The first B&O train to arrive with passengers was the Pittsburgh Express, which did so at 6:50 a.m. on October 27, 1907, while the first PRR train arrived three weeks later on November 17.
The main building itself was completed in 1908.
Of its 32 station tracks, 20 enter from the northeast and terminate at the station's headhouse.
The remaining 12 tracks enter below ground level from the south via a 4,033-foot twin-tube tunnel passing under Capitol Hill and an 898-foot long subway under Massachusetts Avenue which allow through traffic direct access to the rail networks both north and south of the city.

Among the new station's unique features was an opulent "Presidential Suite" (aka "State Reception Suite") where the U.S. President, State Department, and Congressional leaders could receive distinguished visitors arriving in Washington.
Provided with a separate entrance, the suite (which was first used by 27th  President William Howard Taft in 1909) was also meant to safeguard the Chief Executive during his travels in an effort to prevent a repeat of the July 1881 assassination of 20th President James A. Garfield in the old former Baltimore and Potomac Railroad Station.
The suite was converted in December 1941, during World War II to a U.S.O. (United Services Organization) canteen, which went on to serve 6.5 million military service members during World War II.
Although closed on May 31, 1946, it was reopened in 1951 as a U.S.O. lounge and dedicated by President Harry Truman as a permanent "home away from home" for traveling U.S. Armed Services members.

On the morning of January 15, 1953, the Pennsylvania Railroad's Federal, the overnight train from Boston, crashed into the station.
 When the engineer tried to apply the trainline brakes two miles out of the platforms, he discovered that he only had engine brakes.
A switchman on the approach to the station noticed the runaway train and telephoned a warning to the station, as the train coasted downhill into track 16.
The GG1 locomotive, No.
4876, hit the bumper block at about 35 miles per hour (56 km/h), jumped onto the platform, destroyed the stationmaster's office at the end of the track, took out a newsstand, and was on its way to crashing through the wall into the Great Hall.
Just then, the floor of the terminal, having never been designed to carry the weight of a locomotive, gave way, dropping the engine into the basement.
The 447,000-pound (202,800 kg) electric locomotive fell into about the center of what is now the food court.
Remarkably, no one was killed, and passengers in the rear cars thought that they had only had a rough stop.
An investigation revealed that an anglecock on the brakeline had been closed, probably by an icicle knocked from an overhead bridge.
The accident inspired the finale of the 1976 film Silver Streak.
The durable design of the GG1 made its damage repairable, and it was soon back in service after being hauled away in pieces to the PRR's main shops in Altoona, Pennsylvania.
Before the latter action was undertaken, however, the GG1 and the hole it made were temporarily planked over and hidden from view due to the imminent inauguration of General Dwight D. Eisenhower as the thirty-fourth President of the United States.

Until intercity passenger rail service was taken over by Amtrak in 1971, Union Station served as a hub for the Baltimore and Ohio Railroad, Chesapeake and Ohio Railway, Pennsylvania Railroad, and Southern Railway.
The Richmond, Fredericksburg & Potomac Railroad provided a link to Richmond, Virginia, about 100 miles (161 km) to the south, where major north–south lines of the Atlantic Coast Line Railroad and Seaboard Air Line Railroad provided service to the Carolinas, Georgia, and Florida.
 World War II was the busiest period in the station's history in terms of passenger traffic with up to 200,000 people passing through on a single day.
The first B&O train to arrive with passengers was the Pittsburgh Express, which did so at 6:50 a.m. on October 27, 1907, while the first PRR train arrived three weeks later on November 17. The main building itself was completed in 1908. Of its 32 station tracks, 20 enter from the northeast and terminate at the station's headhouse. The remaining 12 tracks enter below ground level from the south via a 4,033-foot twin-tube tunnel passing under Capitol Hill and an 898-foot long subway under Massachusetts Avenue which allow through traffic direct access to the rail networks both north and south of the city.
Among the new station's unique features was an opulent "Presidential Suite" (aka "State Reception Suite") where the U.S. President, State Department, and Congressional leaders could receive distinguished visitors arriving in Washington. Provided with a separate entrance, the suite (which was first used by 27th  President William Howard Taft in 1909) was also meant to safeguard the Chief Executive during his travels in an effort to prevent a repeat of the July 1881 assassination of 20th President James A. Garfield in the old former Baltimore and Potomac Railroad Station. The suite was converted in December 1941, during World War II to a U.S.O. (United Services Organization) canteen, which went on to serve 6.5 million military service members during World War II. Although closed on May 31, 1946, it was reopened in 1951 as a U.S.O. lounge and dedicated by President Harry Truman as a permanent "home away from home" for traveling U.S. Armed Services members.
On the morning of January 15, 1953, the Pennsylvania Railroad's Federal, the overnight train from Boston, crashed into the station.  When the engineer tried to apply the trainline brakes two miles out of the platforms, he discovered that he only had engine brakes. A switchman on the approach to the station noticed the runaway train and telephoned a warning to the station, as the train coasted downhill into track 16. The GG1 locomotive, No. 4876, hit the bumper block at about 35 miles per hour (56 km/h), jumped onto the platform, destroyed the stationmaster's office at the end of the track, took out a newsstand, and was on its way to crashing through the wall into the Great Hall. Just then, the floor of the terminal, having never been designed to carry the weight of a locomotive, gave way, dropping the engine into the basement. The 447,000-pound (202,800 kg) electric locomotive fell into about the center of what is now the food court. Remarkably, no one was killed, and passengers in the rear cars thought that they had only had a rough stop. An investigation revealed that an anglecock on the brakeline had been closed, probably by an icicle knocked from an overhead bridge. The accident inspired the finale of the 1976 film Silver Streak. The durable design of the GG1 made its damage repairable, and it was soon back in service after being hauled away in pieces to the PRR's main shops in Altoona, Pennsylvania. Before the latter action was undertaken, however, the GG1 and the hole it made were temporarily planked over and hidden from view due to the imminent inauguration of General Dwight D. Eisenhower as the thirty-fourth President of the United States.
Until intercity passenger rail service was taken over by Amtrak in 1971, Union Station served as a hub for the Baltimore and Ohio Railroad, Chesapeake and Ohio Railway, Pennsylvania Railroad, and Southern Railway. The Richmond, Fredericksburg & Potomac Railroad provided a link to Richmond, Virginia, about 100 miles (161 km) to the south, where major north–south lines of the Atlantic Coast Line Railroad and Seaboard Air Line Railroad provided service to the Carolinas, Georgia, and Florida.  World War II was the busiest period in the station's history in terms of passenger traffic with up to 200,000 people passing through on a single day.
Washington Union Station