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[quote user="TomDiehl"]  So intermodal with different names isn't related. Trailer Train 86 foot TOFC flatcars aren't related to Thrall Industries 5 unit articulated cars. One is an earlier experiment with hauling truck trailers on the rails, the latter a refinement of the concept. All steps between the two weren't a success. The Front Runner cars come to mind. [/quote] It is interesting that you bring up the Front Runners.  Basically taking outdated TOFC cars (too short to host two 48+' trailers, too long to carry just one without wasting space) and combining them via drawbar to allow three long trailers to ride on the two platforms with no wasted space.  A good way to utilize otherwise obsolete equipment.  But in no way an innovative forward thinking plunge into technological superiority.  The Front Runners were still overly heavy on the tare compared to spine cars and the TTOX/Four Runners.  What was saved in using available equipment was lost in the extra fuel costs.  The TTOX/Four Runners were much better potential adaptation of using existing equipment and modifying it to conform to the evolution of the highway trailer, but alas such was an opportunity lost due to undocumented speculation regarding the single axle bogies and the subsequent spacing on the units themselves. According to my source at Gunderson, the TTOX/Front Runners were perfectly good TOFC cars, no more prone to problems than any other intermodal flat car, yet they saved 5000 lbs per platform over regular spine cars, or about 300 tons per train.  300 tons may not seem like much to an industry that regularly hosts 16,000 ton unit trains of coal, but for the high hp/t ratios of TOFC's such a weight savings adds up. The TTOX ran up against increased trailer lengths from 48' to 53', but when in the Four Runner "four pack" configuration, all it would have taken to permit the longer trailers would have been an adjustment to the drawbar length to permit overhang of the trailers (most 53's have the same kingpin to rear wheel length as a 48' trailer, excepting the heavy haul 53's which would have required extending the wheelset platforms).  Running the drawbar all the way into each unit's center sill above the single axle would have improved the curving characteristics of the lengthened units, while still maintaining the lighter tare weight advantage of the concept.  Instead, the railroads junked the concept completely. Now, before you say "perhaps it wasn't worth the effort to modify the cars, easier to just buy newer spine cars", keep in mind TTX has had an ongoing program of equipment modification.  They recently commenced a program of lengthening the standard 48' per platform 5-pack spine cars into 53' per platfrom configuration, which requires adding a major amount of material to the "spine" itself.  Alot more complicated than just extending the drawbar configuration of the Four Runners. The other option would have been to adjust the length of the spine on the Four Runners themselves, and add a standard two axle articulation between the "A" and "C" units and the "D" and "B" units, keeping the drawbar between the "C" and "D" units.  This would have produced a hybrid of single axle bogies on one end of each platfrom and articulated two axle bogies on the other end of said platform.  This would have added some tare to the consist, but such would still have been lighter than the standard 53' articulated spine cars, and should have aleviated any concerns about the curving characteristics of the units.
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