Pavement roughness testing is performed on approximately 30,000 miles of roadway annually in Pennsylvania. Historically, pavement roughness data was collected for the Interstate system and one half of the other routes every year. That way, data was collected for the entire system every two years. Beginning in 1996, the entire National Highway System (NHS) was tested every year; non-NHS routes followed the same biennial cycle. International Roughness Index (IRI) data is also collected for recently repaved, new or rebuilt roads, this varies from year to year, but in 2007 this was an additional 3000 miles of testing.
Roadway Inventory and Testing Unit (RITU) currently owns three full sized highway speed Mobile Data Recorders model (MDR) 4185-L2, manufactured by International Cybernetics Corporation, of Clearwater, Florida. These devices, called Road Profilers, are vans equipped with an on-board computer that is interfaced to lasers and accelerometers which are mounted along the front bumper. The system hardware consists of an IBM-PC compatible computer System Unit with associated Super VGA monitor, compact keyboard, printer and RS-232C Serial Interface. A Data Measurement Subsystem installed in the System Unit provides interfaces to a transmission mounted distance transducer and a custom designed Event keyboard.
The system accepts a downloaded Roadway Management System (RMS) file containing all roadway information as an input database for test data. Vehicle location and roadway features are displayed on the computer screen in a Straight Line Diagram (SLD) format, and the software accepts operator inputs verifying segment locations, known as “events.” Routes can be tested in increasing or decreasing segment order, and test sections may begin on a segment beginning, ending, or any permanent landmark feature.
There are two laser height sensors and two accelerometers. One height sensor and one accelerometer is located over each wheelpath; they function together to allow road profile and surface height data to be collected independent of the travel speed and vehicle characteristics.
An additional laser height sensor is located between the wheelpaths; this sensor along with the height sensors located at the wheelpaths measure pavement rutting information. The test method and equipment used for pavement roughness data collection are defined in ASTM E 950.
Two persons are needed to perform testing, a driver and an operator. Typically, the operator is a permanent Roadway Programs Technician 2, and the driver is a temporary Roadway Programs Technician 1. Testing is typically performed during the months of March through November, but can vary depending on weather conditions. During the winter months, test results may misleadingly indicate rougher roadways due to the pavement surface characteristics caused by colder pavement temperatures.
Roughness testing is typically performed while traveling at normal highway speed continuously along a route within a county from the beginning of the route to the end. The operator signals the beginning of each segment as the vehicle travels along the route. The laser sensors make measurements at the rate of 32,000 per second, and a profile value is recorded for each traveled distance of six inches. Average IRI values are determined for each tenth mile and for each segment.
The results of pavement roughness testing are IRI values, expressed in terms of slope, typically inches per mile.