Many states now allow triple-trailor rigs…and I can tell you, they are SCAREY! Being passed by one is like being passed by an ocean liner. However, I could well imagine that strings of trailors (like freight trains) could save a lot of energy. Think aboiut it…you have a monster tractor in front (say 6000 HP) with a 100 gear transmission. You hook it up to 10-15 trailers, and put a caboose on the end…then you can ship 16 loads of lettuce from Phoenix to NYC, for the cost of one trailer load. Would this work? As long as the drive paid attention (and car drivers too!) I can see such a scheme being possible.
Is this leagal?
Ah, we have them already. They’re called trains.
BTW, …
Source: http://www.guinnessworldrecords.com/content_pages/record.asp?recordid=43494&Reg=1
Seriously, can you imagine the traffic snarls, at intersections, on/off ramps, pulling into/out of a deisel station? With enough idiot drivers on the road already, would you want to be the driver of a road train?
Road trains in Australian usage are generally confined to the kind of highway where there is NO traffic to jam.
Exactly. Junctions, depots etc. would all need to be built specifically to cater for half-mile-long units. By which stage, you might as well build a railway. (Or make better use of one that already exists.) The major advantage of road haulage is being able to take small units to individual destinations, at specific times. The larger the vehicle, the less this advantage applies. Except for very few cases (fuel for power plants, for example), you’d end up with a depot where the road train was split up into individual units for local distribution - once again, exactly how railways work.
One sometimes sees trains made up in whole or in part of flatcars carrying two semi-trailers each. Trailers are loaded at the shipment point, brought by normal “tractor” rigs to sites where they can be loaded onto flatcars, which are pulled by a diesel locomotive to the destination community, then unloaded and attached to other rigs to be taken to the actual destination points. It’s an element of multimodal shipping. Another is to have boxes resembling a short semi-trailer but without the undercarriage, which are placed on cargo ships for ocean transport, then loaded onto railway flatcars and/or flatbed trailers to be hauled to the destination.
They must be widely used in mid-continent Australia. Saw one in Aussie movie where camera was close to the path and it was very impressive.
The size of the tractor, number of trailers, etc. would be dictated by economics of distribution of goods to where and how often.
In US, UK, or EU they would be limited by available roadways, and other factors including legal restirctions.
Not to mention fast food drive-thrus.
If you didn’t have a supersized engine to pull the road train, performance would be just terrible, terrible.
Besides, the much vaunted advantage of trucks over trains is that they are flexible and can handle local deliveries, and can be rerouted. A road train, because of the special roads and facilities needed, would lose most of that flexibility, at which point shippers would say we might as well ship by regular train with pickup by local truck.
Actually I never saw a large motor vehicle that performed as well as a car in terms of acceleration. If public transit buses could at least keep up with the cars on the street between stops, they’d attract more riders.
If you have to pay the capital, maintenance and fuel costs for a 6000-hp tractor, I think it’s fair to say that costs would be greater than for a single tractor-trailer load (though perhaps less per ton of freight).
And about that caboose - why do you want it? Note that these are largely gone from freight trains.
I wouldn’t bother with the transmission. A truck like that would probably be better off with diesel-electric, like a locomotive.
And given the limited routing options, maybe a guiding system using wheels with a guiding edge, and roads lined with steel ‘rails’…steel-on-steel would also make for a very efficient system for acceleration (contrary to popular perception)…
Hmmm… interesting. And you might raise the steel lining of the guidepaths, instead of embedding it – less chance of corrosion, and easier to maintain – except, of course, where it crosses a non-guided highway. The corporations that own the big hauling engines could agree to put in the infrastructure, letting other companies use it for a fee – unless you nationalized the operation, since it’s obvious that with few routing operations, it’ll be a oligopolitan system with only a few large companies able to build and run the equipment.
We may have hit on a great new concept here!! 
I think the way this idea is working out in actuality is a “beam guided” system I believe. Trucks get onto the highway and are switched onto computer control. Computer can line them all up couple feet apart. This is the cheapest route: use existing infrastructure with a few add-ons.
Saw a show about it the other week. Here’s a Radio Netherlands site discussing it:
A Virtual Train of Trucks
They are still a pain in the arse though. They operate on long single lane (ie one each way) roads in the middle of Australia where the visibility due to heat haze can be very poor. If you want to pass one you need to pull out into on-coming traffic, and often you just can’t see far enough ahead to tell if there are any cars coming, even if the road is dead straight for 100 miles.
It’s even less fun being in a car going the other way. Cruising along at 160kph (no speed limit in the Northern Territory of Aus) and coming across a road train getting over taken by some dude who really has no idea of just how long they are and can’t see you until he has no escape route.
Has the number of road trains in Australia decreased with the opening of the railway to Darwin?
I’m not sure. I didn’t drive on the highway enough to notice any difference between now and the before-time.
Is there a legal or practical limit to the number of trailers in Aussie trains? What is the usual number in common use?
In answer to the OP’s question “Are ‘road trains’ feasible?” the answer, according to the AAA road safety study here is a definite maybe. They may work, but there is still controversy over whether they are safe as compared to smaller units. For my part, I would just agree with ralph124c that they are scarey, and then ban them everywhare on that basis. But, it’s a lot more complicated than it seems. It is certain that even in states where they are allowed, longer combination units are restricted to certain highways, or portions of highways. I would just avoid those portions.
The usual number is three or four trailers. Most cattle trucks are three and you see quite a few four trailer fuel trucks (bottom right photos). Anything more than four is extremely rare, and the trailers will likely be smaller than usual.
Here is another example.
here and here are some early style road trains before the australians perfected the concept.
As you can see from this picture, it is necessary to tell australians that they are in fact looking at a road train and not a caravan, or bicycle for example.
The practicalities are limited by how far in to town you can go. A road train can really only get to the out lying industrial area before its trailers need to be seperated. Some towns have signage to show where a road train can and can’t go.
I remember about ten years ago there was a pseudo-PSA commercial about not allowing nationwide triple tractor trailors. I say pseudo because if you looked at the fine print at the end of the ad you saw that it was actual sponsered by the Railroad industry. The ad featured a woman driving a minivan with a kid in a car seat being passed by the big, bad truck. Really annoyed me (like the RR industry really gives a crap about highway safety).
As far as problems driving them thru intersections or drive-thrus, um, you guys do realize that multiple trailors are only allowed on interstates, right?
I think triple trailors should be allowed on interstates nation-wide. Big rigs are operated by professional drivers. A bigger danger would be from the dumb broad in the minivan wetting her pants because a big scary truck passed her!