- Roads rumble when trucks roll over them because of a slight deflection caused by the weight. Eliminating that dip with stiffer pavement could improve fleets' mileage efficiency, according to a June paper from Massachusetts Institute of Technology (MIT). Stiffer pavement would cut down the amount of deflection, reducing wear on the road and decreasing the slightly uphill motion the vehicle has to make to rise out of its own depression in the road, the researchers said.
- The MIT researchers found if 10% of road surfaces had stiffer pavement, a total of 440 megatons of carbon dioxide-equivalent emissions would be avoided over 50 years, which is about 0.5% of total transportation-related emissions for this period, according to MIT News.
- There are several ways to make roadways stiffer, the researchers said. "One way is to add a very small amount of synthetic fibers or carbon nanotubes to the mix when laying asphalt," they wrote. "Just a tenth of a percent of the inexpensive material could dramatically improve its stiffness ... Another way of increasing rigidity is simply to adjust the grading of the different sizes of aggregate used in the mix, to allow for a denser overall mix with more rock and less binder."
Getting better fuel efficiency is not just a matter of fleet savings. The less diesel used, the fewer carbon emissions are put into the air. So fleets and researchers are looking at a number of ways to improve fuel efficiency — from aerodynamic tire coverings to road improvements.
The MIT report said smoothly paved interstates alone do not save as much fuel as they could. That's because heavy-duty trucks move over the roads in a different manner than lighter cars.
"When we as individuals walk on pavements, they seem like perfectly rigid things. They're not responding to us,” Randolph Kirchain, one of the report authors, told MIT News. "But for trucks, that is not the case. There is enough of a deflection in that surface that some amount of energy is expended to overcome the little divot that you create as you drive along."
Kirchain compared it to a person walking on a hard surface, as opposed to walking on sand. Walking on sand is harder because it is not solid, and a person tends to sink in before his or her next step.
The researchers noted there could be new costs to asphalt makers. Changing the asphalt mix could mean problems in the field, or have effects on equipment.
The proposal comes as President Donald Trump and Congress weigh an infrastructure bill. Trump has long wanted a bill to fix roads, bridges and ports. In late March, after he signed coronavirus relief in the form of the CARES Act, he tweeted that a new phase of coronavirus relief could be a stimulus in the form of a $2 trillion package that would conceivably cover many of his infrastructure goals, which include fixing, improving or adding to America's roads, bridges, tunnels, ports and airports.
Efforts to negotiate such a bill fell apart in April 2019, when Trump walked out of a White House meeting with House Speaker Nancy Pelosi. But the trucking industry, especially the American Trucking Associations (ATA), has continued to push for a bill that will fund and fix highways, bridges and tunnels.