In 1987, in the US, a committee started searching about how to improve performance and durability of bitumen in asphalt roads. This committee named STRATEGIC HIGHWAY RESEARCH PROGRAM (SHRP).
Due to the lacks and faults of the production method at that time, focus of this research program was to discover the lacks that bitumen may show in real environment while used is asphalt. So in laboratories a situation similar to what in real asphalt in long time exposures, is simulated and bitumen is analyzed this way to discover its performance in real situation. The bitumen that is manufactured using this method of testing is called PG (performance Grade Bitumen).