Wednesday, March 19, 2008

Inertial Profiler versus the California Profilograph

Providing motorists in Ontario with smooth driving surfaces and quality roads are among the top priorities for the Ministry of Transportation (MTO). New pavements with smooth riding surfaces result in lower vehicle maintenance costs and longer pavement life. Since MTO introduced smoothness requirements on new construction projects in 1997, the riding comfort of Ontario highways has improved by some 25 percent.
Currently, the smoothness of newly constructed roads is being measured using a 7.6 m long wheeled truss called a California Profilograph. California profilographs produce measurements of "Profile Index" or PI (for every 100 m pavement section) and bumps or "scallops" for individual features crossing the pavement surface such as joints.

Although the existing system has worked well, California profilographs can only operate at walking speeds and measure one wheel path at a time, which exposes the operator to long periods of time in the construction zone. As a result, the construction industry and MTO are working towards replacing California profilographs with more efficient and safer devices for measuring our new construction contracts.

MTO monitors the roughness of our highway network on a yearly basis using a completely different kind of measurement called International Roughness Index (IRI). These measurements are taken using devices such as MTO's Automated Road Analyzer (ARAN). This means that two different kinds of measurements are being taken on the same pavements. If MTO replaces PI with IRI for our new asphalt construction then, from the time a pavement is constructed until it is rehabilitated, it will be measured using the same kind of index.
All of this has lead MTO to investigate state-of-the-art inertial profilers which can be used to accurately measure IRI on our newly constructed pavements. Inertial profilers are generally classified into two different types – i.e. "lightweight profilers" and "high speed profilers". Lightweight profilers consist of golf cart-like vehicles which operate at speeds of 20 to 40 km/hr and high-speed profilers which can travel at regular traffic speed. Although the ARAN and similar devices can be considered high-speed profilers, such devices are also equipped to measure many other kinds of pavement features causing them to be overkill for simply doing contract smoothness acceptance work. In any case, all inertial profilers are equipped with at least one laser to measure the distance from the vehicle to the road surface and one accelerometer to counteract the bouncing effects that the vehicles experience as they move down the road.
The main benefit of inertial profilers is they can measure both wheel paths, simultaneously (i.e. if two sets of sensors and accelerometers are used) and can report both PI and IRI. Also, since inertial profilers take measurements much faster than the California Prolifographs, they spend less overall time on the road, and are inherently, much safer to operate.

During the fall of 2003, the Bituminous Section at MTO conducted a research project consisting of smoothness measurements on both asphalt and concrete pavements at 8 different locations in eastern Ontario. The project was carried out, in order to compare measurements taken by lightweight profilers, California profilographs and MTO's ARAN. The main objective was to determine how well a lightweight profiler is able to emulate the current PI-based measurements which are taken by California Profilographs, and to determine new IRI-based acceptance criteria which could be used to replace the existing PI-based ones.
Based on the results of this study and more recent work using high-speed profilers, it appears that many of these devices can be used to replace California Profilographs for the acceptance of new asphalt pavement construction in Ontario. In addition, the excellent correlation of IRI found between the lightweight profilers and the ARAN suggests that IRI measurements taken by inertial profilers on newly constructed pavements can be used as the benchmark for the long term monitoring of these roads as they become part of MTO's annual network level roughness measurements.

MTO continues its investigation of state-of-the-art inertial profilers for smoothness acceptance on Ministry contracts. This year, MTO intends to compare side-by-side IRI measurements taken by lightweight and/or high speed profilers with PI measurements taken by California Profilographs on one or more actual contracts. The results of this work will further validate the IRI-based acceptance limits that were determined in the previous study, but in a more realistic contract environment. The results of this work will further validate the IRI-based acceptance limits that were determined in the previous study, but in a more realistic contract environment

MTO and the Ontario Hot Mix Producers Association continue to work together towards the implementation of inertial profilers for smoothness acceptance on MTO's new asphalt construction contracts.

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