Walmart's supercube performs as advertised on the GHG front. But NOx and PM? Not so much.
TORONTO, Ont. — A new tractor-trailer configuration developed by Walmart, which increases the cubic capacity of the trailer by 30%, requiring fewer truck trips to deliver the same amount of product, could in fact be much worse for the environment than modern conventional tractors pulling 53-ft. trailers.
Walmart unveiled its ‘supercube’ trailer Nov. 6, amid claims the environment would benefit from fewer truck trips. The 60.5-ft. trailer features a lowered floor with a 126-inch interior clearance. It is pulled by a cabover tractor with a dromedary box mounted to the back of the cab, adding another 521 cu.-ft. of carrying capacity and improving overall cargo volume by 30%.
The configuration doesn’t exceed existing length or weight restrictions, but has the potential to reduce truck trips by 30%, Walmart claimed. Painted sky blue with fluffy white clouds, the trailer reads: “Delivering more products using fewer trucks.”
What Trucknews.com has learned, however, is that the trailer is pulled by a Freightliner Argosy cabover glider kit with a refurbished EPA02 generation engine. A glider kit consists of a new chassis, complete with driveline and electrical system, that’s delivered without an engine and transmission. An older generation EPA02 engine has been installed into the tractor, which falls well short of current emissions standards for heavy-duty diesel engines.
The US Environmental Protection Agency (EPA) passed stringent emissions standards in 2007 and again in 2010, which dramatically reduce the allowable output of the smog-forming pollutants particulate matter (PM) and oxides of nitrogen (NOx).
An EPA02 engine had a regulated output of 2.5 grams NOx and 0.1 grams per brake horsepower hour of particulate matter. The EPA10 limits are 0.2 grams NOx and 0.01 grams of particulate matter.
That means an EPA10 engine is 12.5 times and 10 times cleaner than an EPA02 engine in terms of NOx and PM emissions, respectively.
By installing an EPA02 engine into a new chassis, Walmart has effectively sidestepped the two most recent rounds of emissions standards.
By its own calculations, the fuel economy of the ‘supercube’ tractor-trailer will not differ substantially from current configurations widely used today.
“We don’t anticipate there being any significant difference in fuel consumption,” Andy Ellis, senior vice-president, supply chain and logistics for Walmart Canada, told Trucknews.com at the trailer’s launch.
Improving the cubic capacity of the trailer means the new configuration would be able to eliminate approximately one truck trip for every three deliveries. Granted, that will lead to a corresponding reduction in CO2 output (the EPA07 and EPA10 regulations didn’t address CO2). Every truck trip that’s eliminated, every gallon of fuel that’s not consumed, will benefit the environment from a greenhouse gas/CO2 perspective.
But even with this in mind, could an increase in smog-forming NOx and PM offset any environmental benefits achieved through fewer truck trips and reduced CO2 output? I have put that question to several respected mechanical engineers who work in the trucking industry and together we’ve bandied about dozens of possible scenarios.
For starters, it’s important to note these calculations are an inexact science, at best. It’s impossible to take into account every single variable that will influence emissions output. Still, it’s a worthwhile exercise, as the conclusions I’ve arrived at in every instance fail to support any claim that the Walmart supercube is better for the environment than a conventional configuration consisting of a tractor with EPA10 engine pulling a standard 53-ft. trailer.
Let’s begin with the GHG calculations, which indeed paint a favourable picture for the supercube. For our experiment, we assumed a standard 53-ft. van trailer has a load capacity of 4,000 cu.-ft. and the supercube trailer can contain 5,270 cu.-ft. (actual numbers cited by Walmart are 3,900 cu.-ft. and 5,100 cu.-ft., respectively), and a sample size of 42,000 cu.-ft. of cargo.
A standard tractor-trailer could deliver this cargo making 10 trips, while the supercube could move the same amount of freight in just under eight total loads. We’ll assume a trip length of 250 miles (400 kms), averaging 60 mph (96 km/h), totaling 4.1 driving hours per trip. Over the contracted haul, the old configuration would require 41 total operating hours while the supercube could do the job in 32.8 hours. (We’re going to account for the fact that an EPA10 engine with SCR should get slightly better fuel mileage than an EPA02 version, especially in light of aerodynamic improvements made to today’s top conventional tractors).
Supercube with EPA02 engine: At 6.7 mpg, it would require 597 US gallons of diesel over 4,000 miles of travel, resulting in approximately 13,730 lbs of CO2 over the course of the required trips.
Standard tractor-trailer with EPA10 engine: At 7 mpg, it would consume 715 US gallons of diesel over 5,000 miles of travel, resulting in approximately 16,450 lbs of CO2 generated over the required trips.
