Inertial Road Profilers FAQ

Profilers are used to monitor the roughness of the newly constructed roads. The sooner a contractor can perform smoothness measurements on a pavement after it is constructed, the more quickly problems with the construction methods can be discovered. DOT agencies often have pay incentives that are based on the smoothness results collected with a profiler, so understanding how to construct smooth roads is important when considering how to bid a project.

IRI – International Ride Index – is a simulation of the suspension of one wheel in a car that adds up over a given distance, typically 528 feet or 100 meters. The units are usually inches per mile or millimeters per kilometer.

In most cases the DOT is looking for segment IRI calculations, which is what their incentive pay is based on. In some cases the DOT might require localized roughness calculations to also be calculated. When doing localized roughness calculations the same IRI simulation is used, but on a much shorter interval. Typically a 25 foot interval is used so that areas of high localized roughness can be identified and possible corrective measures can be applied.

The reporting interval is usually 528 feet or 100 meters, or for localized roughness calculations 25 feet.

Profilers are sometimes called “Vehicle Mounted Profilographs,” but they use very different technologies to measure roadway profile. Rather than the physical beam with a pivot in the center that Profilographs use, Profilers take advantage of Laser and Accelerometer technology to read the changing height of the roadway. The Laser and Accelerometer work in tandem to cancel out the vehicle’s suspension travel. This results in a profile that is just the surface of the road.

International Ride Index, the main calculation that Profilers do, actually measures the roadway better than Profilographs. This is because Profilographs, being a physical beam, have very odd responses to different feature lengths. Take a look at this plot of a Profilograph’s response:

(source: FHWA Report FHWA-HRT-05-068, October 2005)

Notice in the above plot how the response is much lower than we would want at about 13 feet, and much greater than we want above about 25 feet. This means that there will be 13 foot features that can be missed, and 25 foot features that will be greatly exaggerated. Now compare that to the plot of the International Ride Index response:

(source: FHWA Report FHWA-HRT-05-068, October 2005)

This plot is in meters, but when converted to feet, the response is from approximately 6.5 feet to 65 feet and, while still not perfectly flat, is much closer to flat than the profilograph’s response.

Of course, if a Profilograph response is required, our Ames Profiler software does have a Profilograph simulation analysis option which models the odd response characteristics shown above.

Unless there is a specification that requires the use of a profilograph, we recommend using a profiler in all cases. It is more efficient, more accurate, and safer.

A High Speed Profiler is well suited to surveying preexisting roadways covering a large area. Any time profile data needs to be collected at high speeds or in dangerous traffic conditions, a high speed profiler is preferable and safer. With a high speed profiler system, there is also no need for a trailer for transportation like there is with a lightweight profiler, saving fuel costs as well as space. The frame can be unbolted and loaded into the pickup bed or back of the van for safe transportation.

On the other hand, a Lightweight Profiler is needed any time it would be beneficial to profile a roadway earlier than it will support a full-size vehicle. A Lightweight Profiler exerts about 8 Pounds Per Square Inch of pressure on the ground, approximately the same as a human. A full size car or truck exerts 30 PSI or more. On a concrete pavement section, that means it would be possible to profile the section the day after it is laid instead of waiting a week or more.

We offer two types of sensors, Line and Single Point Laser Sensors.

Line Laser sensors, like our Gocator sensors, excel on concrete surfaces with longitudinal tining or any texture that might falsely affect the profile and smoothness numbers. They do this by measuring a number of points along the line and doing “bridging” between them. This way, the laser closely simulates the contact patch of a tire.

Single Point Laser sensors, like our AccuTexture 100 AR550 sensors, excel on asphalt and smoother surfaces. Like the name implies, these sensors only measure a single point. This allows us to offer an option to add texture capability to our single point lasers, measuring both profile and texture at the same time.

Which sensor is best depends on what surfaces you intend to measure and whether collecting texture data is important. Both types of sensors can be used on our Portable High Speed Profiler system. In fact, the sensors are so easily changed that it is possible to use both types of sensors, swapping them out depending on the surface!

Our Lightweight Profilers can also be outfitted with either line laser sensors or single point sensors, but the vast majority of lightweight profilers we sell are outfitted with line laser sensors.

Our Lightweight Profilers are based on John Deere Traditional Series (TS) Gators.

Any vehicle with a front or rear mounted 2″ trailer hitch receiver can be outfitted with our Portable High Speed Profiler system. A front mounted hitch is preferrable because the machine stays cleaner than a rear mounted system, especially in wet weather. Because having clean sensor lenses is very important to profiler performance, we recommend a front-mounted system.

No, our lightweight profilers do not need generators! Ours are powered directly off the Gator. No more need to fill up the generator and pull the starting cord!