Why is road smoothness important?

Road smoothness requirements are written into all Caltrans interstate and state highway projects. Contractors are held to high standards to achieve road smoothness tolerances. When pavements are smooth it reduces emissions, reduces vehicle wear and tear, and roads last longer. State DOT’s and government agencies also hear less complaints about pavements with good ride quality. 

How is it measured

The International Roughness Index (IRI) specification used on Caltrans projects account for driver comfort, which is derived from suspension response when a vehicle is driving over the road at 50 mph. This fixed calculation speed is part of the reason why you do not see IRI smoothness specified for city streets at the same level as highways. A 35 mph road in a city does not need the same smoothness as the interstate. The inertial profiler system makes data collection simple – profile data is collected in both wheelpaths without lane closures and large disruptions to the public.

To identify different types of roughness within a project, most DOTs use a 0.1-mile (528-foot) segment Mean Roughness Index (MRI) and Areas of Localized Roughness (ALR). The MRI results depict the average IRI wheelpath roughness for a project section while the ALR are the rapid changes in profile elevation which feel most uncomfortable to the driver. ALR on new pavements are usually a paver stop or joint, equipment breakdown, variability in paver speed or width and road design features. ALR on older pavement can be cracks, potholes, manholes, etc. 

Each year DOTs collect pavement condition data to monitor their network and determine where the future budgets should be used. You can view the 2019 Caltrans State Pavement Report here or view the UCPRC PaveM pavement condition portal. All the data for the networks of each DOT is sent to the Federal Highway Administration (FHWA).

How does the data affect construction? 

Since Caltrans transitioned to inertial profilers in 2013 there have been changes to how roads are built and tested. More data is collected on highways related to rideability than before, which means data can be tested, retested, and checked by the contractor and the State DOT. Asphalt and concrete contractors now have more to consider when making a paving plan. For concrete and asphalt pavements any change in paver speed, paving depth, width, ground condition, or material can affect road smoothness

New technologies related to machine control are emerging to assist contractors in achieving the smoothest pavements and maximizing incentives. Some of the smoothest concrete pavement in California was recently laid using a 3D machine control system. Although variable depth machine control is not required to meet smoothness on every project, an inertial profiler is a useful tool to determine whether variable depth modeling would benefit the final rideability.

In cases where the contractor does not meet the smoothness requirements of the project, the contractor may take a disincentive and pay the State for the deficiencies, correct the roughness, or remove and replace the material. Usually, the latter is not considered based on the high cost. For Caltrans specifications an incentive or disincentive is only allowed for MRI segments and all ALR must be corrected. The most common corrective action is diamond grinding. A diamond grinder is a large planar machine with a wheelbase between 10 and 22-feet. The diamond grinders use 100-300 diamond tipped circular blades to cut the pavement surface. The result is a removal of bumps or undulations reducing the IRI values.


Why is road smoothness important?

How can we help?

G3 Quality is proud to announce we will be supplying inertial profiler collection services starting June 2022. G3 has been a longtime partner of inertial profiler manufacturer Surface Systems and Instruments (SSI). SSI has supplied G3 with the latest in smoothness test equipment; the CS9100 Zero-Speed Inertial Profiler

Using the Zero-Speed system, G3 will collect accurate inertial profiler data at speeds between 0-100 mph including through stoppages. This benefit of highly accurate low-speed data is proprietary to SSI inertial systems. The G3 profiler will simultaneously collect dual wheel path smoothness profiles, cross-slope, right-of-way images, and GPS position for corrective grind layout. 

G3’s inertial profiler is optimized for data collection conditions in California. We comply with Caltrans Test Method 387, FAA airport smoothness, and most other IRI or PRI specifications. The Zero-Speed upgrade is ideal for urban streets and city or county roads. Our operators are prepared to assist with any project phase and create corrective grind plans to elevate efficiency. 

G3 Quality, Inc. is here to provide any further information you may need regarding our inertial profiler collection service. 

We are an elite team of engineers and professionals who provide world-class quality management, pavement engineering, materials design, construction inspection, and testing on infrastructure projects throughout California and the western United States. To learn more about how G3 Quality can contribute knowledge, expertise, consulting, and professional services to your project, contact us.