“ In one a train is the unit and in the other a car. As the context shows, a train in the sense intended consists of an engine and cars which have been assembled and coupled together for a run or trip along the road. When a train is thus made up and is proceeding on its journey it is within the operation of the air-brake provision. But it is otherwise with the various movements in railroad yards whereby cars are assembled and coupled into outgoing trains, and whereby incoming trains which have completed their run are broken up. ”

“ We cannot assent to the view that the yards at Jersey City, Weehawken, and Bergen are but a single yard. They doubtless are important accessories to the defendant's estern terminal, but that does not make them one yard. They lie from 2 to 3 1/2 miles apart, are not so linked together that cars may be moved from one to another with the freedom which is usual and essential in intrayard movements, and are in actual practice treated as separate yards. ”

“ Their speed is from 7 to 18 miles an hour and they move great numbers of cars in each direction every day. All go through the tunnel, which is admitted to be very dark, and upon each trip they pass over several switches leading to other tracks, traverse part of the same line over which fifteen regular through and local freight trains are moved each day, and cross at grade tracks which are in daily use by approximately thirty-five passenger trains. ”