The shared tracks of the Long Island Rail Road (LIRR) Main Line and Amtrak's Northeast Corridor pass along the southern edge of the yard.
Northeast of the yard a balloon track (or reverse loop) is used for "U-turning" Amtrak and NJ Transit trains which terminate at Penn Station.
[1]: 93 At that time, Sunnyside was the largest coach yard in the world, occupying 192 acres (0.78 km2) and containing 25.7 miles (41.4 km) of track.
In May 2011, a $294.7 million federal grant was awarded to address congestion at Harold Interlocking, the United States' busiest rail junction, which is part of the yard.
The work will allow for dedicated tracks to the Hell Gate Line right of way for Amtrak trains arriving from or bound for New England, thus avoiding NJT and LIRR traffic.