We've all been there, waiting on a train at a railroad crossing, or stuck in a traffic jam that doesn't appear to be going anywhere for awhile. Well transmissions are designed to my understanding for you to go, much more so then to stay the brakes at a stop. So during times of prolonged stopping, should you put your car in park to prevent transmission from overheating or is this really not necessary in modern cars?
The transmission will get hotter if it is working at maximum, such as towing a trailer uphill, that will be when the transmission cooling system will be needing to work at maximum and, if the cooling air flow is dirty or obstructed, when the problems will occur.
But using park or neutral will take the load off the drive train in the box and reduce the fuel consumption a small amount.