Most likely it is exhaust steam from the turbogenerator which produces electricity for locomotive appliances. The whine of these important devices, which usually sit atop the boiler near the cab, was a background sound when one was in an engine terminal or busy station. It was quickly overridden by exhaust blasts, the sounds of stretching draft gear, straining metal and complaining roadbed once the engine was in motion. This nine-car train, rolling along the elevated roadbed, appears to be a profitable run but we can't tell for sure without a glimpse of the conductor's passenger count, the waybills for the two milk cars or the volume of express in the headend cars. When the hotelmen heard transportation complaints from their customers they were forwarded to the railroad's office in Middletown with suggestions for improvement.
Good fences make good neighbors.
Even with the most diligent effort on behalf of both property owners, farm animals managed to find an occasional break in the wire or a careless trespasser left a gate open and a wayward cow, sheep or horse wandered onto the tracks to meet its end with the passage of the next train. The owner sometimes inflated the value of the animal killed and railroad claim agents were well aware of the practice. Another claim might be made when sparks or cinders from a passing train set fire to a field of valuable grain or even a crop of hay. The state would also prosecute if state forest lands took fire from the same cause.