Using computer modeling, Professor Franz-Josef Ulm and PhD student Mehdi Akbarian demonstrated that because of the way energy is dissipated, the maximum deflection of the tire load is behind the path of travel. Imagine a ball rolling across a pillow. Because of the "give" of the pillow, the ball is continuously rolling uphill, even if it's rolling in a straight line. This means more force must be exerted to push the ball forward.
The same goes for tires. Softer road surfaces, like thinly layered asphalt, tend to absorb energy and cause increased fuel consumption.
Previous studies used empirical testing, but external factors made it nearly impossible to get consistent results. The researchers instead took samples of over 5,000 different roads around the United States and developed computer models around them.
In the end, spending the extra money to build stiffer and stronger roads doesn't just save the motorists money, it makes for longer-lasting roads, too. Roads which won't have to be repaired as often.
In the bid to lessen our dependence on foreign oil, a 3% decrease in fuel consumption, as well as the need for less asphalt for road repairs (asphalt sourced from oil) seems like a sure-fire solution that's both green and economical.
Now if only we could get our politicians to accept the possibility of less kickbacks from road repair projects.