Airplanes are getting stuck in lots of traffic jams this summer, but Amtrak is on a roll.

Ridership on the passenger rail system is up 6 percent so far this year, the biggest jump since the late 1970s. On the Acela Express, trains that run at higher speeds between Washington and Boston by way of New York, the number of riders has surged 20 percent over the past 10 months. That’s enough new passengers to fill 2,000 Boeing 757 jets.

Richard Rosen, who heads a pharmacy-fulfillment company in Boston, is making as many of his trips to New York as possible on the Acela.

Flying to New York, with traffic to and from La Guardia Airport, flight delays and security lines, has become “an absolute horror show,” he says. A recent one-hour flight turned into four hours of exasperation. Rosen says the Acela, which takes about 3½ hours to get from Boston’s Back Bay Station to Pennsylvania Station in midtown Manhattan, is more comfortable and reliable. “The train is much better, and you can do your work and use your cell phone during the whole trip,” he says.

While airlines are running later and with more delays than ever — a third of flights arrived late at La Guardia Airport between June 1 and Aug. 15, according to Flightstats.com — Acela’s performance is improving. The train is running on time 88 percent of the time, so far this year — up from 84 percent a year ago. It was 90 percent on time in June. With Amtrak selling every seat on some Acela trains in peak travel periods, Amtrak recently added another weekday Acela roundtrip between New York and Washington to keep up with growing demand. The new train dropped all but one stop, Philadelphia, shaving 15 minutes off the normal 2¾-hour, five-stop New York-Washington trip.

All this represents a big change for Amtrak, the perennial Rodney Dangerfield of passenger transportation, which has faced scathing criticism in recent years for late trains and poor service. The Bush administration has in recent years tried to cut or eliminate its federal subsidies, which total $1.3 billion in 2007. And allies of the White House remain harsh critics. “Amtrak still needs to change its way of doing business,” says Joseph Boardman, the Bush administration’s top rail official as head of the Federal Railroad Administration and an Amtrak board member.

The Bush administration has repeatedly called for an overhaul that would turn over Amtrak’s Washington-New York-Boston Northeast Corridor to the states along the route. Amtrak would become a pure passenger rail operating company that would then compete for state contracts to provide intercity service. The administration plan would create a long-term partnership where states determine passenger rail needs and the federal government provides matching funds similar to highways and transit.

But Amtrak’s success lately isn’t confined to the Northeast. While the railroad’s long-distance trains continue to suffer from lengthy delays, its ridership is up sharply on some improved state-supported corridors, including Chicago-St. Louis, up 53 percent in the 10 months through July.

The improved service is being noticed by Amtrak’s supporters in Congress and helping tilt the odds in the railroad’s favor on more money for future improvements.

“This means a lot of goodwill in the bank for Amtrak among policymakers for increasing its funds and expanding service,” says Rep. James Oberstar, a Democrat from Minnesota, who heads the House transportation committee. “The dynamics have shifted in favor of a strong future for Amtrak.”

The House recently passed a fiscal 2008 funding bill with $1.4 billion for Amtrak plus $50 million to match state financing of capital projects. The Senate is considering Amtrak funding of $1.37 billion plus $100 million for the capital program.

Airlines, of course, have their own ideas of how best to improve travel in the Northeast. Many of them are actively supporting a federal government proposal to replace the current air-traffic-control system with a more modern one that allows more flights. The Next Generation ATC system is estimated to cost nearly $40 billion and take until 2025 to be fully implemented, says the Air Transport Association.

“If that is taken care of, a lot of the problems we have today will be eliminated,” says a spokesman for US Airways Group Inc., of Tempe, Ariz., which operates one of the two hourly air-shuttle services between Washington, New York and Boston. A spokeswoman for JetBlue Airways Corp., of Forest Hills, N.Y., says it’s wrong for tax dollars to be used to subsidize Amtrak passenger trains “when a modernized air-traffic-control system is not yet in place or even funded.”

But some big names in the airline industry are supporting Amtrak by calling for the United States to do what governments in Europe and Asia have long done — building high-speed train lines for short-distance travelers and freeing up runway space for long-distance flights.

“You have to begin to put the infrastructure in place to put in high-speed trains,” says Gordon Bethune, who retired in 2004 as chief executive of Continental Airlines Inc. “It should be a national priority. If the French can do it, why can’t we?”

Another airline-industry legend, Robert Crandall, former chief executive officer of American Airlines parent AMR Corp., says improvements to Amtrak’s network in the Northeast is one of the best ways to reduce aviation gridlock.

Since Amtrak introduced higher speed Acela trains in 2000, the railroad’s share of the 10,000 daily plane or train passengers traveling between Washington and New York has grown to 54 percent from 45 percent. The Acela runs as fast as 135 miles an hour in some places between New York and Washington. It reaches its top 150-mph speed on a small part of the route between New York and Boston. Amtrak’s share of the Boston-New York air-rail market is also up, but by a lower amount.

Chris Gremski, who manages travel for the New York-based Open Society Institute, investor George Soros’s charitable foundation, says a significant number of the foundation’s employees have switched to Acela from air shuttles between New York and Washington. Airport security lines and flight delays are wiping out the time savings of the plane, he says, and Acela is cheaper (the one-way nondiscounted fare for the New York-Washington Acela is $199, compared with $324 for the air shuttle).

Gremski says some employees also are using the train because they think it is more fuel-efficient and less polluting than the plane.

But there are definite limits to how much more Acela can do. Alex Kummant, Amtrak’s president and CEO, said in a presentation recently that Amtrak is constrained by the size of the Acela fleet, which numbers 20 trains. If he had his druthers, Kummant said, Amtrak would be able to add cars to Acela trains to meet demand, rather than being limited to 304 passengers by Acela’s fixed complement of six cars and two locomotives.

Acela will never clock the steady 180-mph speeds reached by the fastest European and Japanese trains as they travel on dedicated tracks from city to city. On the Northeast Corridor, Acela is stuck with curvy tracks that it must share with freight and commuter trains. Space for more and faster trains is particularly limited in New York, where the Northeast Corridor squeezes down to just two tracks under the Hudson River.

Still, for $625 million in upgrades to tracks, equipment, signals and electrical power systems, Amtrak could shave 15 minutes from the Acela’s schedule between New York and Washington, Kummant told Congress last month. Further time savings would come at a higher cost. Kummant says that to save an additional 10 minutes would cost $7 billion for new tunnels in New York and Baltimore, new bridges at other locations and track upgrades at five stations.

Truly high-speed rail requires a straighter, dedicated line built to highly exacting standards. David Gunn, who was fired as president of Amtrak in 2005 after a policy dispute, put it bluntly: “If you really want a super-zippy train from Washington to New York, you have to build another railroad.”