While rail freight transportation in New York City and Long Island has atrophied (most freight activity takes place in northern New Jersey), the city has more frequent passenger rail service (intercity and commuter) than anywhere else in the nation. Intercity service is provided by Amtrak. Fifty-four trains run each day on the busiest route—the Northeast Corridor from New York to Philadelphia. For trips of less than to other Northeastern cities, Amtrak is often cheaper and faster than air travel. Amtrak accounts for 47% of all non-automobile intercity trips between New York and Washington, D.C. and about 14% of all intercity trips (including those by automobile) between those cities. Amtrak's high-speed Acela trains run from New York to Boston and Washington, D.C., via the Northeast Corridor, using tilting technology and fast electric locomotives. New York City's Penn Station is the busiest Amtrak station in the United States by annual boardings. In 2004 it saw 4.4 million passenger boardings, more than double the next busiest station, Union Station in Washington, D.C.