The result: the supercube would lessen CO2 emissions to the tune of 2,720 lbs over the course of our scenario, hauling 42,000 cu.-ft. of product. This is all very encouraging. But what of the NOx and PM emissions; smog-forming pollutants that were reduced by law in 2007 and 2010? Using the same scenario as outlined above, the NOx and PM emissions would be as follows:
Supercube with EPA02 engine: 2,603 g NOx + 1,037 g PM per load x 32.8 engine hours = 85,378 g NOx and 34,013 g PM.
Standard tractor-trailer with EPA10 engine: 267 g NOx + 133 g PM per load x 41 engine hours = 10,947 g NOx and 5,453 g PM.
All other things being equal, the simulation indicates the supercube truck-trailer configuration could increase smog-forming pollution by a multiple of approximately seven when delivering the same amount of freight. Put another way, for every 10 truckloads of product delivered via supercube, the amount of smog-forming PM and NOx pollution generated would be equal to about 70 truck trips using a traditional configuration with an EPA10 engine.
This clearly contradicts part of what Walmart set out to achieve with its supercube trailer. It also flies in the face of its environmental objectives, as a member of the US EPA Smartway program. My question is, where was the Ontario Ministry of Environment in all of this? Did they not undertake the same exercise I did to uncover these fairly obvious discrepancies? Did they not take a look under the cab to inspect the engine?
Of course, as previously mentioned, these calculations are an inexact science. The engineering source who helped me run this simulation cautioned that a precise comparison is not possible without a CRAY computer and knowing every single spec’ on both vehicles. I sought a second opinion from a mechanical engineer who said the above numbers look “reasonable.”
A third engineer, who works for a respected research organization, took a different track but reached a similar conclusion.
Because the EPA10 maximum output of NOx and PM are 12.5 and 10 times lower, respectively, than an EPA02 engine, and the supercube can do the same job in 22% fewer hours of drive time, he applied a multiplier of 12.5 and 10 to 78% (to account for fewer trips). The result was that total NOx output would be 9.75 times greater and PM output 7.8 times greater than an EPA10 tractor pulling a standard 53-ft. trailer.
Today, much of the attention is on greenhouse gases and CO2 is the next target on the EPA’s hit list. The supercube receives a passing grade where CO2 is concerned. Still, NOx and PM are harmful for the environment as well, not to mention the health of its citizens, which is why the EPA c
hose to target those pollutants first. We can’t ignore the importance of what’s been achieved over the past five years in reducing those harmful pollutants to the tune of about 90%.
The supercube configuration essentially sidesteps those emissions mandates and in the end, opens it up to scrutiny.
In addition to all this, recent conversations with engineers also uncovered another potential fly in the ointment for Walmart’s supercube. Is it even leal to use a glider kit as a new vehicle in Canada? It’s a gray area, so for help I turned to Don Moore, executive director of the Canadian Transportation Equipment Association (CTEA).
His interpretation of the Environment Canada rules on gliders are that they can only be used to replace a wrecked vehicle (where the engine and transmission are salvageable but the body is not); not to circumvent emissions requirements. In the case of a wreck, the glider would be assigned the same VIN as the vehicle it replaced. A new 2012 model year body must be fitted with an engine of the same vintage, Moore said, noting he was seeking clarification on the matter from Environment Canada.
Some may wonder why Walmart doesn’t solve this issue by simply installing a current generation engine? Unfortunately, it’s not so simple. I spoke with John Kennedy, whose used truck dealership Bay Trucks, provided the Argosy tractor and installed the engine and transmission. He said he sourced the world for a suitable tractor that would be able to pull the 60.5-ft. trailer without exceeding maximum overall length limits and the only option was the Argosy.
The Argosy is built by Freightliner for delivery to certain export markets such as Australia and Asia, but it has been discontinued in North America and has not been engineered to accommodate the latest generation engines that meet the new North American emissions standards.
“It’s absolutely impossible to import a European cabover, we’ve tried,” Kennedy said. “We sourced out a bunch of used Argosies but they were all long in the tooth, there was too much refurbishment required, you’d get into stretching frames, shortening frames and changing axles, etc., and not one of them was a day cab; we would have had to cut the sleeper off. We approached Freightliner and they said they still do build Argosies for the Asia and Australia markets in both left-hand and right-hand drive (configurations). They said ‘We can’t sell you one because it was never engineered for the current batch of engines, but we can sell you a glider’.”
That seemed like an ideal solution, aside from the fact that the Argosy chassis could only house a previous generation engine and not the exhaust aftertreatment devices that were introduced in 2007 and 2010 (a diesel particulate filter and selective catalytic reduction, respectively).
Until an EPA10 engine can be engineered into the spec’, I have to wonder why this experiment should be allowed to continue? Walmart will surely refute my numbers and they’re entitled to do so, but I see no scenario in which they can convince me the supercube benefits the environment when taking into account not just GHG, but also the smog-forming pollutants NOx and PM.
I believe what we have in the supercube is an interesting new configuration, cleverly designed, that accomplishes its objective of carrying more freight but fails to fulfill its other mandate in reducing pollution. The supercube may be great for Walmart, but in my opinion it fails society and the environment.