What is a smooth pavement?  To the traveling public, it is a pavement they can’t ‘feel’ as they travel down the road.  In the minds of the traveling public, studies have shown that the smoothness of a roadway is a factor in whether they believe that roadway is good or not. 

In Wisconsin, the smoothness of a roadway is measured using the International Roughness Index (IRI). In the IRI system, the measured value is in terms of millimeters per meter (mm / m)--so a higher value is a rougher ride.  The smoothness of a pavement is a characteristic that everyone can relate to. Roadways built using HMA are smoother than concrete roads. In fact, historical WisDOT data shows that new concrete construction IRI averages nearly 1.6 while new HMA construction IRI averages around 0.8. That makes HMA essentially twice as smooth (see chart below).

So why are smooth roads so important?  A smooth pavement will not ‘beat up’ your vehicle like a rough pavement will, it is safer for the traveling public, can increase the fuel efficiency of vehicles and reduce vehicle maintenance costs.  Finally, according to the Federal Highway Administration, smoother pavements last longer than rougher pavements, something the tax paying public should expect out of their investments in our infrastructure.