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<p>[QUOTE=&quot;beastr123, post: 12179924, member: 133408&quot;]I grew up with my dad working as a mechanic for what was a medium sized bulk transport company that began buying others to expand their market. This was in the mid 60s. Maccam Transport (laterTrimac) did not pioneer &quot;doubles&quot; or A-trains but were very early adopters.</p><p>Doubles were equal length trailers connected by a single axle converter that has a 5th wheel plate on top and the trailers&nbsp; were also single axle and normally 24 to 28 ft long so that with a short cab-over tractor they could maximize capacity within the restrictive length laws. This was 60 ft and up to 65 ft in most jurisdictions at that time.</p><p>Doubles originally had to stay in the same max weight rules as a 5 axle semi trailer.</p><p>When we were allowed more weight for extra axles in the late 60s then short tandem trailers with single axle converters were allowed all though a restricted max weight (in Western Canada 110,000lbs).</p><p>Bulk A-trains came from that rise in gross weight increase. The 110,000 weight was on major(primary) roads only and smaller roads and lighter built(secondary) roads were a lot more restricted.</p><p>In western Canada at that time secondary roads were restricted to 74,000 lbs.</p><p>Bulk carriers started building shorter tandem axle trailers with larger capacity and a pintle hitch on the back,then an even shorter single axle trailers with a turntable axle/hitch on the front. When pulled by a short cab over tractor they could still stay under the length laws and carry up to 40% more load. The other advantage was that some areas could take a partial load on the primary road then a &quot;full&quot; secondary load further on.</p><p>B trains were found to be even better for some things due to better stability and ease of backing but were not as versatile for split loads.</p><p>&nbsp;As the weight and length laws changed in the 70s then super B trailers became feasible.</p><p>C-trains were used some and were found to be almost as stable as b-trains but again had maneuvering restrictions for the average driver. They are still used somewhat in the ltl industry but seldom in bulk carriers.[/QUOTE]</p><p><br /></p>

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