It is also important that the state understands the cost of the PG grade that it requests. The value of crude oils will probably change, and this may affect the price of certain grades of asphalt. Some grades of asphalt are considered beyond the manufacturing capability of today's refineries. But with some changes, maybe they can be produced. To meet some grades, the binder will have to be modified, in turn increasing the cost.
Reliability is the concept that a higher initial cost can be traded off for a longer pavement life.
Because of these factors, a state or agency must use good engineering judgment in selecting the proper PG grade. In other words, if the difference is higher than 90, the asphalt will have to be modified. There are many things that invalidate this rule. Each refiner will have its own production arrangement for manufacturing asphalts. Higher viscosity asphalts tend to have a broader temperature range than softer asphalts.