Ever wonder what the difference between A Trains and B Trains were? Did you even know about the existence of C Trains? This article explains the different ways that two trailers are hooked to one another in North America. When you refer to a set of trailers as A, B or C trains you are really referring to the type of connection between the two.
A Train Semi Truck Trailers
This type of semi truck is connected by a dolly that is hooked up to a pintle hook on the rear of the forward trailer. The dolly has one or two axles, and it is licensed as a separate trailer.
Single axle A Trains are used extensively by the LTL industry. Companies like Estes, UPS, and Con-way use them to run between terminals, and will break up the trains for final delivery. Double axle A trains are used as well, but more often for Long Combination Vehicles, to put two 48’ or 53’ trailers together. A Trains are mostly used for pulling Van (enclosed) trailers.
B-Train Semi Truck Trailers
B-Trains are a truck-trailer combination where the axles of the lead trailer stick out and a fifth wheel is mounted on the lead trailer.
These combinations are used sometimes by LTL carriers, where the axles of the lead trailer slide from underneath the lead trailer so it can back into a door just like a regular trailer. Food service companies like Sysco systems also this type of trailer as well to extend their distribution network. A set of two can be pulled, usually overnight, to a city within 500 miles of the distribution center. Then, the trailers broken up and are taken by two fresh drivers for deliveries to restaurants and their other customers.
The B –Train combination is also very popular for hauling flatbed, bulk and liquid goods in Canada and some US states. Because these types of operations usually don’t require backing up into a dock, drivers will generally only drive forward, making it easier. However, most drivers that pull these on a regular basis can back them up fairly well, even into a dock or around a corner. The 8 axle, 63,500 kg B Train is a standard across Canada.
C-Train Semi Truck Trailers
C-Trains are the rarest of the double trailer combinations. Like an A-Train, the lead trailer pulls a dolly that the second trailer sits on. However, instead of one pintle hook, there are two. This removes one of the points of articulation from the unit, and makes the second trailer much more stable. However, it also makes it a lot harder to hook the dolly to the lead trailer, and the tires on the dolly will wear much quicker from going around corners.
I am only aware of C-Trains operating in Western Canada, pulling long combination vehicles, not shorter double trailers.
D- trains are also a thing. But i don’t think they have ever been used and mostly exsist on paper!
How do C-trains steer? Seems like the dual pull bars would make for an extremely rigid wheelbase by comparison.
I work with trains that the dolly is a part of the rear trailer and is attached on a bearing plate, it is unattachable. What would that be considered?
Yes, it is intended to make the dolly rigid with the lead trailer. The dolly will skid around the back of the trailer and it will have the effect of extended the ‘real’ wheelbase of the lead trailer.
Even if the dolly is permanently attached, it is still considered an ‘A-train’.
some C-Trains have steer axles on the front
What I can’t seem to find is who coined or came up with designating these coupling types as A, B & C? I’m guessing sometime in the 60’s or 70’s and possibly somewhere in Canada?
Hello, I think that the A train is called an A train because the connecting dolly looks like an ‘A’. The ‘C’ train dolly also looks like its namesake. I’m not sure where the ‘B’ train name came from!
From what I’ve heard C trains were just garbage, reason they’re so rare today. Like it said wore out tires like crazy and if I’m not incorrect I’m pretty sure when they’d turn the two connection points would put strain on the frame and the two points would break a lot.
C trains predominantly use steering axles.. They give the stability of a B train but with a removable converter.. The A , B ,C designation I believe is from the order of invention.. A converter with a turntable rather than a 5th wheel is classed as a Full Trailer. It isn’t a converter if it can’t unhook.
Thanks for the comment!
Gordon Foods uses single axle C dollies extensively with 28′, 30′, and 36′ trailers throughout western Canada. They use them for trailer transfers from their main hub to rural Depots throughout the rest of the province.
The dolly axle does steer, it’s connected to the 5th wheel. However the axle has an air actuated steering lock which can be engaged to lock the wheels straight making it easier to back the B box into a dock, disconnect the A box, park the dolly, then put the A box into the door next to the B box. They do it this way because the length of trailer needed for the load varies daily, as does where the trailers go. It could be used locally to the distribution centre one day, then reloaded and sent to a rural depot overnight. Using the C dolly is a compromise between the stability and backing up ease of a B train, without the cost of buying hundreds of slide-axle B train trailers.
And yes, they are hell to connect. You have to back up to it perfectly in order for it to drop right into your pintle mounts. But like anything, once you get good at it, it becomes second nature.
The ‘C’ train dolly on the illustration shows a 2-axle configuration. I have never seen such a one in real life. I pulled a single-axle version for a time, and that axle was on a turntable and would swivel to follow without scrubbing. The short ‘pup’ trailer on the dolly would actually follow within the radius of the lead trailer, allowing pretty narrow turns. That turntable could be locked in place to facilitate backing, although I never had to.
I pull C trains in BC and I love them! Typically either two 28′ or 30′ pup trailers (6-axle), or a 36′ lead and 28′ pup (7-axle). Our C dollies have a steer axle, but with an air actuated lock, so the dolly can be locked straight for backing up.
They can be a bit of a pain to connect sometimes, but with some practice and skill at precise backing, you can get the pintles to line up in 1-shot almost everytime.
I run some of the mountain passes of BC, so the added stability of the C dolly vs. an A dolly is a necessity in the winter when the road becomes a skating rink. And being able to lock the dolly to essentially make the combination behave like a B train when backing up is extremely useful!
Hello
A,B,C has nothing to do with the order of invention.
A – Train Semi Truck Trailers
A train is connected by a dolly that is hooked up to a pintle hook on the rear of the forward trailer. The dolly has one or two axles, and it is licensed as a separate trailer.
Single axle A Trains are utilized to keep running between terminals
Double axle A trains are used for Long Combination Vehicles, to put two 48′ or 53′ trailers together. A-Trains are used for pulling Van (enclosed) trailers.
B-Train Semi Truck Trailers
B-Trains are a truck-trailer combination where the axles of the lead trailer stick out and a fifth wheel is mounted on the lead trailer. The axles of the lead trailer slide underneath the lead trailer so it can back into a door/opening just like a regular trailer.
The operation of these trucks usually don’t require going back to a dock, drivers simply drive forward, making it less trying. The drivers that do drive these trucks, however, have a tendency to be experienced and can back into docks or around corners in spite of the size of their trucks.
C-Train Semi Truck Trailers
The lead trailer pulls a dolly that the second trailer sits on. There are two pintle hooks, which remove one of the points of articulation from the unit. This makes the second trailer significantly steadier.
That is really cool that the C train can have steer axles which can be locked straight, thanks for the feedback!
Thanks for your comment!