Transverse variation of asphalt rate (TVAR) is the seal coat practice of varying the amount of asphalt being applied across the width of the pavement to better match the asphalt needs of the existing pavement. Figure 4-2 shows a pavement where the texture varies across a pavement and is a prime candidate for using the TVAR technique. The reason becomes more obvious in the inset images of the magnified pavement surfaces in the wheel path, on the right, and outside of the wheel paths, on the left. One can readily see that less new asphalt is needed in the wheel paths to hold the new aggregate than is needed between the wheel paths. Between the wheel paths, there is some texture that needs to be filled with asphalt before the remaining asphalt can effectively embed and hold the new aggregate. So when shooting one rate across the pavement width, either there is more asphalt than needed in the wheel paths, with the obvious consequences, or you have at best marginal asphalt being placed between the wheel paths, which increases the chance of losing aggregate.�

TVAR can improve the performance of seal coats, particularly those placed on pavements with flushed wheel paths. Existing wheel path flushing can be reduced and sometimes eliminated, thereby significantly improving skid properties of the roadway while still providing adequate asphalt outside of the wheel paths to hold the new aggregate.�

A common misconception is that TVAR reduces the amount of asphalt being placed on the roadway. TVAR actually increases the total amount of asphalt being used if prior practice has been to design the asphalt rate based only on wheel path conditions.�

Optimal performance requires that the wheel path need for asphalt be met as accurately as possible. Then with TVAR, the asphalt rate outside of the wheel paths is increased. The net result is that more asphalt is usually placed on the roadway than would have otherwise occurred.