, the lowest one-way coach rate between Washington and New York was $236 as of Wednesday, and the lowest first-class fare $335, before taxes and fees. Between New York and Boston, the fares are $229 and $314, and Washington-Boston, $62 and $369. Corporate and other kinds of discounts can lower the prices.

To accommodate demand, Amtrak wants to add cars to each of the 20 Acela trains now in its schedules, increasing Acela capacity 40 percent, the railroad said, or about 124 seats per train. Amtrak plans to add the new cars by 2015 and to increase the frequency of the trains between New York and Washington by 2020.

But the bigger Acela trains will solve only part of the problem.

The railroad spends about $350 million a year to keep bridges, tunnels and rails in working condition, said Drew Galloway, chief of Northeast Corridor planning and performance for Amtrak. It has replaced some older bridges, like the 100-year-old Niantic River bridge in Connecticut, so trains can operate at greater speeds.