Stepping into Twin 33 Trailers

According to Knipling, advanced safety features such as automatic braking or electronic stability control have made the US road network safer than ever before, with commercial vehicles now widely considered less accident-prone than the average passenger vehicle. “The accident rate for trucks is now one-third the rate for passenger vehicles,” he explains. “In fact, recent innovations such as lane departure warning and forward collision warning systems [now] collectively reduce thousands of crashes a year.”

To build on that hidden success story and continue to increase road safety in his home country, Knipling says the local transport industry will have to continue reducing the number of vehicles on the road, as well as overall miles driven per unit. One way to do so, he shares, is increasing the efficiency of next-generation trailing equipment – a strategy successfully put into practice in Australia, Canada, South Africa and Scandinavia, where High Productivity Freight Vehicle (HPFV) design has seen a veritable boom over the past half decade. “Large truck traffic carries inherent risks, even when trucks are driven safely,” he explains. “A way to reduce that risk is to deploy fewer, higher-capacity vehicles. This would mean relatively fewer truck miles driven and less exposure to risk.”

To find out just how the HPFV trend could help reduce commercial vehicle traffic in the US, a transport lobby group asked the ex-Virginia Tech Fellow to examine how increasing the maximum length of so-called twin trailers from 28 feet (ca. 8.5m) to 33 feet (ca. 10m) would impact the local freight market.

Knipling’s 19-page analysis of the issue, aptly titled Twin 33 Foot Truck Trailers: Making US Freight Transport Safer And More Efficient, was made available for download in March and continues to stir up the North American Less-Than-Truckload (LTL) market, where the double trailer set-up is most prevalent.

According to Knipling, it is inspired by a 2015 study by the US Department of Transportation’s (DOT) Federal Highway Administration that analysed and modelled six possible changes to both trailer size and number – one of which was the use of twin 33-foot trailers without increasing the current gross combination weight of 80,000lbs (ca. 36 tonnes). The prospective policy change was referred to by the DOT as the T-33 shift.

“The DOT [already] modelled numerous economic and societal benefits resulting from a T-33 shift,” he says. “Operational cost savings would be more than six per cent within the LTL transport niche, amounting to more than US$2.5 billion (€2.36 billion) in 2014 and increasing annually. Based on DOT estimates, current truck vehicle miles travelled would be reduced by more than three billion, with associated reductions of more than 4,500 annual truck crashes.”

He argues, “Although twin trailer trucks are a small percentage of the overall traffic stream, permitting T-33s would reduce annual US traffic delays by more than 50 million hours, with congestion-relief savings of nearly $1 billion (€945 million).”
From an industry perspective, Knipling says a key concern is that the current length and weight limits for twin trailers date back to 1982 and were set in accordance with the technology of the time. “The 1982 restrictions were based on the safety designs and operational uses of twin trailers 35 years ago,” he stresses, adding practice has since shown that twin 28-foot trailer configurations “cube out” well before they reach the maximum weight limit – mainly because they usually carry dry consumer goods such as food, paper goods, toys or electronics. An additional 1.5m of cargo space would help fill the payload gap and cushion the impact converging megatrends such as urbanisation and e-commerce will have on transport.

“The American marketplace and transportation system have changed dramatically since 1982, and the pace of change is accelerating,” he explains. “Most notable has been the growth of e-commerce. E-commerce has become a staple of American life, as e-commerce sales have doubled in seven years and in less than five years will account for 10 per cent of all retail sales. This continuing shift in commerce requires corresponding shifts in transport strategy and equipment.”

According to Knipling, traditional retail is supplied largely by truckload shipments of product delivered directly to central outlets. In contrast, e-commerce would generate many smaller shipments destined directly for end-consumers located across the country, thus demanding a different delivery strategy.

“Cost-efficiency and timeliness of delivery favour a system of scheduled, synchronised truck trips throughout a network where each truck carries whatever variety of products has been purchased,” he says. “The LTL freight transport sector makes this market model possible – products are shipped to distribution hubs where they are sorted and delivered to consumers. Twin-33 trailers are designed specifically to support this rapidly expanding [system].”

From a technology point of view, Knipling says adding length might aid on-road stability, too. “T-33s [are] more stable and less likely to roll over or jack-knife,” he says, referring to computer simulations using engineering data from the vehicles such as axle weights, axle and hitch locations, suspension characteristics, tyres and payload, as well as research from Canada and Sweden.

He concludes that shifting from twin 28-foot trailers to twin-33s would allow transport businesses to meet the changing nature of retailing while making on-road transportation safer and more sustainable, pointing out that while a 33-foot trailer set-up would be 13.5 per cent longer overall, its cargo capacity would grow by 18.6 per cent – equating to about two pallets per trailer.

As such, a shift would result in better fuel efficiency and lower costs for consumers, he adds. “[It] would save 255.2 million gallons (ca. 966 million litres, ed.) of fuel, reduce carbon and nitrous oxide emissions by nearly three million tonnes and a billion grams respectively – all while reducing shipping costs by $2.6 billion (ca. €2.4 billion, ed.). These emissions reductions would be equivalent to taking 551,000 cars off the roadways.”

According to Knipling, changing to a 10m design would not require a redesign of the 8.5m one already in widespread use in the LTL market – an important consideration to guarantee a swift uptake of the HPFV design. “The 10-feet addition (five feet per trailer, ed.) to overall vehicle length does not change the maximum total vehicle weight of 80,000 lbs or existing axle or bridge formula weight limits. Weighing and inspecting a T-33 is essentially the same [too].”

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