KPIs or Key performance indicators are used widely within any business operation these days. The rationale behind is “what is getting measured, is getting done”.

What factors determine an exceptional quality road and how can you measure it?

1. Smoothness: Building a smooth road can be accomplished by a good grade control system as it is available widely in the market. Expanding to an averaging beam with three grade sensors or multi-sonic sensors will highly improve a flat surface. Besides building a better long-lasting road, it can also greatly support fuel savings for up to 4% as a study from the University of Auburn found out. Smoothness can, of course, only be achieved with solid paving practices which starts with the focus on each layer put down and other common practices. Check out our Best Practice Presentation for more details on how to increase smoothness. Smoothness can be measured by IRI scores . These scores vary state by state in the US. IRI scores in Pennsylvania range for example in between 35 and 55 to be eligible for a bonus; other states might have totally different incentive bandwidths depending on each state’s criteria.
2. Thermal Imaging: The main problem causing thermal segregation is that the temperature of the laid asphalt is not homogeneous. This is caused by the cool-down process of material during transport. The result is insufficient density and an increase in air voids which leads to premature failure of the street. As a rule of thumb, 1% in increased air voids decreases the lifespan of a street by about 10%. Monitoring the asphalt temperature during that process and applying corrective action early can highly improve quality and life of a road. Using a MPV (Material Transfer Vehicle) can also greatly lower the risk of thermal segregation. Thermal segregation can be measured by temperature differentials which is the highest and lowest temperature measured within a set section. As an example, a temperature differential of 25 degree Fahrenheit leads to an increase of 1 to 2% in air voids and a 10% less life-time of a road. Asphalt temperature can be measured for example with infrared cameras and infrared sensor bars (or scanner).
3. Compacting: Rolling the right amount of passes and compacting in the optimum temperature range (210 to 350F or 100 to 180 degree C) will expand the lifespan of a road. A good starting point could be a basic system by setting and rolling a fixed amount of passes. More advanced systems have acceleration and temperature sensors and use RTK for more accurately defining the GPS locations. The widely used term for such a system is called an Intelligent Compaction System (IC). Several pilot projects are underway measuring and determining what compaction values ensuring a quality road. Accelerometers measure the stiffness of the underground. Experts agree that there is a correlation between stiffness and density found in soil compaction. However, a correlation between stiffness and density in HMA is not proven and still up for discussion.

Some would consider these factors common paving practices and don’t see a need to define a quality road with key performance indicators. Others would agree to the statement above “what is getting measured is getting done”.

What is your opinion?