According to the Scrap Tire Management Council (STMC), over the past 10 years, the recycled content in new tires has increased from 0.5 percent to 5 percent by weight. In some cases, incorporating either recycled content or factory excess of up to 10 to 15 percent in new tires was reported as technically feasible, without adversely affecting the performance characteristics of tires. Previously quoted values of 15 to 25 percent recycled content being feasible without affecting performance could not be verified at the time this report was written. Furthermore, the data indicated that once recycled content reached certain levels, the lifespan of a new tire could be adversely affected. Moreover, in a study conducted by Continental Tire North America (CTNA) for the North Carolina Division of Environment and Natural Resources (NCDENR), CTNA formulated compounds with up to 13.6 percent recycled content but concluded the tires may not be commercially viable due to reduced tread life and wet traction, as well as higher rolling resistance . Finally, other factors such as economics (for example, transportation costs, energy cost, and low price of virgin rubber), availability of supplies, and crumb rubber quality limited recycled content to about 5 percent or under (by weight).