Нужно подчеркнуть модальные глаголы и их заменители в тексте the elements of the track the track is often called the permanent way.it consists of rails,ties and ballast. the distance between the rails is called the gauge. the place where the ends of the rails meet in the track is known fs the rail joint. the rail joint has always been the weakest part of the track for neariy all the rails wear out at the ends. some railroads have two or more track. in order to make the trains pass from one track to another the railroads must have a switch which is a very important element of the track. the rails differ greatly in weight according to the kind of traffic which they are to carry when placed in the track.the largest and heaviest rails are laid in main line tracks because they have to carry the largest volume of traffic. the ties on most tracks were almost all of wood and in order to make them last longer they were treated with creosote. the ties are not laid upon the earth for the earth cannot support the track structure. they rest upon a bed of crushed rock or gravel,which is called ballast. ballast supports the track structure, holds the track in position and provides needed drainage.
