The shift from rail to truck started before World War 2 on a nationwide basis. In Southwestern Colorado, it kicked into high gear after the war. It was not just in the Alamosa to Durango market, but remember that the NG was being abandoned in huge pieces after 1950. The reasons for this are many, but first was that before WW2, virtually all of the highways in SW Colorado were gravel, not paved and keeping them open in winter was most difficult. In the early 1960's both Colo - NM hwy 17 over Cumbres and Colo 145 between Rico and Telluride were not paved, at least not all the way. I remember the old Colorado highway maps of the time with these highways labelled "closed in winter". A gravel highway simply cannot support the sort of truck traffic that would be required to replace a train of any length. At the same time, the semi trailers of the time were not anything like the 18 wheelers that we have today going down the road hauling pipe, etc. Most of the tractors were only 6 wheel affairs and trailers only 4 wheels, not 8, so the amount of load that could be hauled was much less. As the highways were paved and improved, the size of the trucks grew, and the load capacity with them. Also with better roads, the trucking companies could provide more punctual and timely service as opposed to rail and for many shippers the increase in cost to ship by truck was negated by the ability to receive shipments on time, and not have to warehouse supplies and store them because you had to order well in advance of use to be sure of having an item in stock if you depended on rail delivery.
I have been told that the Rio Grande had actually done studies that showed the virtually all of the NG west of Alamosa could have been replaced by the Motorway, and were preparing to go to the ICC with those studies and ask for abandonment of the NG, when El Paso Natural Gas notified them of the start of the pipe shipments. They quickly put pencil to the paper and after calculating the costs involved in purchasing the number of trucks and trailers required as well as hiring the drivers, etc, that the shipments were still more economical to handle by the NG than by trucks simply because of the sheer volume involved. The investment to cut down and strengthen the old gondolas, and to convert old SG flats to NG was substantially less than the cost of new trucks and the labor costs to run the trains and convert the cars was also much less than the hiring of truckers.
