Trucks at Work
Weighty matters in Maine

Weighty matters in Maine

This research quantifies how the mutual goals of resource conservation and emission reductions could be advanced by allowing Maine to apply state weight laws to its Interstate highways.” –Mike Card, president, Combined Transport, Inc.

I’m sure the howling is only beginning over the American Transportation Research Institute’s (ATRI) recent analysis touting the benefits of expanding the federal gross vehicle weight (GVW) exemption, based on the allowance for higher truck payloads in the state of Maine.


No doubt this is a far more complex issue than merely boosting allowable gross tonnage per tractor-trailer to 100,000 pounds versus the federal limit of 80,000 pounds on interstate highways. Drivers worry about hauling more freight for the same or less pay; state and federal highway officials are concerned about the impact higher tonnage per combination vehicle may have on roadways and bridges. So-called safety groups, of course, will be outraged at the thought of heavier vehicles operating next to everyday motorists.

Yet for all those issues and the glaring fact that ATRI is the research arm of the American Trucking Associations (ATA) – thus making it not exactly an impartial source – the data gleaned from this study is pretty compelling and is definitely worth mulling over as we try to figure out ways to make our freight transportation networks more efficient and environmentally friendly at the same time.

Mike Tunnell, ATRI’s director of environmental research and the principle investigator for this analysis of Maine’s pilot test of higher truck weights, took two 100,000 pound, six axle tractor-trailers (the trailer getting a third axle in order to handle the higher tonnage), both equipped with a 485-hp Cummins engine, and ran them through two detailed simulations: one truck taking state roads, the current route allowed in Maine for trucks in excess of 80,000 pounds, with the other taking the highway, in this case I-95.

The results are pretty interesting:

• Though longer, the truck using the I-95 highway route actually completed the journey in less time – anywhere from 26 to 33 minutes faster. This is due to the overall speeds of the vehicle, with the one on the highway averaging 60 to 62 mph, with the one on the state road going 38 to 42 mph.


• Less fuel was consumed as well by using the highway, anywhere from one to two gallons. In an interesting side note, just stopping at all the traffic signals on the state roads alone was responsible for consuming an extra gallon per trip.

• In terms of overall fuel efficiency, though the I-95 route was longer by about five miles in either direction, the 100,000 pound rig on the state roads posted 14% to 21% better fuel economy than its opposite on the state roads.

• Carbon dioxide (CO2) emissions – the most recent boogeyman in the climate debate – decreased anywhere from 6% to 11% with the heavier truck taking the longer, higher-speed highway route, compared to the local state roads. Again, stopping at traffic signals came with penalties, in this case boosting CO2 emissions by 6% alone.

• Particulate matter (PM) and oxides of nitrogen (NOx) and non-methane hydrocarbons (NMHC) emissions declined 3% to 8% by taking the longer highway route as opposed to navigating the shorter but slower stop-and-go state road route.

Extrapolating these findings over a week’s worth of heavy truck operations in Maine also resulted in some pretty significant efficiency improvements and environmental benefits. By putting 100,000 pound trucks on a longer highway route, total fuel savings could range from 338 to 675 gallons of fuel per week; CO2 emissions would decline by 3.4 to 6.8 metric tons per week, along with 33.8 to 93.8 fewer grams of PM and 8.3 to 24.8 fewer pounds of NOx and NMHC.


So, is allowing higher truck weights of 100,000 pounds on highways – trucks equipped with six axles to reduce the impact of that extra tonnage on roads and bridges, while adding braking power – the “silver bullet” we’ve all been waiting for in terms of how to further reduce fuel consumption and air pollution from heavy trucks?

In a word … NO.

Allowing higher truck weights is but one part of an effort to rethink and retool how we move freight in the U.S. Certainly, allowing tractor-trailers to carry more payload would boost productivity and require fewer trucks on the highway – a way, perhaps, to offset any reductions in drive time as the Federal Motor Carrier Safety Administration (FMCSA) embarks on a two-year effort to re-analyze hours of service (HOS) regulations.

Yet concerns over hauling more for less pay and how heavier vehicle weights affect highway safety are only two of a plethora of issues that arise when talk of boosting federal GVW limits begins in earnest – and they must be satisfactorily addressed, or the effort to raise tractor-trailer tonnage limits won’t go any farther.