The video is a promotional video for Alco and GE featuring a new FA1-FB1 locomotive set used by the New York, New Haven and Hartford Railroad in Southern New England on its route between Maybrook, NY and Cedar Hill (New Haven) to replace the steam locomotives that worked the line. With the steep grades on the line, the NH used helpers at various points to move the freight across the route.
Today, the New Haven Railroad still exists as a crucial link of the Northeast Corridor between New York City and Boston. The remaining portions of the mainline to Maybrook and other existing branches serve some freight but mostly commuters between New York City and Connecticut suburbs.
The Maybrook to Danbury portion is no longer a through route thanks to the Penn Central Railroad. One of the dumbest requirements from the ICC for the Pennsylvania-New York Central merger was to include the small New Haven. This led to a quicker demise of the New Haven than Patrick Mc Guiness had started with his pilfering. Cedar Hill Yard still exists but it's a pretty dismal sight today with only a few tracks in use compared to the miles up miles of classification yard shown in the video.
According to various sources, PC management hated the New Haven and did whatever they could to ruin it. In the early 1970s, the Poughkeepsie Bridge across the Hudson River burned due to a suspicious fire, thus cutting the mainline and western connection of the New Haven Railroad. Many people believe that this was to force freight across Penn Central's own lines through its gateways in the greater New York City metro region instead of north of the city across the New Haven and on to the B&M and other points north.