Road material is a term used to describe the materials used to construct roads. TAR, TARMAC, and MACADAM are three common road materials. TAR is a black, viscous liquid made from coal, wood, or petroleum. TARMAC is a mixture of TAR and aggregate, such as gravel, which is used to create a hard surface for roads. MACADAM is a type of road construction in which layers of crushed stone are compacted together with a binding material, such as TAR.