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The backbone of America's economy is its vast roadway system.
Our roads connect people and goods
from one end of the country to the other
and asphalt is important in maintaining that connectivity.
Properly designed and constructed asphalt roads have an important quality
that travelers appreciate - a smooth and quiet ride.
[asphalt paver]
Smoother roads also mean lower fuel costs, less vehicle wear and tear,
and lower emissions.
Engineers use the international roughness index, or IRI,
to measure a pavement's smoothness.
A study in the late 90's measured the effects
of IRI values on fuel economy.
They found a 4.5% improvement in fuel efficiency
and decreased vehicle maintenance costs
after a 10% reduction in IRI.
This represents significant potential savings for truck fleet operators.
[truck passing]
Just as smoother roads mean less wear and tear for vehicles,
they also mean less dynamic loading on the road itself
which can improve pavement life.
Debbie Schwerman: "A smooth pavement will tend to stay smoother longer over time
and a smoother pavement will also require less maintenance over time
and the further you can delay those maintenance costs the better."
Agencies rely on IRI which measures deviation in longitudinal road profiles
to quantify the road condition and help determine when a road
needs maintenance or rehabilitation.
Randy West: "Smoothness is one of the key parameters that states
use to decide you know when a pavement needs rehabilitation
use an IRI, okay? So there's different thresholds that different states will use for
evaluating pavement condition - rutting, cracking, and smoothness."
Agencies can expect different pavement service lives depending upon the initial IRI to which
a pavement is designed and built.
Bill Vavrik: "Well if I design it at a hundred,
or I design it at sixty or design it at forty,
the number of years to get to
a hundred and seventy is quite different, right?
So design, from a structural perspective, the inputs we use in design drive that
lifespan of the pavement. So building smooth roads is really good, you know,
designing smooth roads gives us a longer pavement life."
How can the asphalt industry achieve greater smoothness?
It starts with good workmanship and efficient construction operations.
Andy Mergenmeier: "To pave a road smoothly, the paver has to be fed correctly.
That means the paver hopper needs to be kept full so the paver can move down the
road consistently and smoothly. If a contractor is able to do that, they have
a better chance of achieving the required ride specification."
William Pine "The pavement that we place with the pavers is as smooth as it's going to be.
We don't roll smoothness into the mix when we compact it.
We're trying to not roll roughness into it by the way we compact that mix
and part of it has to do with lift thickness and mix type
that we choose to use or specifications drive us towards."
When agencies apply smoothness specifications, they can use
incentives and disincentives to achieve optimal results on paving projects,
which can have long-term benefits in terms of pavement life and ride quality.
Chris Winiecki: "I think smoothness specifications are changing because of the fact that you
just have a higher expectation from the taxpayer. And as contractors are getting
more and more savvy and capable of getting really good smoothness numbers,
the expectation is to continue to raise the bar on the specification."
"Within the past 15 years, many agencies have incorporated ride specifications
that include financial incentives in their contracts. In general, contractors
working under those types of provisions learn very quickly what modifications
they need to make in their operations to achieve that incentive, and to provide
the required ride quality. On future contracts, contractors can incorporate
what they learned on those contracts to enhance their bids to give them a better
chance to win the next contract that includes those type of
financial incentive ride quality provisions."
The smoother a pavement is built, the smoother it will stay over time,
and the longer it will serve the traveling taxpayer.
Richard Willis: "So people have been doing research for the last 40 years on
different pavement properties and how they impact things like
rolling resistance and sustainability. Everyone always finds that smoothness is
the most important thing. It's not just going to make the ride comfortable,
but it's going to save the general public money and reduce the
environmental impact from the industry."
For more information about asphalt best practices and emerging technologies,
visit the Federal Highway Administration's website.
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