What are the causes of longitudinal cracks and transverse cracks in bituminous pavement?

Longitudinal cracks in bituminous pavement are usually caused by fatigue failure under repeated traffic loading. In thin pavements, cracking starts at the bottom of the bituminous layer where the tensile stress is the highest and then it spreads to the surface as one or more longitudinal cracks. In thick pavements, the cracks usually commence from the top because of high localized tensile stresses from tire-pavement interaction. After repeated loading, the longitudinal cracks develop into a pattern similar to the back of an alligator.

Transverse cracks are usually formed as a result of thermal movement. It may occur because of shrinkage of the bituminous surface due to low temperatures or asphalt binder hardening.

This question is taken from book named – A Self Learning Manual – Mastering Different Fields of Civil Engineering Works (VC-Q-A-Method) by Vincent T. H. CHU.