Vehicles of ADOT: Profilometer

ADOT’s job doesn’t end once a road is built.

Continued maintenance is necessary to keep our highways safe and operational for as long as possible. But with more than 6,000 miles of interstate and state highways in Arizona, prioritizing that work takes some effort.

One of the measurements used by ADOT to determine when a stretch of pavement needs rehabilitation is known as the International Roughness Index (IRI) – it’s a scale that measures a road’s smoothness.

You drive how many miles each year?
ADOT’s Pavement Management section gets the data necessary to calculate the IRI by driving all over the state in a vehicle equipped with a profilometer, an instrument that’s connected to an onboard computer system. The profilometer is a complex little device that utilizes laser sensors and an accelerometer to provide accurate results.

Two ADOT employees drive the vehicle roughly 15,000 miles each year to get the data needed!

Two people are necessary to operate the profiler vehicle because one drives (of course!) while the other works the onboard computer to note mileposts and other roadway “events” that would affect readings – think railroad tracks, bridge joints and road debris.

Besides being used by ADOT for project prioritization, the data collected is also sent to the Federal Highway Administration for its annual report on the health of each state’s highway system.

Additionally, ADOT’s profilometer gets called upon to drive project sites before and after a pavement rehabilitation project is completed. That helps ADOT know whether a contractor did a great job, or if some fixes are in order.

Why smoothness matters
ADOT has a limited amount of funding to build and maintain the state's highway system...and every dollar counts.

Maintaining a road is often less costly that reconstructing it altogether, but pavement designers and engineers can't just guess which projects to take on next. The profilometer gives vital data that, along with other factors, helps guide their decisions to make the most of a maintenance budget.

One more thing…
We’ve mentioned that data collected by the profilometer helps ADOT determine when to schedule projects. The projects we’re referring to can range from simple pavement preservation projects to more extensive pavement rehabilitation.

Those preservation techniques include surface treatments such as crack sealing (that’s where a sealant is used to fill cracks in the road) and slurry seal coats, which consist of sand, cement, water and emulsified asphalt. The slurry seal is spread in a thin layer over the pavement to help fill cracks and minor depressions in older asphalt concrete pavement. The more extensive rehabilitation projects require crews to mill and replace existing asphalt pavement.

For more information on how ADOT keeps its roads smooth, check out this blog post and video from 2011 that focus on a profilograph. That’s an instrument similar to a profilometer, but it is used to measure the smoothness of concrete instead of asphalt. If you want to see how ADOT measured the road’s roughness back in 1968, please revisit this recent post.