Even though asphalt would appear to be the best surface, experience has proven concrete to be a better surface and asphalt not to be cost effective over the long term.
Concrete lasts longer, will not break up in the turns, is light-colored, and it does not heat up in the sun as much as asphalt does. The extra heat and rough surface of asphalt can wear out a set of tires in 2 weeks during the peak of the season. In addition, the safety rail shoe tends to sink into the asphalt and it becomes impossible to maintain a consistent rail height. The concrete track should be finished as smoothly as possible. Keep in mind it is easy to acid etch a smooth surface to make it rougher, but it is very hard to make it smoother.