Roughness or Smoothness ?
Pavement roughness is generally defined as an expression of irregularities in the pavement surface that adversely affect the ride quality of a vehicle (and thus the user). Roughness is an important pavement characteristic because it affects not only ride quality but also vehicle delay costs, fuel consumption and maintenance costs.

Roughness - “as irregularities of the pavement surface that contributes to an undesirable or uncomfortable ride”
Factors influencing roughness:
-amplitude and frequency of distortions
-vehicle suspension & speed
-used to describe the state of a pavement in service

Smoothness - lack of roughness, used to describe initial state of a pavement.

Today, roughness is typically quantified using some form of either present serviceability rating (PSR), international roughness index (IRI) or other index with IRI being most prevalent.

Surface irregularities:
Concept of wavelength:
< 0.1 m surface texture
~ 0.1 to 0.7 m mega-texture
~ 0.7 to 45 m roughness

Roughness:
0.7 to 2.8 m short
2.8 to 11.3 m medium
11 to 45 m long

Surface Irregularities effects:
Ride:
-less comfort
-motion up/down and vibration
-security
-lost of pavement-tire contact
-increase operating cost
-fuel consumption and increase vehicle wear

Dynamic loading:
hammering effect of heavy axles on pavement structure

Striving for high initial smoothness:
-longer serviceability
(reduction of progression and severity of roughness)
-reduce life-cycle cost
-reduce maintenance cost

Smoothness Indices:
•Roughness/smoothness is characterized by a summary index applies over a length of road
•Measuring the longitudinal profile and applying a mathematical analysis to reduce the profile to a roughness statistic
•Two main indices used
-Profile Index
profilograph
-International Roughness Index (IRI)
inertial profiling devices

“International Roughness Index”(IRI)
-based on non-contact profiling devices
-1.0 km lot with sublotsof 100 m
-smoothness calculated by applying a algorithm to a profile to determine a roughness number

Q: How is it Possible to increase the Smoothness?
A: With Moba Big Sonic Ski - Grade Control Systems

•Long wavelength (11 to 45 m )
With string line

Positioning system, with laser plan and robotic total station

•Medium wavelength (2.8 to 11 m)
mechanical grade control systems with sonic sensors

•Short wavelength (0.7 to 2.8 m)
paver “fixed screws”

Factors Influencing Smoothness
•Best paving practices
-selection of equipment (verification of paving equipment condition; setting up of paving equipment; grade control systems)
-longitudinal
-transversal

•Differential compaction

•Paving material
-adjusted thickness (Nominal Maximum Aggregate Size (NMAS))
-workability (coarse graded mix; fine graded mix; binder content; temperature and temperature segregation)

•Smoothness indices

“Bonuses for good initial pavement smoothness”
“Penalties for not so good initial pavement smoothness”