roadrailers, from the 'road side"
One of the problems that has plagued the road-railer and similar concepts is that of the extra weight of the various fittings for the rail use. Like trains road traffic must conform to certain limits on maximum gross weight of a vehicle as well as the axle loadings there on. This is general information for tractor trailers, semi trucks, eighteen wheelers, big trucks or what ever else you call a large truck towing a trailer operating on interstate highways in the United States.
First of all trucking is the business of moving freight. All freight has two important statistics when it comes to transportation, weight and volume. Any way you can get your equipment to increase its capacity in these areas is considered a good thing. There are ways to extend the capacity past the figures I am giving here but almost all of them differ from state to state. This information is for the classic truck tractor and semi-trailer combination using a "box" trailer (refrigerated or not). The maximum GCVW (Gross Combination Vehicle Weight) on most of the Interstate Highway System is eighty thousand pounds (80,000#); this is also the normal registered GCVWR (Gross Combination Vehicle Weight Rating) of most OTR (Over The Road) operators. Subtract the empty weight of the vehicles from this and you will get the carrying capacity of said vehicles. For most operations that would potentially use a road-railer this figure come to an industry "rule of thumb" of about 46,000# or about 44,000# for refrigerated operations.
Having talked to some drivers operating with road-railer equipment it is my understanding that a trailer so equipped is about 2,000# heavier than one without such equipment. This reduction in weight capacity is generally unacceptable to most of the industry. There are products that can benefit from road-railer service, however some of the fundamental differences in the two modes of transportation tend to negate the benefits.
Some definitions for those who may want them.
Truck Tractor -- a truck specifically designed for towing a trailer
Semi-trailer -- a trailer with one (or one group of) axle(s) which relies on another vehicle to distribute part of its weight. An example would be a boat trailer.
Full trailer -- a trailer with two (or two groups of) axles one of which usually pivots and does not require another vehicle to distribute its weight. An example would be a farm wagon.
Box Trailer -- a trailer with six fully enclosed sides, either insulated and refrigerated or not.
Gross Combination Vehicle Weight -- generally a regulatory term, it refers to total weight of two vehicles hooked together, for example a truck and trailer.
Weight Rating -- generally in conjunction with gross combination vehicle, a regulatory term referring to the maximum legally permitted weight for which the vehicle can operate (and has paid taxes for).
OTR or Over the Road -- This is an industry term that implies operations that do not end at the location they started at at the beginning of the work period, it further makes the implication that the truck has a sleeper berth for the driver to sleep in over night.
I hope I was able to clarify some things and did not obfuscate too much. The short version is road-railers did not catch on in wide spread use because they were not competitive enough in enough different markets.
