Dart Goes Lightweight

Dart Transit, a pioneer in high-cube trailers for hauling low-density freight, is now seeking lower tare weight to serve customers who ship heavier cargoes.

The result is a unique design that includes a double-sheet-and-post sidewall that's stronger yet lighter than those in plate-type trailers that constitute the great majority of its 7,800-unit fleet.

The Eco Trailer, as the company calls it, is part of Dart's Eco Fleet, a name chosen "to help promote the idea that we can haul more freight with fewer trucks," explains Dave Oren, Dart's president and the third generation involved in management of the family-owned company. There are also Eco Tractors with basic lightweight specifications and modified for optimum weight distribution.

"The trailer we pioneered has become so universal now, and we want to broaden our capabilities," Oren says of the currently common 53-foot-long by 102.3-inch-wide dry van. The Eco Trailer, also a 53-by-102, "can still handle the bulk but can also handle the weight. Customers tell us that they are more interested in putting more weight in the trailers, and they're pretty excited about this."

Beverages and paper products are the primary cargoes hauled in dedicated fashion by the Eco rigs. Nine of the newly configured tractor-trailers can handle shipments that would otherwise require 10 typical rigs, the company figures. This reduces operating costs, pollution and highway traffic.

Oren says he's not an engineer, but 30 years of experience in dealing with equipment helped him design and patent the sidewall. It uses a pair of aluminum sheets laid over vertical posts instead of a plate trailer's single metal sheet. Other features include wide-base single wheels and tires, and on-board tire inflation and weighing.

An Eco Trailer weighs 12,720 pounds versus 13,800 for a typical plate trailer with standard dual wheels and tires. "There's some mystery to this," Oren comments. "It should come out to be 700 or 800 pounds less according to manufacturer statements, but it scales at about 1,000 less."

Four "super singles," as Oren calls the wide-base tires and wheels, save 300 to 400 pounds over duals. The Michelin wide-base singles mount on steel wheels rather than aluminum because Oren wants to avoid theft. "We don't have a lot of experience with aluminum wheels," he says, but "my feeling is that they would be stolen" from trailers. He specs standard-width axles and offset wheels because wide-track axles are more expensive and not cost-effective.

Materials and products used in the Eco Trailers are common and readily available from various suppliers, and Oren selected those that would achieve the goals of light weight, efficient operation and low maintenance.

Dart began testing the design in 2004. Successful operation thus far led to it acquiring 100. An open-ended contract with the builder might result in another 300 or more, depending on experience. "Hyundai got the order because Hyundai would build them" with his sidewall design, he says.

In the sidewall, two 0.05-inch aluminum sheets are affixed to 0.4-inch-square vertical posts. The twin sheeting results in stiffness with light weight, and a sidewall is only 1 inch thick so the trailer's inside width is a high-cube-style 101 inches. The sheets' inside and outside surfaces are smooth to avoid pallet snagging and to reduce air drag at highway speeds. Battering of inside sheets usually does not spread to the outer sheets, so good appearance is maintained. And puncturing of an outside sheet leaves the inner sheet intact to keep out dirt and water.

Each sheet's length is 49 inches and its height averages 111 inches, with forward sheets of the wedge-shaped trailer being slightly lower and rear sheets taller. Bottom rails are 20 inches tall and double as interior liners. Other features of an Eco Trailer include:

* Composite laminated oak-and-fiberglass floor from Havco, which provides strength and protection against moisture damage to the wood and water intrusion to the trailer's interior.

* On-board weighing using an air-pressure gauge plumbed into the air suspension, to allow maximum legal loading. Depending on suspension and wheel-tire types, air pressure will indicate weight on the trailer's tandem. Oren says he has made up charts that convert pounds per square inch on a gauge to loaded pounds. The Eco Trailers use Hendrickson's Vantraax suspensions.

* Automatic inflation systems from Pressure Guard keep tires aired up for maximum casing and tread life and cargo loading.

* Andersen Eco-Flaps, with perforations that allow air flow to flow through for reduced drag and fuel consumption.

Prototype trailers from 2004 are performing well, Oren says, and if production models hold up, much of the entire fleet might eventually have the Eco design. Dart, based in Eagan, Minn., runs nationwide.

Eco Tractors

Dart Transit also has begun modifying its independent contractors' power units to Eco Tractor status, with the aim of light weight and maximum legal axle loadings. The goal is a top tare weight of 17,000 pounds including fuel and a driver for a tractor, typically a Freightliner Columbia with a 70-inch integral sleeper and a 12.8-liter Mercedes-Benz 4000 diesel.

Fixed fifth wheels are moved forward between 12 and 16 inches, based on a formula devised by Dave Oren, Dart's president. This transfers some weight to the front axle and increases available capacity of tandem drive axles. Another result of moving the fifth wheel is that the gap between tractor and trailer is shortened, which cuts air turbulence and reduces fuel consumption.

Wide-base tires and wheels are a consideration, but so far none have been retrofitted to the already lightweight tractors.

All of Dart Transit's tractors are owner-operated. The company says if you're a contractor interested in hauling heavier freight, the company has worked out a financing arrangement to help finance the needed modifications.

From the February 2010 issue of Heavy Duty Trucking.