Tri-axle trailers are again in the news as another proposal for more legal gross weight is being floated in Congress. HDT Executive Editor David Cullen, has written about it for TruckingInfo, and I’m dissecting the mechanical end of it for HDT’s October issue.

In most places the predominant rig runs on five axles and can weigh as much as 80,000 pounds. This proposal would allow states to increase that to six axles and 91,000 pounds, which would boost productivity. Many states allow tractor-trailers and long combination vehicles that weigh way more than that.

Michigan “trains” and the LCVs in the Pacific Northwest are rather well-known examples. Less known, except to folks who live there, are heavy tractor-trailers in Maine, which operate with six axles at 100,000 pounds. These are also allowed in some nearby states and Canadian provinces.

And New York state has a permitting system that allows as much as 105,000 pounds on five axles. To people who run them, they’re no big deal because the heavy rigs are part of everyday work lives.

They do take precautions, such as using quality brake, hub and wheel components and making sure that only conscientious drivers operate them. Among other things, these guys take turns slowly and cautiously so they don’t tip over.

The Maine example is noteworthy because it partially refutes arguments against the six-axle, 91,000-pound proposal now in Congress.

The Truckload Carriers Association wrote a letter to the sponsoring congressman, Rep. Reid Ribble (R-Wis.), explaining why his proposal is not a good idea. The association said the cost of a higher-capacity trailer and tractor to operate at the higher weights would be $8,000 (just to add an axle) to $24,800 (for a stronger frame and kingpin, higher-rated tires and a more powerful engine in the tractor).

But is that really so? Todd Cotier, maintenance director at Hartt Transportation in Bangor, Maine, says some of his tractors are geared to pull the heavier trailers in hilly terrain, but “today everyone has more horsepower than they really need anyway, and our sleeper-cab road tractors can pull them without a problem.”

The strongest argument against heavier rigs is the lack of payback. Several times in the past, truckers have had to stretch trailers or buy new longer ones, but got little or no extra revenue from stingy shippers. Hard-nosed traffic managers demanded the bigger equipment and felt it was their right to stuff more cargo aboard, and that amount became the new “truckload.” Do it, or lose my business, shippers said.

So like many things in life, this issue will come down to economics. The “market” might be efficient (and it’s the basis for our free enterprise system), but it’s not always fair.