I haven't noticed this covered elsewhere yet, but if it has been, please direct me accordingly. I am interested in the procedure when splitting/joining trains formed of class 377s. I travel via Redhill, where many workings undergo this process and it is very unusual for it to take less than about five minutes, especially when joining, and even when the train is running late. My query stems from last evening, when the 1659 London Bridge to Horsham/Tonbridge, which joins at London Bridge and usually takes the customary five or more minutes to do so, was joined in around two minutes. The first portion was in the platform (with some passengers already aboard) and the second portion arrived, disgorged its passengers in about 30 seconds and some passengers then boarded before the doors closed and locked. We coupled up, and the doors were released again after only another minute or so, making it by far the quickest I have known this to happen. The question is, if it can be done this fast, why is it almost always not, even when running late?