An analysis of the air in Altoona, Pennsylvania in the 1970’s would have revealed that the four most predominate components of that air were nitrogen, oxygen, diesel exhaust, and brake shoe smoke. Here a loaded coal train arrives at the bottom of the grade over the Alleghenies amid a cloud of that fourth component. It doesn’t seem like two GP35’s are enough to get this train over the road, but wuth the aid of two more pushing on the caboose, they did the job.
