The shot in question on the train is not a single shot but there is a cut. At the beginning we see Commissaire Mattei at the window of a staticic train, perhaps a little camera movement,and then a quick camera pull back. It may even have been a set of a train side and train window shot on stage. It cuts to a helicopter shot of a real train with a compartment lit as the set is lit, and the camera onboard the helicopter pulls back and pans over the entire train and the countryside. I should add, it isn't a normal cut, but the 'A' side cuts to black, and then a quick fade-in is used to the 'b' side. Like an eye blink. There may have been some optical manipulation to match the windows and camera pull backs. It was effective certainly, but by adding the cut it made it manageable. Without a cut it would have been a very complex visual effect indeed composited on an optical printer or animation stand, probably more expensive and perhaps less effective. The process work of men driving in cars throughout the movie is not very convincing, but is on a par with most other movies of it's time. Henri Decae was a masterful DP, but even he couldn't make those process screen shots look real. Recently, I saw THE LOVERS, which he shot for Louis Malle, a gorgeous Black and White film, but the process shots of driving in autos weren't great. At the time we in the audience were used to accepting those shots in our filmic consciousness as "believable," though digital compositing has probably improved these types of shots with travelling matte work, tracking background programs, lighting programs to help perfect the look, even better color matching possibilites. Sometimes however it still looks phony. Remember all the bad process shots in Hitchcock movies, and somehow we mention those movies as embodying great technique. I agree though, the shot you mentioned was lovely and important.
pardon us our troubled quietnesses.